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Department of Post-Harvest Management
Advisor : Chala Gowe (MSc)
June, 2018
Jimma, Ethiopia
By: Kumsa Negasa

2.  Introduction
 Objectives of the review
 Body of the seminar
 Summary
 Recommendation
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3. 1.1 Background of the review
 Wine is an alcoholic beverage made from grape fermented
without the addition of sugars, acid, enzymes, water, or other
nutrients (Johnson ,2000)
 It has been produced for thousands of years.
 The earliest known traces of wine are from Georgia in 6000 BC.
 It has always been recognized that wine quality is related to the
quality of the fruit(Arribas et al ,2005)
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4.  The quality of grape berries is one of the factors in controlling
wine quality.
 In addition to grape quality, Fermentation conditions are one of
the critical factors on the quality of wine.
 Wine fermentation is one of the most ancient of human’s
technologies and is now one of the most commercially
prosperous biotechnological processes (Arribas et al ,2005)
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5. 1.2.1 General Objectives
To review effect of fruit wine quality and fermentation
conditions on the quality of wine
1.2.2 Specific Objectives
To review effect of Initial quality of fruits wine on wine
quality
To review factors influencing fermentation and wine quality
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6. 2.1. Initial quality of grape fruits and wine quality
 The quality of grapes, as well as wine quality, flavor, stability,
and sensorial characteristics depends on the content and
composition of several different groups of compounds from
grapes.(Goldiner ,et.al 2009)
 The composition and quality of grapes could be influenced
synergistically by species, vineyard location, ripeness and
seasonal variation ( Wine Searcher , 2014).
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7. 2.1.1 Species of grapes and Vineyard Location
 Different grape products require different characteristics of
grapes, which drives the cultivation of new species (Soejima, &
Wen,2006)
 The best species of grapes for wine making are Andrell and
Maquette species.
 Vines of Arandell are moderately cold-resistant, and upright
growth of Arandell makes it suitable for vine management.
(Rachel ,2012)
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8. Environmental factors such as climate, soil condition, and other
environmental conditions would influence the composition of
grape (Soejima, & Wen,2006)
The cold climate will intervene respiration of vine, which causes
excess accumulated organic acid and undesirable low pH value
(Rachel, 2012.
The water status significantly influence grape vine and fruit quality
as well.
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9. 2.1.2 Ripeness of Grape
 At a different stage of ripening, the various combinations of
aromas, flavors, tannins, sugar and acids result in unique
characters.
 Grape skin loses chlorophyll and begins to :
synthesize and
accumulate phenolic compounds responsible for characteristic
colors: yellow-gold (flavonols) and pink and red
(anthocyanins) (Hellman et.al,2014).
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10. As time advances, the sugar content of the berries increases,
acidity level drops and pH increases.
The changes in the tannins advances as well, which makes the
grape less bitter-tasting and softer( wine anorak ,2015).
As the berries proceed to full maturity, berries size reaches the
maximum, and sugar accumulation rate becomes slow.
The complexity of aroma and flavor increases during the later
stage of ripening.
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Figure 1. Generalized graphical representation of grape berry compositional
changes during development and ripening (From Hellman, E. 2014)

12. 2.1.4 Seasonal Variation
 The impact of seasonal variation of climate would result in
different
harvest time,
fluctuated grape sugar, and
acid concentrations.
Those changes lead to discrepancies of wine alcohol levels,
acidities, and modification of aroma compounds (De Orduna,2010)
For example, hot temperatures would inhibit metabolite
accumulations, which may affect wine aroma and color.12

13. 2.2.1 Effect of Temperature on Fermentation
 Controlled temperature is important for the production of fine
wines.
 Its influence begins when the grapes are ripening, and continues
during fermentation and aging of the wine ( Robinson ,2006)
 Even high-quality grapes of the best varieties may not result in
fine wines if the proper temperature is not maintained during the
wine-making process (Akubor,et.al,2013)
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 High-temperature control in wine making is important
because:
 fermentation becomes sluggish, and at about 100°F it
stops.
 At these high temperatures, problems arise with growth of
Lactobacillus sp. and toxic products of the yeast.
 Alcohol losses are also greater and yields are lowered.
 The aromas and flavors of white wines decrease with
increasing fermentation temperatures (Kumaret.al, 2008).

15. o Low-temperature control is also necessary because:
 At temperatures below 50°F (10°C) yeast growth and rate
of fermentation are extremely slow.
 Red wine fermentation should be above 65°F (18°C) for best
color and flavor results (Fleet, 2013)
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16.  In general, temperature control during alcoholic fermentation is
necessary to facilitate
 yeast growth,
 extract flavors and colors from the skins,
 permit accumulation of desirable by-products, and
 prevent undue rise in temperature that might kill the yeast
cells (Fleet, 2013)
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17. 2.2.2 Effect of pH and acidity on Fermentation
The pH plays an important role in aging, clarifying, or fining.
As the strength of the relative charge of suspended particles
decreases in the wine, the pH of the wine increases.
At high pH, organic protein fining agents may possess a positive
charge insufficient to bind to the negatively charged particulates,
thus potentially increasing the turbidity of the wine.
This phenomenon is called “over fining (Nuengchamnong et.al
,2017)17

18. The traditional process of fermentation involves extracting
fruits juice and adjusting the pH to 4.0 using sodium
bicarbonate and adding yeast nutrient (ammonium phosphate)
at 0.14 g/l (Steinkraus,1992).
A pH level of 4.0 may be conducive for the development of
unwanted microbes like Leuconostoc oenos
This can be prevented by controlling the pH by reducing the
wine pH to below 3.2 (Meyer et.al ,2017).
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19.  Wines produced from grapes in warmer climates tend to be less
acidic (pH > 3.5) and a further reduction in acidity may have
adverse effects on the quality of the wine.
 Decreasing the acidity also increases the pH to values which
can allow spoilage organisms like Leuconostoc oenos to
multiply to embark on malolactic fermentation (Wu et.al 2013).
 Acids present in wine enhance the taste, aroma, and
preservative properties of the wine.
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20. 2.2.3 Effect of Sugar Content on Fermentation
Sugar is the main substrate for fermentation of fruits juice into
alcohol (Keller,2010).
According to Hui (Huiet al.,1994) sugars are the most common
substrate of fermentation to produce ethanol, lactic acid, and
carbon dioxide.
Although sugar is an important substrate of fermentation,
higher sugar concentration inhibits the growth of
microorganisms (Pino& Queris,2015)20

21. At concentrations higher than 40% of sugar content only a
certain group of yeasts the Osmophilic type can survive.
There are only a few yeasts that can tolerate sugar
concentrations of 65–70% and these grow very slowly in these
conditions
A winemaker who wishes to make a wine with high levels of
residual sugar (like a dessert wine) may stop fermentation early
o by dropping the temperature of the must or
o Adding a high level of alcohol (like brandy) to the must21

22. 2.2.4 Effect of Microorganisms on Fermentation
 There have been several researches to identify the
microorganisms involved in fruits fermentation.
 The microorganism responsible for grape and other fruit wine
fermentation is S. cerevisiae. (Davis &Noble,1995).
 Yeast is a unicellular fungus which reproduces asexually by
budding or division, especially the genus Saccharomyces which
is important in food fermentations has the ability to reproduce
much faster (Keller,2013).22

23.  The cultured yeasts most commonly used in winemaking
belong to the S. cerevisiae(also known as sugar yeast”) species.
 Some yeast strains are chromogenic and produce a variety of
pigments, including green, yellow, and black.
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24.  Within this, species are several hundred different strains of
yeast that can be used during fermentation to affect the heat or
vigor of the process and enhance or suppress certain flavor
characteristics of the wine.
 Yeast, in general, has a natural protein removal effect during
fining or clearing.
 It is important to rack the wine soon after yeast fining to avoid
reductive aromas (Rotter,2008)
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25. 3.1 Conclusion
 Fruit wines are undistilled alcoholic beverages usually made from
grapes or other fruits such as peaches, plums, or apricots, banana,
and elderberry
 The nutritive value of wine is increased due to the release of
amino acids and other nutrients from yeast during fermentation.
 Wine quality depends on the vinification process and the
geographical origin of the grapes
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26.  The fermentation of wine grapes affected by efficiency of
particular yeast strain, sugar content, pH, temperature, etc.
 Temperature plays an extremely vital role in the fermentation
process.
 If the fermentation temperature is too cool, the yeast may not be
invigorated enough to ferment.
 Optimization of the temperature and proper selection of yeast are
the major important factor for production of high quality of wine
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27.  Based on the review I recommended the following points for
the wine makers to minimize the loss of wine quality due to
fermentation condition and fruit wine selection
Physically damaged, mould and insect affected should be
avoided
Selective hand picking and harvesting only matured grape is
very important
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28. Excessive nitrogen addition, especially late in fermentation,
should be avoided as excess N2 can become a substrate for
later unwanted microbiological activity which might result in
a marked reduction of wine quality.
In general all the fermentation conditions and fruit wine
selection should have to get a great care and attention to
obtain high quality of wines
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The end