Senior Project

i
ADDITION OF FREEZE-DRIED APPLE SKINS AND THE EFFECTS ON PHENOLIC
CONTENT IN HARD CIDER
By
Megan Bocchino
Ashley Long
A Senior Project submitted
In partial fulfillment of the requirements for the degree of
Bachelor of Science in Food Science
Food Science and Nutrition Department
College of Agriculture, Food, and Environmental Sciences
California Polytechnic State University
San Luis Obispo, CA
June 2015

ii
Table of Contents
Abstract……………………………………………………………………………….………..…iii
List of Tables…………………………………………………………………………………..…iv
List of Figures……………………………………………………………………………………..v
Chapter I – Introduction
History…………………………………………………………………………………….1
Processing…………………………………………………………………………………2
Balance of Sugar, Acid and Tannin……………………………………………………….5
Chapter II – Review of Literature
Cider Characteristics from Tannin………………………………………………………..8
Nutrients Derived from Tannin……………………………………………………………8
Phytochemical Properties of Tannin………………………………………………………9
Antimicrobial Effects of Tannin…………………………………………………………10
Changes in Tannin Content………………………………………………………………11
Tannin Additions………………………………………………………………………...15
Tannin Preservation and Freeze-Drying Applications…………………………………...18
Measuring Tannins……………………………………………………………………….19
Chapter III – Materials and Methods……..……………………………………………………...22
Chapter IV – Results……………..………………………………………………………………24
Chapter V – Discussion, Conclusion, and Future Research……………………………………..25
References……………………………………………………………………………………….29

iii
Abstract
Tannins provide body and notable characteristics to hard apple cider; these polyphenols
are much more concentrated in apple skins, which are not included in conventional cider
fermentations. The goal of this experiment was to add variable quantities of dessert apple skins
to post-fermented hard cider to test potential increases in tannin concentration, subsequently
producing a higher quality product. Five 5-gallon carboys of hard cider received varying
concentrations of freeze-dried powdered apple skins, ranging from 1.12 g to 11.2 g. An
additional highly concentrated sample, Carboy 6, consisting of 2.5 gallons of hard cider and 18.0
g of freeze-dried apple skins was evaluated as well. Samples were analyzed for physicochemical
properties at time zero and after 24 hours, 7 days, and 12 days of extraction; total phenolics was
measured using the 280 nm absorbance method. The control, Carboy 1, contained the least mean
total phenolics of 23.913 ± 0.576, while Carboy 6 contained the greatest mean total phenolics of
25.300 ± 0.141. Carboy 1 also contained the least amount of RS, 0.044 ± 0.014, while Carboy 6
contained the most with a significant increase of 0.256 ± 0.006 RS. Despite this overall increase
in RS with the increase in apple skin concentrations, the RS decreased between Carboys 3 and 4
then steadily increased again from Carboys 4 to 6. Based on the current experiment and literary
research, freeze-dried apple skins have shown to contribute sufficient polyphenolic compounds
to hard cider with the goal of enhancing desired cider qualities in addition to the ability to
provide notable amounts of residual sugar.

iv
List of Tables
Table 1 - Apple classification based on acid and tannin………………………………………...12
Table 2 - Comparison of pot-grown 'fed' and 'unfed' Dabinett trees and fruit………………......14
Table 3 - Experimental concentrations of powdered apple skin additions and physicochemical
properties hard cider carboys………………………………………………………………….....24

v
List of Figures
Figure 1 - Structure of linked (-)epi-catechin units……………………………….……………..10

1
Chapter I – Introduction
Hard Cider Background
History
Hard cider, or simply cider, refers to the alcoholic beverage produced from the
fermentation of apple juice. The origins of cider date back centuries to the Celts who presided in
present day European regions and brought cider to north and western territories from the Basque
region. Cider rose in popularity throughout Western Europe before spreading to America during
colonization. In America, cider was the preferred beverage as fermentation helped reduce the
risk of contamination, whereas water could be easily contaminated and polluted. Cider was
considered a family drink due to its perceived health benefits; the alcohol content was low
enough that children could drink the beverage diluted or undiluted. Cider retained its popularity
until the Industrial Revolution during which quality declined as farmers began to move into
cities. Cider production fell sharply in the United States during the Temperance and Prohibition
movements in the 19th and early 20th centuries. Widespread abandonment of cider apple
orchards resulted, some of which were converted into dessert apple orchards instead. This
decline can also partly be attributed to the migration of German immigrants and beer into the
United States, shifting the major preference of alcohol from cider to beer (Janik 2011).
Cider production has only recently begun to rise again in the United States. Retail cider
sales alone have increased as much as 71% in 2014, 89% in 2013, and 90% in 2012 according to
Nielsen Media Research (Cider Journal 2015). While the rate of growth has begun to plateau,
sales have not. Total value sales in 2013 reached US $1.3 billion, largely due to the entrance of
Anheuser-Busch and MillerCoors into the cider arena. US cider and perry, a hard cider made
with pears, are forecasted at a total volume Compounded Annual Growth Rate, CAGR, of 35%

2
to reach 785 million liters by 2018 (Euromonitor 2014; Euromonitor New Product Launches
2015). The present rise in hard cider consumption, particularly by the female population, is
filling the gap left by the decline in beer consumption (State of Craft Beer Industry 2013).
Despite this, there are very few cider apple orchards remaining in the United States.
Many of the trees present have been abandoned for decades and therefore go unnoticed or
unattended. Thus, there is a much greater presence and availability of dessert apples for cider
makers to use. Unfortunately, dessert apple based ciders tend to be unbalanced due to the lower
tannin content of the apples. There is currently no apple tannin available for cider makers to use
as additions to improve body and quality of the final cider product.
Processing
Harvesting
Although cider can be made from any type of apple and of any ripeness level, good
quality cider is made from mature and ripe apples in which all of the starch has been converted to
sugar. Rotten or deformed apples, known as cull, will lead to low quality, short life, and
acetification, while underripe apples may produce indigestible alcohol due to the high starch
levels. These undesirable apples are separated during harvesting while desirable apples are
further processed.
Storage
During the cidermaking process, storage of apples before processing is dependent on the
maturity of the fruit when picked, and thus, how high their sugar content is. If the apples have
reached optimum ripeness by the time they are harvested, the apples may be processed right
away. If the apples need to further mature, they are stored in bulk, avoiding contact with the

3
ground or soil to prevent contamination during storage and subsequent transfer to the mill.
Apples of different varieties are typically stored in separate areas in the event of different
ripening rates.
Milling
The apples are milled, meaning they are ground into a pulp, after they have reached the
proper level of ripeness. There are several types of mills available, ranging from more primitive
to those that use efficient machinery and produce higher yields. Mills generally involve two large
rollers or knives that revolve, cut, and grind the apples. The resulting mash is termed pomace and
is sometimes left to macerate for a few days.
Pressing
The pomace is then transferred to a cider press to separate the juice from the pulp, also
referred to as the cheese. The pomace is pressed, broken up, then pressed again to extract all
juice. The juice may be fermented immediately or may be concentrated, removed of pectin,
pasteurized, and stored for later use.
Keeving
Keeving is an optional process that refers to the clarification of the juice before
fermentation. This clarification lowers the concentration of yeast nutrients and allows for a much
slower fermentation. The result is a hard cider with a higher residual sugar that can later be
naturally carbonated with yeast while ensuring that the cider will not begin to referment.
Keeving is generally practiced when making traditional French ciders (Cidermaking on the Farm
1934).

4
Fermenting
During fermentation, natural yeast present on the apple skins, as well as added yeast,
convert sugar in pressed apple juice into alcohol. The more sugar that is converted, the dryer the
cider will be. The percent alcohol of the final product depends on the amount of sugar initially
present in the juice, with more sugar leading to higher alcohol content. In large scale practices,
SO2 is added to inhibit bacterial growth as well as wild yeast, after which pure yeast cultures are
added; this practice helps to ensure consistent products. Fermentation may be stopped as soon as
the desired alcohol content is reached (Grafton 1996).
At this time, a cider may go through a second optional fermentation called malolactic
fermentation, or sometimes referred to as secondary fermentation or ML. Malic acid, naturally
present in the apples and produced during primary fermentation, is converted to lactic acid and
carbon dioxide through the use of bacteria rather than yeasts; diacetyl may also be a byproduct.
The new lactic acid has a softer, less astringent mouthfeel and has the ability to create complex
sensory characteristics. Complete malolactic fermentation is typically undesirable because it
contributes off-flavors to the cider.
Racking
Racking is simply the transfer of the cider from one container to another and leaving the
sediment and dead yeast, known as lees, behind so as to not contribute unwanted flavors to the
cider. This process typically occurs after the first fermentation; a cider may be racked multiple
times as particulate precipitates out (Homebrew Helper 2014).

5
Filtering
Filtering can be completed in several stages throughout a cider’s life. At home, cider
makers will use fining agents, such as gelatin, to clarify and filter remaining particulate within
the cider. On commercial scales, the cider will pass through mechanical filters, generally
containing diatomaceous earth, to create a more brilliant cider.
Carbonation
Carbonation is either natural or an optional additional step to cider making that improves
flavor, adds tactile and sensory characteristics, and lowers pH.
Bottling
Bottling is usually completed in late winter. Bottles are stored in cool dark places for
several months to prevent temperature degradation or oxidation while simultaneously aging the
cider to develop complex and mature flavors (Harte and Popa 2002).
Balancing Acid, Sugar, and Tannin
Acidity is typically measured by pH, Titratable Acidity (TA), or Volatile Acidity (VA).
pH is the measurement of the concentration of dissociated hydrogen ions in a solution, or how
acidic the solution is, and is measured with a pH meter. pH is often used in the determination of
the SO2 concentration to be added to cider. Good quality cider has an ideal pH between 3.3 and
3.5. Titratable Acidity measures acid in fermented foods and helps indicate flavor profiles of the
cider. TA is often reported as the malic acid content of the cider (Micro Manual 2015).
Volatile Acidity is a negative attribute in cider caused by microorganisms such as
Saccharomyces. In large amounts, VA is indicative of spoiled cider. Acetic acid is the main

6
volatile acid in juice and can be measured through steam distillation along with ethyl acetate,
lactic acid, and succinic acid (VA and Oxidation 2011). VA can be prevented by reducing the
amount of oxygen that comes in contact with the cider and by adding SO2 to inhibit microbial
growth. VA measurements omit CO2 and SO2 in analyses as they are not volatile compounds and
can interfere with the actual VA measurements (UC Davis 2004).
Sugar content is represented as °Brix which refers to the measurement of total soluble
solids in a liquid, calculated as grams of solid per 100 grams of solution. Two methods,
refractometry and hydrometry, are typically used for measuring °Brix in cider. Refractometers
measure the refractive index of the sugar in the solution and report the number as °Brix with no
further calculations required. Hydrometry is the measurement of the specific gravity, the ratio of
the density of the cider to the density of pure water, to determine the sugar content. Higher sugar
contents lead to denser fluids, causing the hydrometer to float higher. As sugar is converted to
alcohol through fermentation, the hydrometer will lose buoyancy due to the lower density of
alcohol than sugar (Harte and Popa 2002).
After a cider has fermented, sweetness is typically measured in residual sugar, RS, or the
amount of sugar in a given volume of cider, generally expressed in grams per liter. Dry ciders
will typically have an RS below 0.5%, off dry ciders will contain residual sugar varying between
1.0-2.0%, semi-dry and semi-sweet ciders vary between 2.0-4.0% residual sugar, while sweet
ciders will contain 4.0% or more RS (The Cider Press 2011).
Polyphenols are an important component to the final quality of cider. Types of
polyphenols found in apples include: phenolic acids, epi-catechin, and dimeric and trimeric
proanthocyanidins (generally termed proanthocyanidins), also known as condensed tannins.
While tannins are concentrated mostly in apple skins, they can be found in the seeds and pulp as

7
well (Guyot 1997). Tannins are found in higher concentrations in bittersweet apples. Low tannin
levels are considered undesirable as the resulting cider will be insipid or bland, lacking in body.

8
Chapter II – Literature Review
Cider Characteristics from Tannin
Phenolic compounds are secondary plant metabolites, meaning they are not required for
the plant to survive. Consumption of these compounds in small amounts is present in daily life,
from fresh fruits, such as apples, and processed foods made from these fruits. Phenolic
compounds are important components of fruit wine in influencing organoleptic characteristics
such as clarity, color, bitterness, astringency, taste, and aroma, which define the overall
mouthfeel of ciders (Ye 2014). In addition, phenolic compounds in apples can prevent oxidation
within hard cider as well as different chronic disorders in humans such as cancer and
cardiovascular disease. Polyphenols present in apples are classified into hydroxycinnamic acids,
dihydrochalcones, flavonols, and anthocyanins (Heikefelt 2011).
Nutrients Derived from Tannin
In a study conducted by the Institute of Food Research (IFR) Norwich, Dr Caroline
Walker of Brewing Research International, Surrey, discovered after analyzing 18 UK ciders that
“cider has the same levels of antioxidant polyphenols and tannins as red wine" and cider
antioxidants were absorbed very quickly, increasing their effect (Apple Nutrition 2005).
Anthocyanins, a type of polyphenol found particularly in apple skins, has an inverse relationship
to coronary heart disease. The concentration of anthocyanins in apple skins relies largely on each
piece of fruits contact to sunlight while it is growing. More exposure of the skin to sunlight and
the corresponding increase in anthocyanins also results in a more red color in the mature apple. If
more fruit is growing on a tree, there will be more competition for sunlight and, thus,

9
anthocyanins. Strong nitrogen fertilization of apple trees also has inhibitory effects on skin
pigmentation. Contrarily, calcium sprays, which are applied to trees to reduce bitter pit and
senescent breakdown, help increase anthocyanins, epicatechins, total flavonoids, chlorogenic and
total phenols (Treutter 2001).
Phytochemical Properties of Tannin
Of the polyphenols found in apples, proanthocyanidins, or just procyanidins, are
considered true tannins as they can tan proteins (i.e. animal skins); thus they contribute to the
browning of apples and apple juice in addition to providing bitterness and astringency (Guyot
1997). (-)epi-catechin units, which were found to be present at a high concentration, 2-3 g/L, in
cider made from bittersweet apples, link together to form oligomeric procyanidins (Fig. 1). This
linking in turn influences the bitterness and astringency of the cider product. Procyanidins with 2
to 4 (-)epi-catechin units results in more bitterness, while 5 to 7 linked (-)epi-catechin units result
in more astringency, which is typically less desirable than bitterness in a cider (Chemistry World
2014). The differences in the size of polyphenol oligomers at maturation relies more on the
variety of apple than on how mature the apples are, variances for a specific harvest year, method
of cultivation, or storage (Renard 2007).

10
Figure 1 - Structure of linked (-)epi-catechin units (Guyot 1997)
Antimicrobial Effects of Tannin
Aside from providing nutrients, plant proanthocyanidins are known as the functional food
factors that possess a variety of physiological activities including antioxidant and antimicrobial
activity (Ashok 2012). One previous study examined the antimicrobial effect of these
compounds from the skin of 2 apple varieties, Royal Gala and Granny Smith, against human
pathogens. The phenolic compounds were extracted with the following solvents: A: acetone,
water, and acetic acid; B: ethyl acetate, methanol, and water; and C: ethanol and water. Total
phenolic, flavonoid, and non-flavonoid contents were analyzed in the extracts. The highest
inhibitory effect of both apple varieties corresponded to extract A, acetone, water, and acetic
acid, which contained a high phenolic content. The Granny Smith extracts with higher phenolic
content presented a superior antimicrobial effect against the selected microorganisms:

11
Escherichia coli, Escherichia coli ATCC 25922, Escherichia coli ATCC 35218, Staphylococcus
aureus ATCC 25923, Staphylococcus aureus ATCC 29213, Pseudomonas aeruginosa ATCC
27853, Enterococcus faecalis ATCC 29212, and Listeria monocytogenes. The results obtained
demonstrate a direct relationship between the phenolic content of the extracts and the
antimicrobial effect (Alberto 2006).
Changes in Tannin Content
The apples chosen to produce hard cider have a dramatic effect on both the flavor and
sensory components of the beverage, as well as the total phenolic content. The amount of
polyphenols varies between different apple varieties as well as by growth conditions, maturity,
and processing within a particular variety.
Tannin Concentration in Apple Skins
Different locations in an apple correspond to different levels of tannins and phenolics.
When comparing apple flesh to the skin, apple skins are much richer in procyanidins, the
phenolic compound mainly responsible for the high antimicrobial effects in apples. After HPLC
evaluation, these tannins have been proven to be more highly polymerized than those within the
flesh. The high levels of polymerization may attribute to a softer astringency and mouthfeel
when apple skins are used as the main source of phenolic compounds for a cider (Guyot 1997).
Apple Varietal
Apples are characterized as bittersweet, bitter-sharp, sweet, or sharp. This classification is
derived from the acid and tannin ratio of the specific apple variety. As indicated in Table 1,
bittersweet varieties contain higher tannin but lower acid, resulting in superb cider quality.

12
Classification Acid (%) Tannin (%)
Sharp > 0.45 < 0.2
Bittersharp > 0.45 > 0.2
Bittersweet < 0.45 > 0.2
Sweet < 0.45 < 0.2
Table 1 - Apple classification based on acid and tannin (Mainstream Cider Making 1995)
In a study evaluating the relationship between tannin concentration and location in
Spartan, McIntosh, Newtown, Royal Gala, Jonagold, Red Delicious, and Golden Delicious
apples, Red Delicious apples had the greatest amount of condensed tannin in the peel and pulp,
whereas Golden Delicious had the least. The peels contained the highest concentrations of
tannins, specifically in the hypodermal cell layer adjacent to the epidermis with a lower
concentration closer to the cortex. The amount in the seed was low and variable (Lees 1995). An
additional study that isolated 5 different tannin types in 20 different apple varieties also showed
that tannin contents range between cultivars as well as the location in the apple; the lowest being
0.9 μg/g wwb in the flesh of Newtown Pippin and the highest being 453 μg/g wwb in Red
Delicious peels. Of the 20 varieties, Harrison, Granny Smith, Rome, Winesap, and Black Twig
apples had the highest concentration of flavon-3-ols, meaning these cultivars are able to provide
desired bitterness and astringency to cider even if processing conditions did not produce enough
tannin extraction from the skins (Thompson 2014).

13
Tannin Content and Apple Maturity
Both cider and dessert apples contain the same types of polyphenols, however
concentrations vary between the two; again due to the different growing conditions, cider apples
tend to have concentrations of all polyphenols in comparison to dessert apples. Flavonols and
anthocyanins are found primarily in the skins while procyanidins, hydroxycinnamic acids,
monomeric flavan-3-ols, and dihydrochalcones are most concentrated in the flesh. Among both
varieties, polyphenol content varies with fruit maturity; the apple’s concentration of apple
condensed tannins (ACT) are found to be at highest concentrations in unripe apples, roughly 10
times higher than in the mature apples. Catechin and hydroxycinnamic acids are also present in
high concentrations at early stages of growth and decline dramatically through maturity. The
largest decline in total phenolic concentration occurs as the fruit matures; however the rate of
decline is not equal among each individual polyphenol compound (Ashok 2012).
Tannin Content and Apple Growth Conditions
Tannins contribute defensive and protective properties within plants. Due to this, the
extent of the composition largely depends on the environment in which they are grown as well as
genetic factors. Similarly, apples grown in harsh weather conditions or with lower levels of
nitrogen will have more tannin. Thus, bittersweet apples will have greater tannin content
compared to sweet apples. (Tannin in Cider Apples 1995). In juice from cider apples, the
content of procyanidins is higher compared to juice from dessert apples, resulting in a greater
bitterness and astringency as well as higher antioxidant characteristics (Heikefelt 2011).

14
Fed (nutrient rich) Unfed (stressed)
Leaf color Deep Green Pale Green
Fruit Color Brown Red
Leaf Nitrogen (%) 2.34 2.00
Leaf Potassium (%) 1.4 1.2
Crop weight (lbs) 65 42
Juice Specific Gravity 1.057 1.057
Juice acidity (% as malic) 0.16 0.15
Juice pH 4.25 4.25
Juice nitrogen (mg per 100 ml) 6.8 3.3
Days of fermentation (inoculated yeast
AWY 350R)
32 70
Tannin (Lowenthal permanganate
titration %)
0.30 0.35
Perceived cider astringency (trained
sensory panel at p = 0.1)
Least Most
Perceived cider bitterness (trained sensory
panel at p = 0.05)
Least Most
Table 2 - Comparison of pot-grown 'fed' and 'unfed' Dabinett trees and fruit (Tannin in
Cider Apples 1995)
Tannin Content and Processing
Tannin and polyphenol content varies dramatically as the fruit is subjected to different
processing conditions. As the fruit is mashed and pressed, the average degree of polymerization
of polyphenols is notably reduced. This may attribute to harsher, more astringent sensory
characteristics (Guyot 2003).

15
The effect of oxygenation and the length of time the pomace is in contact with the air also
can greatly hinder the presence of all phenolic compounds within apple juice; catechins and
procyanidins are most greatly affected, while caffeoylquinic may be slightly preserved (Guyot
2003). Oxidation irreversibly traps procyanidins in solid particulate which is then generally
removed through pressing and clarification; this can significantly alter the concentration of
tannins available in the cider. The rate of oxidation may be inhibited through the addition of
ascorbic acid or metabisulfite or by heating; however, all three of these practices may alter the
sensory characteristics of the cider (Heikefelt 2011).
Tannin Content and Fermentation
During fermentation, the total phenol concentration can show dramatic fluctuations. The
adsorption and desorption ability of yeasts within the cider may alter binding with tannins and
other phenolic compounds. However, post fermentation, tannin content tends to increase slightly
(Ye 2014).
Tannin Content and Heat
Phenolic compounds are also affected when subjected to heat. Tannin concentration
increased at a linear rate of both time and temperature; the astringency and bitterness of products
with tannins subjected to heating proved to increase as well (Watson 2009).
Tannin Additions
There is no set optimal time to add artificial tannin to a cider; the decision ultimately
settles at a cider maker’s personal preference and goal of astringency for the type of cider being

16
made. However, different additions done at different times can affect the level of tannins present
within the cider as well as sensory attributes.
When working with powdered or aqueous solutions of tannin for additions, as well as
fining agents, results are typically seen within 24-48 hours. For this reason, the rate of extraction
is not nearly as critical as the concentration of said addition (Winemaker 2002).
Tannin Additions During Fermentation
One of the earliest tannin addition stages begins with fermentation. These tannins,
typically extracted from grape seeds, can be found in a fine powder and are used extensively in
the wine industry. Use within the cider industry increases particularly as difficulty growing
healthy cider apples continues. Issues arise, however, as grapes and apples have different tannin
structures and are present at varying levels between the two fruits. For this reason, some cider
makers are hesitant to add such grape tannins for fear of interfering with the naturally present
apple tannins (The Science of Cidermaking 1997). The advantage of making tannin additions
early in the cider making process is the increased agitation from carbon dioxide produced during
ethanol production. This agitation permits the tannins to fully integrate with the apple juice and
provide color stability as well as increased middle palate structure (Scott Lab 2010).
Tannin Additions During Aging
The use of oak or oak adjuncts in cider making have seen growing popularity as the drink
continues to evolve. The addition of these adjuncts not only provides sensory attributes but
contributes to the levels of tannins within the cider, prepares the drink for aging, and may protect
against oxidation. As tannins oxidize, they begin to polymerize with other shorter chains; these
polymerized tannins have a less astringent mouthfeel and thus create a higher quality product.

17
Oak tannin additions act as an interferent for the natural tannins present within the cider,
oxidizing, and thus “sparing”, the natural apple tannins to allow for slower polymerization; this
is associated with a more mellow, mature mouthfeel (The Truth About Tannins 2001).
Complications Due to Excess Tannin Additions
While tannins provide sensory attributes and protection for a cider, quality issues may
arise in the presence of high concentrations, namely tannin precipitation. Due to the
polymerization of tannins, chains increase their molecular weight and thus fall out of solution.
The product may then appear hazy or form sediment at the bottom of the container; this can
occur at many stages in the cider’s life, even if it was clear before bottling. Tannin molecules
may also react with oxygen and metals present in the cider which may produce un-welcomed
color changes; interactions with copper will create a green tint while iron reactions produce black
tints. Cider tannins also have the ability to react with acetaldehyde (ethanol); the result is a milky
haze, and due to the molecular conversion of the tannins, a thin-bodied or dull cider (The Science
of Cidermaking 1997).
Fining and the Effect on Phenolic Compounds
To prevent the over accumulation of tannins and hazing of a cider, producers will use
fining agents to remove excess tannin or particulate. Gelatin, chitosan, egg whites, or other
positively charged proteins are added to solution to bind with phenolics and ultimately
precipitate out of the cider, reducing haze and creating a more brilliant appearance. The addition
of too much protein creates a phenomenon known as “over fining,” in which a new gelatin haze
clouds the cider. For this reason, bentonite or other negatively charged atoms are added

18
simultaneously during the fining process to bind with excess gelatin while maintaining sensory
characteristics from the tannins present in the cider (The Science of Cidermaking 1997). In some
cases, fining is intentionally done to decrease phenolics and reduce bitterness or astringency.
While a significant amount of tannins are not affected by the gelatin fining treatment, the
polyphenols precipitated out of solution are known to be characteristic to the essential sensory
components of hard cider. Proanthocyanidins are most affected and are equally precipitated from
solution among most proteins used for fining. These phenolic compounds are best known for
their antimicrobial effects; this may increase the use of sulfur dioxide in hard cider to prevent
against microbial growth during storage and aging. Large molecular weight proteins are the
exception however, and precipitate fewer proanthocyanidin than other fining agents; in trade off,
it is more selective for epigallocatechin rich tannins (Sarni-Manchado 1999).
Tannin Preservation and Freeze-Drying Applications
As the primary method of obtaining experimental tannins for re-addition into hard cider,
it is important to evaluate the effect freeze-drying has on tannin and phenolic concentrations in a
raw material. Compared air-drying and freezing, freeze-drying conserved the greatest amount of
total phenolics in a variety of agricultural products: marionberries, strawberries, and corn.
Freezing displayed varying results based on pH, organic acid content, sugar concentration, initial
anthocyanidin concentration, initial cyaniding-3-glucoside content of the cultivar, and time in
season in which the commodity was processed (Asami 2003). Another study evaluating the
phenolic preservation in spearmint leaves that had undergone freeze-drying not only maintained
the highest levels of total phenolics, but also displayed the most antioxidant potency (Orphanides
2013).

19
Measuring Tannins
Currently a number of analytical techniques, based on numerous principles, are used to
evaluate total phenols, total tannins, as well as individual phenolic compounds. The use of
varying methods provides insight into different aspects involving tannin and phenolic content.
Measuring Total Phenols
Measuring total phenols refers to examining the total number of six-membered aromatic
organic compounds encompassing a variety of molecular compounds ranging from tannins to
flavonoids to phenolic acids. While analyzing total phenols does not result in a quantified
amount of each individual phenolic compound, the lower pH value of phenols in general
provides insight into acidity, bitterness, and astringency levels in hard cider.
One of the simplest methods for surveying total phenolic compounds is through
absorbency. The technique is based on benzene rings present in phenolic compounds; these rings
reflect light at 280 nm. With the use of a spectrometer, absorbance can be measured and the total
number of phenolic compounds in a sample can be estimated. Due to ease, efficiency, and
reproducibility, this technique provides numerous advantages (Lorrain 2013). Results can be
compromised as proteins, nucleic acids, and other non-phenolic compounds may possess a
benzene ring, and thus reflect light at 280 nm. These compounds cannot be distinguished from
phenolic compounds.
An additional method, the Folin-Ciocalteu assay, is based on the fundamental theory that
phenols ionize completely under alkaline conditions, provided by the Folin-Ciocalteu reagent.
Added to samples, the reagent oxidizes phenolic compounds, producing a color change from
yellow to blue; this change is observed through the use of a spectrophotometer and total phenols
is quantified. Due to the highly reactive nature of Folin-Ciocalteu reagent, non-phenolic

20
compounds such as fructose, ascorbic acid, amino acids, and bisulfite may react and skew
results. Acetaldehyde may be added to bind with bisulfite and eliminate the compound as a
possible interference; a correction may also be applied to correct for false positive results.
The iron-chloride method is rooted in the concept that phenolics with more than one
hydroxyl group will react with iron. This method strictly measures iron-reactive phenolics rather
than total phenols and thus cannot measure anthocyanins and monohydroxylated phenols. This is
generally only an issue when sampling ciders made from red apples.
Another popular technique for measuring total phenols is the enzymatic method. In the
presence of horseradish peroxidase, phenolics will convert into quinone-imine. This reaction
produces a color change; when monitored under a spectrometer, total phenols may be quantified.
While this is a new method for measuring total phenolic content, it has proven to correct well for
non-phenolic compounds when combined with Folin-Ciocalteu assay.
Measuring Total Tannins
Total tannin content, while similar to total phenolic content, provides a more detailed and
specific view of astringency and bitterness within cider. The Glories Gelatin index is based on
the precipitation of tannins in the presence of proteins, in this case, gelatin. The method relies on
spectrophotometry to quantify total tannin content after gelatin precipitation; the difference is
known as the Gelatin Index. Due to the nature of the testing and estimation techniques used in
the index, exact tannin content can only be approximated.
Resembling the Glories Gelatin Index, the Llaudy method uses protein to precipitate
tannins from solution, however ovalbumin is used in place of gelatin due to its lower sensitivity.

21
Results have proven to be more reproducible as well as correlate more closely with sensory
analysis comparisons.
The UC Davis Tannin Assay (Habertson-Adams Assay) has the capability of providing
data on many phenolic compounds including total tannin content, anthocyanins, pigmented
polymers, and non-tannin iron-reactive phenolics; for this reason it is now the standard at UC
Davis and many companies within the United States. Like the other assays, protein, in this case
bovine serum albumin (BSA), is used to precipitate tannins. Ferric chloride is then added to
solution and measured with a spectrophotometer at 510 nm (Habertson 2006).
Measuring Individual Compounds
The most accurate, as well as the most costly method, for assessing tannin content is
known as High Performance Liquid Chromatography (HPLC). The assay separates, identifies,
and quantifies individual types of compounds dissolved in solution. It is ultimately a
sophisticated take on column chromatography through the use of high pressure. The assay can
provide data on any number of compounds and is not limited to tannin structures (Kupiec 2004).

22
Chapter III – Materials and Methods
As a novel concept, the purpose of this study was to test the theory of polyphenolic
extraction from freeze-dried apple skins for addition into hard cider to further improve desired
cider qualities related to phenolics.
Hard Cider Fermentation
Five gallons of fermented, unfiltered, 100% Braeburn hard apple cider was obtained from
Bristol’s Cider House, where the cider went through a primary alcoholic fermentation using
native yeast located on the fruit, until less than 0.5 residual sugar remained. The cider then went
through a secondary malolactic fermentation using lactic acid bacteria to convert harsh malic
acid into lactic acid. This additional fermentation was carried out until there was no presence of
malic acid; the cider was aged in a neutral oak barrel.
Upon receipt, the cider was analyzed with a FOSS WineScan Auto for total phenols using
the 280 absorbance method as well as titratable acidity, ethanol content, density, malic acid
content, residual sugar, volatile acid, and color density,
Two mL aliquots from each carboy were mixed with 0.15 g of granular NaHSO3
(Spectrum Food Grade Sodium Bisulfite S1172 Lot No. 1BE1106) and added back to their
respective carboy to inhibit mold or unwanted growth; an additional 0.15g NaHSO3 was added
at a later date to maintain a 20 ppm SO2 level.
Tannin Extraction
Due to the higher concentration of total phenolics, specifically 453µg/g (Thompson
2014), Red Delicious apple skins were the variety of choice for tannin extraction. Apple skins

23
from 16.6 pounds of Red Delicious apples were peeled with a spiral peeler then freeze-dried
using a (ATLAS Freeze Drying Technology Ray 1C) to preserve phenolic content. The skins
were ground into a powder using a food processor [Cuisinart Pro Custom 11 Model DLC-8S TX
(Type 28)] to ease the extraction of phenolic compounds within the cider. The apple skins were
ground, sifted and separated from the remaining powdered flesh, then ground a second time.
Varying amounts of apple skin powder, Table 3, were added and stirred into Carboys 2-5,
with Carboy 1 acting as the control; the carboys were stored in a dry, dark storage room at room
temperature throughout testing. Samples were analyzed for total phenols, pH, titratable acidity,
ethanol content, density, malic acid content, residual sugar, volatile acid, and color density after
24 hours, 7 days, and 12 days.
Due to initially inconclusive results obtained from carboys 2-5, an additional
experimental unit, Carboy 6, consisting of the remaining amount of freeze-dried apple skins was
added; 2.5 gallons of hard cider was stirred with the respective apple skin addition, Table 3, and
left in the same conditions as carboys 1-5. Carboy 6 was sampled at 24 hours, after determining
from prior sample analyses that extraction did not continue past this time period. Statistical
analysis was conducted using JMP 11 software from SAS Institute.

24
Chapter IV – Results
Carboy 1 Carboy 2 Carboy 3 Carboy 4 Carboy 5 Carboy 6
Apple Skins
Addition (g)
0.00 1.12 2.30 5.60 11.20 18.0
Apple Skins
Concentration
(ppb)
0.00 0.059 0.12 0.30 0.59 1.9
Total Phenolics 23.913 ±
0.576b
23.910 ±
0.767b
24.192 ±
0.708ab
24.192 ±
0.363ab
24.665 ±
0.462ab
25.300 ±
0.141a
Residual Sugar
(g/100 mL)
0.044 ±
0.014c
0.057 ±
0.009c
0.094 ±
0.028c
0.062 ±
0.01bc
0.138 ±
0.056b
0.256 ±
0.006a
Table 3 - Experimental concentrations of powdered apple skin additions and physicochemical
properties in hard cider carboys. Different letters in the same row indicate a significant
difference (α≤0.05)
No significant change was observed in pH, TA, malic acid, color density, or ethanol
within each carboy over the 12 days of extraction, thus, these figures are not included. Similarly,
there was no significant difference in pH, TA, malic acid, color density, or ethanol between
Carboys 1-6 over the 12 days.
The experiment did result in significant differences in the mean total phenolics and mean
residual sugar over the 12 days of extraction between Carboys 1-6. The control, Carboy 1,
contained the least total phenolics of 23.913 ± 0.576, while Carboy 6 contained the greatest mean
total phenolics of 25.300 ± 0.141. Carboy 1 also contained the least amount of RS, 0.044 ±
0.014, while Carboy 6 contained the most with a significant increase of 0.256 ± 0.006 RS.
Despite this overall increase in RS with the increase in apple skin additions, the RS decreased
between Carboys 3 and 4 then steadily increased again from Carboys 4 to 6.

25
While color density proved to not be statistically different between the carboys, visible
changes in cider color were noted, with Carboy 1 being a hay color and Carboy 6 having more
brown and red notes.
No significant difference in extraction rate was seen between the 24 hour, 7 day, and 12
day sampling intervals.
Chapter V – Discussion
Concentration of Apple Skins
Initial concentrations of apple skins to hard cider, Carboys 2-5, proved to be
insufficiently high enough to produce statistically significant results in any of the
physicochemical property tests performed. As a consequence, an additional, highly concentrated,
1.9 ppb, experimental unit, Carboy 6, was added. Carboy 6 proved to be of high enough
concentration to see significant differences in total phenolics as well as residual sugar.
Concentration proved to not be of affect regarding the length of time of extraction, as no
significant differences could be seen between hour 24 and day 7 or 12. This suggests that all
components within the apple skins are extracted within 24 hours, and thus the treatment may be
applied in a quick and efficient manner.
Total Phenolic Extraction
When evaluating the extraction of phenolic compounds from freeze-dried apple skins into
hard cider it is imperative to consider the type of phenolic compounds and the methods and rates
of extractions for each component. As Kennedy (2003) summarized, anthocyanins are much
smaller in size than the tannins, and therefore, will diffuse more rapidly. Additionally,
anthocyanins are structurally different than tannins, which may lead to diffusion differences.

26
These differences are imperative to keep in mind as the samples in this study were evaluated
using the 280 nm absorbance method in which only total phenolic compounds were measured
and not individual phenolic compounds. For this reason, the total tannin extraction yield can only
be estimated.
Given the visible color differences between the experimental cider units, in addition to
the knowledge that anthocyanins extract at greater rates than tannin compounds, it is surprising
to see no significant differences in color density between varying apple skin concentrations.
Future research may consider the use of HPLC to both identify and quantify specific phenolic
compounds extracted from freeze-dried apple skins as well as additional methods of evaluating
color changes within hard cider.
Alcohol content also has an effect on the rate and yield of extraction. Anwar (2012)
found 80% ethanol and 100% methanol to be the optimal solvents for extracting antioxidant
components. The cider used in this study was 8.45 v/v% alcohol, and while slightly higher than
most hard ciders presently on the market, the alcohol concentration is not in an ideal range for
extraction purposes. Future experimentation may consider the use of either methanol or ethanol
solvents to extract apple skin phenolics at a greater rate or independent of the hard cider matrix
for addition at a later time.
Residual Sugar
One side effect of the addition of freeze-dried apple skins proved to be an increase in
residual sugar. This increase could be due to the tendency of alcohol to diffuse into the apple
skins and sugar to diffuse out of the fruit and into the aqueous cider phase. In addition, ethanol,
as a zwitterion, can readily dissolve polar compounds, such as the glucose and fructose found in
apples and apple skins, allowing these sugars to be incorporated easily into the cider.

27
The significant increase in residual sugar has the potential to change many characteristics
of cider including the perceived astringency of tannins as well as perceived acid. The interaction
of tannins, acid, and residual sugar provide the characteristics and complexity of notable ciders
and thus must be considered when applying the experimental treatment.
Sensory
When evaluating the sensory components of different ciders, the effect of tannins on the
overall flavor of the cider must be taken into account. Polyphenols are characterized by hydroxyl
groups which have the ability to bind to salivary proteins, causing the astringency associated
with cider tannins (Lea 1978).
Initial experiment plans included a sensory analysis of the varying carboys to determine
the organoleptic effect of extracting tannins from freeze-dried apple skis. Due to the effects of
malolactic fermentation, the aroma of the cider was severely tainted; mousiness and mildew
overwhelmed the cider, creating an impractical and unpleasant tasting experience. These
characteristics were noticed before the apple skin addition.
Conclusion
Based on the current experiment and literary research, freeze-dried apple skins have
shown to contribute sufficient polyphenols to hard cider with the goal of enhancing desired cider
qualities in addition to the ability to provide notable amounts of residual sugar.
Future Research
To further determine the effectiveness of apple skin additions on the quality and other
sensory attributes of hard cider, future research should include ciders made from various regions

28
and from different varietals to account for variances in flavor and chemical components of the
cider. Cider that has not undergone complete malolactic fermentation should also be used in
future studies to result in a product that is palatable enough to detect differences in other sensory
attributes such as astringency, bitterness, and improved overall quality.
Additional experimentation should be completed to more precisely pinpoint the proper
concentration of apple skins to be added to the cider to achieve the desired effects. Further
studies should also determine the time it takes to fully extract the polyphenols from the apple
skins in order to maximize efficiency as well as to explore the potential of freeze-dried apple
skins as an additive in improving or darkening color within hard ciders.
Kashyap (2000) explains that enzymes such as pectinase break down complex
polysaccharides of plant tissues into simpler molecules, like galacturonic acids. The role of
acidic pectinases in bringing down the cloudiness and bitterness of fruit juices is well
established. Additional studies may be centered on the various treatments of the freeze-dried
apple skins to simplify the apple skin matrix and ease phenolic content extraction, while
simultaneously creating acidic pectinases to reduce clouding in cider.

29
References
Alberto, M., Canavosio, M., Manca de Nadra, M. 2006. Antimicrobial effect of polyphenols
from apple skins on human bacterial pathogens [ISSN: 0717-3458]. 9(3): 205-209. Available
from [scielo.cl]. Posted 2006. Form of citation in text: (Alberto 2006)
http://www.scielo.cl/pdf/ejb/v9n3/a06.pdf
Alcoholic Drinks – January 2015 Overview of New Product Launches. [Internet]. Euromonitor
International. Feb 11, 2015. [Accessed 2015 Jan 30]. Available from [euromonitor.com] Form of
citation in text: (Euromonitor New Product Launches 2015)
http://blog.euromonitor.com/2015/02/alcoholic-drinks-january-2015-overview-of-new-product-
launches.html
Anwar, F., Przybylski, R. 2012. Acta Sci. Pol., Technol. Aliment. 11(3): 293-301. [Accessed
2015 June]. Available from www.food.actapol.net. Form of citation in text: (Anwar 2012).
http://www.food.actapol.net/pub/9_3_2012.pdf
Apple Nutrition [Internet]. Fearn, U. 2005. [Accessed 2015 Jan 30]. Available from: nutri-
ception.co.uk. Form of citation in text: (Apple Nutrition 2005) http://www.nutri-
ception.co.uk/office/documents/pdf/NCF0101.pdf
Asami, D., Hong, Y., Barret, D., Mitchell, A. 2003. Comparison of the total phenolic and
ascorbic acid content of freeze-dried and air-dried marionberry, strawberry, and corn grown
under conventional, organic, and sustainable agricultural practices. J Agric Food Chem. 51(5):
1237-1241. Available from pubmed.gov. Form of citation in text: (Asami 2003).
http://www.ncbi.nlm.nih.gov/pubmed/12590461
Ashok, P.K., Upadhyaya, K. 2012. Journal of Pharmacognosy and Phytochemistry: Tannins are
Astringent [ISSN 2278- 4136]. 1(3): 45-50. Available from phytojournal.com. Form of citation
in text: (Ashok 2012) http://www.phytojournal.com/vol1Issue3/Issue_sept_2012/8.1.pdf
Chemistry World: Fermenting Ideas [Internet]. Exeter, UK: Extance, A.; 2014 [Accessed 2015
Feb 13]. Available from rsc.org. Form of citation in text: (Chemistry World 2014)
http://www.rsc.org/chemistryworld/2014/12/fermenting-ideas-cider-chemistry
The Cider Journal. 2015. Hard Cider Sales Grow by 71% in 2014. The Cider Journal [serial
online]. Available from ciderjournal.com. Posted Jan 12, 2015. Form of citation in text: (Cider
Journal 2015) http://ciderjournal.com/hard-cider-sales-grows-71-2014/
Cidermaking on the Farm [Internet]. Bulletin No. 2. Long Ashton, Bristol, UK.: National Fruit
and Cider Institute; 1934. [Accessed 2015 Jan 30]. Available from cider.org.uk. Form of citation
in text: (Cidermaking on the Farm 1934) http://www.cider.org.uk/farm.htm
Cider/Perry in the US [Internet]. Euromonitor International. Jul, 2014. [Accessed 2015 Jan 30].
Available from euromonitor.com. Form of citation in text: (Euromonitor 2014)
http://www.euromonitor.com/cider-perry-in-the-us/report

30
The Cider Press: Cider Styles. [Internet]. 2011. [Accessed 2015 Jan 28]. Available from
http://drinks.seriouseats.com/2011/01/the-cider-press-cider-styles.html. Form of citation in text:
(The Cider Press 2011).
Guyot, S., Doco, T., Souquet, JM., Moutounet, M., Drilleau, JF. 1997. Characterization of highly
polymerized procyanidins in cider apple (Malus sylvestris var. kermerrien) skin and pulp.
Sciencedirect [serial online]. 44(2): 351–357. Available from sciencedirect.com. Form of citation
in text: (Guyot 1997)
http://www.sciencedirect.com.ezproxy.lib.calpoly.edu/science/article/pii/S0031942296004803
Guyot, S., Le Bourvellec, C., Marnet, N., Drilleau, J.F. 2002. Procyanidins are the most
Abundant Polyphenols in Dessert Apples at Maturity [serial online]. 35(3): 289–29. Available
from sciencedirect.com. Posted May 2002. Form of citation in text: (Guyot 2002)
http://www.sciencedirect.com/science/article/pii/S0023643801908436
Guyot, S., Marnet, N., Laraba, D., Sanoner, P., Drilleau, JF. 1998. Reversed-Phase HPLC
following Thiolysis for Quantitative Estimation and Characterization of the Four Main Classes of
Phenolic Compounds in Different Tissue Zones of a French Cider Apple Variety (Malus
domestica Var. Kermerrien) [serial online]. 46(5): 1698–1705. Available from pubs.acs.org.
Posted May 1, 1998. Form of citation in text: (Guyot 1998)
http://pubs.acs.org/doi/abs/10.1021/jf970832p
Guyot, S., Marnet, N., Sanoner, P., Drilleau, JF. 2003. Variability of the Polyphenolic
Composition of Cider Apple (Malus domestica) Fruits and Juices [serial online]. 51(21): 6240–
6247. Available from pubs.acs.org. Posted Sep 6, 2003. Form of citation in text: (Guyot 2003)
http://pubs.acs.org/doi/abs/10.1021/jf0301798
Harbertson, J., Spayd, S. 2006. American Journal of Enology and Viticulture.57(3): 280-288.
Available from wineserver.ucdavis.edu. Form of citation in text: (Habertson 2006).
http://wineserver.ucdavis.edu/pdf/attachment/45%20%20winery%20methods%20for%20phenols
%20.pdf
Harte, J., Popa, D. 2002. Cider Making from Traditional to Modern [serial online]. Available
from productcenter.msu.edu. Form of citation in text: (Harte and Popa 2002)
http://productcenter.msu.edu/uploads/files/makecider.pdf
Heikefelt, C. 2011. Chemical and sensory analyses of juice, cider and vinegar produced from
different apple cultivars. SLU Horticultural Science Programme. [Accessed 2015 Jan 30].
Available from: [stud.epsilon.slu.se]. Form of citation in text: (Heikefelt 2011)
http://stud.epsilon.slu.se/2481/1/heikefelt_c_110415.pdf
The Homebrew Helper [Internet]. Shabatura, J.; 2014. [Accessed 2015 Feb 23]. Available from
howtomakehardcider.com. Form of citation in text: (Homebrew Helper 2014)
http://www.howtomakehardcider.com/rack-bottle.html

31
Janik, Erika. 2011. Apple: A Global History. United Kingdom: Reaktion Books Ltd. p.134. Form
of citation in text: (Janik 2011). http://site.ebrary.com/lib/calpoly/reader.action?docID=10520510
Kashyap, D., Vohra, P., Chopra, S., Tewari, R. 2000. Applications of pectinases in the
commercial sector: a review. Bioresource Technology. 77(3):215–227. Available from
sciencedirect.com. http://www.sciencedirect.com/science/article/pii/S0960852400001188. Form
of citation in text: (Kashyap 2000).
Kennedy, J. Gahons, C. Fresno State University. 2003. Phenolic Extraction in Red Wine
Production. San Rafel, CA: Practical Winery and Vineyard. Available from
https://www.fresnostate.edu/jcast/ve/documents/outreach/Phenolic-page%2038.pdf. Form of
citation in text: (Kennedy 2003).
Kupiec, T. 2004. International Journal of Pharmaceutical Compounding 8(3): 223-227. Available
from arlock.com. Form of citation in text: (Kupiec 2004). http://arlok.com/articles/High-
Performance%20Liquid%20Chromatography.pdf
Lea, A., Arnold, G. 1978. The Phenolics of Cider: Bitterness and Astringency. Journal of
Science of Food and Agriculture. 29: 478-483. Available from readcude.com. Form of citation in
text: (Lea 1978).
http://www.readcube.com/articles/10.1002%2Fjsfa.2740290512?r3_referer=wol&tracking_actio
n=preview_click&show_checkout=1
Lees, G., Suttill, N., Wall, K., Beveridge, T. 1995. Localization of condensed tannins in apple
fruit peel, pulp, and seeds. Canadian Journal of Botany [serial online]. 73(12): 1897-1904.
Available from nrcresearchpress.com. Form of citation in text: (Lees 1995)
http://www.nrcresearchpress.com/doi/abs/10.1139/b95-202#.VOy-H_nF91b
Lorrain, B., Ky, I., Pechamat, L., Teissedre, P. 2013. Evolution of Analysis of Polyphenols from
Grapes, Wines, and Extracts. Molecules. 18: 1076-1100. Available from mdpi.com. Form of
citation in text: (Lorrain 2013). http://www.mdpi.com/1420-3049/18/1/1076
Mainstream Cidermaking [Internet]. U.K.: Lea, A.G.H.; 1995. [Accessed 2015 Jan 30].
Available from cider.org.uk. Form of citation in text: (Mainstream Cidermaking 1995)
http://www.cider.org.uk/abridge.htm
Microbiology Faculty. 2015. 421 Food Microbiology Laboratory Manual. California Polytechnic
State University, San Luis Obispo, CA: Cal Poly University Store. p 75. Form of citation in text:
(Micro Manual 2015)
Orphanides A., Goulas V., Gekas V. 2013. Effect of drying method on the phenolic content and
antioxidant capacity of spearmint. Czech J. Food Sci., 31: 509–513. Available from
agriculturejournals.cz. Form of citation in text: (Orphanides 2013).
http://www.agriculturejournals.cz/publicFiles/100559.pdf

32
The Real Cider and Perry Page: Cider Making [Internet]. Original text copyright Gillian Grafton
1990-1996; revisions copyright Paul Gunningham 2003. [Accessed 2015 Jan 30]. Available
from: [homepage.ntlworld.com] Form of citation in text: (Grafton 1996)
http://homepage.ntlworld.com/scrumpy/cider/cider.htm
Renard, C. Dupont, N. Guillermin, P. 2007. Concentrations and characteristics of procyanidins
and other phenolics in apples during fruit growth. Phytochemistry [serial online]. 68(8): 1128–
1138. Available from sciencedirect.com.ezproxy.lib.calpoly.edu. Form of citation in text:
(Renard 2007)
http://www.sciencedirect.com.ezproxy.lib.calpoly.edu/science/article/pii/S0031942207000957
Sarni-Manchado, P., Deleris, A., Availone, S., Chynierand, V., Moutounet, M. 1999. Analysis
and Characterization of Wine Condensed Tannins Precipitated by Proteins Used as Fining Agent
in Enology. 50(1): 81-86. Available from ajevonline.org. Form of citation in text: (Sarni-
Manchado 1999). http://www.ajevonline.org/content/50/1/81.short
The Science of Cidermaking [Internet]. U.K.: Lea, A.G.H.; 1997. [Updated: 2009, Accessed
2015 Jan 30]. Available from cider.org.uk. Form of citation in text: (The Science of Cidermaking
1997) http://www.cider.org.uk/part5.htm
Scott Laboratories [Internet]. Scott Laboratories, Inc.; 2010. [Accessed 2015 Feb 20]. Available
from scottlab.com. Form of citation in text: (Scott Lab 2010) http://www.scottlab.com/products-
106.aspx#time
State of the Craft Beer Industry [Internet]. San Francisco, CA: Demeter Group Investment Bank;
2013. [Accessed 2015 Jan 30]. Available from demetergroup.net. Form of citation in text: (State
of Craft Beer Industry 2013) http://demetergroup.net/sites/default/files/news/attachment/State-of-
the-Craft-Beer-Industry-2013.pdf
Tannin in Cider Apples [Internet]. U.K.: Lea, A.G.H.; 1995. [Accessed 2015 Jan 30]. Available
from cider.org.uk. Form of citation in text: (Tannin in Cider Apples 1995)
http://www.cider.org.uk/tannin.htm
Thompson-Witrick, K., Goodrich, K., Neilson, A., Hurley, E., Peck, G., Stewart, A. 2014
Characterization of the Polyphenol Composition of 20 Cultivars of Cider, Processing, and
Dessert Apples (Malus × domestica Borkh.) Grown in Virginia. Journal of Agricultural and Food
Chemistry [serial online]. 62(41): 10181–10191. Available from pubs.acs.org. Posted Sep. 17,
2014. Form of citation in text: (Thompson 2014) http://pubs.acs.org/doi/abs/10.1021/jf503379t
Treutter, D. 2001. Biosynthesis of phenolic compounds and its regulation in apple. Plant Growth
Regulation [serial online]. 34: 71-89. Available from link.springer.com. Form of citation in text:
(Treutter 2001) http://link.springer.com/article/10.1023%2FA%3A1013378702940#page-2
The Truth About Tannins [Internet]. 2001. Wine Tasting, Vineyards, in France. [Accessed 2015
Feb 20]. Available from wineterroirs.com. Form of citation in text: (The Truth About Tannins
2001) http://www.wineterroirs.com/the-truth-about-tannins.html

33
UC Davis Waterhouse Lab: Volatile Acidity [Internet]. UC Davis, Sacramento, CA: Neeley,
Ezekeil; 2004. [Accessed 2015 Feb 23]. Available from [waterhouse.ucdavis.edu]. Form of
citation in text: (UC Davis 2004) http://waterhouse.ucdavis.edu/whats-in-wine/volatile-acidity
Using Fining Agents [Internet]. Winemaker Magazine; 2002. [Accessed 2015 Feb 25]. Available
from winemakermag.com. Form of citation in text: (Winemaker 2002).
https://winemakermag.com/715-using-fining-agents-techniques
Volatile Acidity and Oxidation [Internet]. Surry Community College: Kelly, M.; 2011.
[Accessed 2015 Feb 23]. Available from wine.appstate.edu. Form of citation in text: (VA and
Oxidation 2011)
http://wine.appstate.edu/sites/wine.appstate.edu/files/Volatile%20Acidity%20Kelly%202011.pdf
Watson, E. 1973. Tannins in Fruit Extracts as Affected by Heat Treatments [serial online]. 2(2):
112-8. Available from online library.wiley.com. Posted Jul 3, 2009. Form of citation in text:
(Watson 2009) http://onlinelibrary.wiley.com/doi/10.1177/1077727X7300200204/abstract
Ye, M., Yue, T., Yuan, Y. 2014. Changes in the profile of volatile compounds and amino acids
during cider fermentation using dessert variety of apples. European Food Research and
Technology. Available from link.springer.com.ezproxy.lib.calpoly.edu. Posted March 28, 2014.
Form of citation in text: (Ye 2014)
http://link.springer.com.ezproxy.lib.calpoly.edu/article/10.1007/s00217-014-2204-1/fulltext.html

Senior Project

Recommended

Recommended

More Related Content

What's hot

What's hot (15)

Viewers also liked

Viewers also liked (14)

Similar to Senior Project

Similar to Senior Project (20)

Senior Project