2. INTRODUCTION
Fermentation process is defined as a desirable process of biochemical
modification of primary food matrix brought about by microorganisms and
their enzymes
Fermented foods and beverages are the products that have been subjected to
the desirable biochemical changes which lead to a general improvement in the
shelf life, texture, taste and aroma, nutritional value and digestibility of cereal
products.
3. CONTINUATION…
Beer, like any other fermented food, is an immutably microbial product which
is made up of major portion of a cereal namely barley. Microbial activity is
involved in every step of its production, defining the many sensory
characteristics that contribute to final quality.
4. THE INVOLVEMENT OF THE MICROORGANISMS
IN THE FERMENTATION PROCESS (STARTER
CULTURE)
The basic cereal fermentation process involves the enzymatic activities of
lactobacilli, leuconostoc, pediococci, yeasts and moulds
Yeast is one of the microorganism (starter culture) that is responsible for
aerobic fermentation in beer
Fermentation of cereal extracts by Saccharomyces is the most important
microbial process involved in brewing, a vast array of other microbes affect the
complete process
Microbial interdiction at every step of the barley-to-beer continuum greatly
influences the quality of beer
5. CONTINUATION…
The dominant types of yeast used to make beer are the top-fermenting
Saccharomyces cerevisiae and bottom-fermenting Saccharomyces uvarum.
Brettanomyces ferments lambics, and Torulaspora delbrueckii ferments
Bavarian weissbier.
NOTE: Today there is the reclassification of Saccharomyces species (both the top-
fermenting Saccharomyces cerevisiae and bottom-fermenting Saccharomyces
uvarum) which are considered to be members of S. cerevisiae
6. YEAST GROWTH IN THE MEDIA
AND ITS NUTRIENT REQUIREMENT
Malted barley is the main ingredient, which, when milled and heated in water
to extract its nutrient, provides a nourishing sugar and protein- rich solution
named wort which is an ideal medium in which yeast may grow and ferment
Yeast cells will grow on a minimal medium containing dextrose (glucose) as a
carbon source and salts that supply nitrogen, phosphorus, and trace metals
Yeast cells grow much more rapidly in the presence of rich medium that
contains reagents such as yeast extract and bactopeptone
7. INTERACTION OF YEAST WITH
OTHER MICROORGANISMS
Brewing microbiology begins in the barley field, where plant-microbial
interactions and the microbiological status of the grain both pre- and
postharvest can have serious implications for brewhouse processing and beer
quality.
Although these microbes do not survive the malting and brewing processes,
secretory factors may persist, affecting downstream quality.
During the mashing of malt, some of the thermotolerant microbes, remain
active in the nutrient-rich and high-moisture environment
Bacterial growth during this stage have beneficial consequences, and mash
acidification by lactic acid bacteria improves the extraction, fermentability, and
nitrogen yield of wort which is an ideal environment for the growth of yeast.
8. A diverse set of microbes has been detected on barley but only a few plant-
pathogenic fungi have notable relevance to beer quality. Fusarium spp. and
several other fungal pathogens of barley and other cereals are capable of
producing mycotoxins that survive the brewing process and can be detected in
finished beer.
A number of mycotoxins have been detected in barley, including
deoxynivalenol
9. STARTER CULTURE FAILURE
In wine and beer production, yeast as a starter culture is used to ferment the
product (Barley wort) to alcohol. The alcohol preserves the product.
Due to the failure of the starter culture, the process of fermentation is retarded
or even eliminated completely
This results into high oxygen, nutrient content as well as low antimicrobial
compounds hence creating an ideal environment for the growth of spoilage
microorganism.
Therefore, the safety and shelf life of the product is compromised
10. BIOCHEMICAL PRODUCTS GENERATED
AND THEIR INTERACTION WITH
NUTRIENTS
Ethanol and carbon dioxide are produced during the conversion of the wort to
beer through the fermentation of maltose and other sugars.
Bacterial growth for example, Bacillus spp, can cause excessive acidification
and nitrosamine formation by reduction of nitrate to nitrite
high concentrations of the mycotoxins produced by fungi inhibit yeast growth
during beer fermentation
11. SAFETY AND SHELF LIFE OF THE
FINAL YEAST FERMENTED PRODUCT
Beer is high in ethanol and carbon dioxide, contains hop-derived antimicrobial
compounds, and is low in pH, oxygen, and residual nutrients which results in
conditions that are hostile to the growth of most microorganisms as well as
supporting potential microbial spoilage
This reduces the rate of spoilage hence increasing the shelf life of the product
as well as guaranteeing its safety.
12. However, fungal infection of barley causes a problem with more immediate
consequences to the consumer: gushing.
This is caused by hydrophobic fungal peptides (hydrophobins), which serve as
nucleation sites for CO2 bubbles in beer, resulting in the spontaneous release
of gas and over foaming once the container is opened
