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8/13/2019 Alcoholic Beverages IV
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Food Microbiology II- NFSC 278
Industrial Microbiology
The Microbiology of
Alcoholic Beverages IV
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Microorganisms in the Beer
Process
Microbial growth on barley kernels if not
controlled at pre-harvest, post-harvest and
malting stages can produce metabolites thataffect:
- malt quality
- progress of the alcoholic fermentation
- beer quality
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Microorganisms in the Beer
Process
Some general problems that have been related
to the microbiology of barley and malt include:
- inconsistent germination of barley kernels
- giving malt of decreased quality
- malt with increased protein degradation and
increased levels of amino acids- off-flavors in beer
- instability of dissolved carbon dioxide
- presence of mycotoxins in beer
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Microorganisms in the Beer
Process
Beer that gushes :
characterized by sudden eruption of gas,foam and liquid on opening bottled or canned
beer
linked to the production of polypeptides and
peptido-glycans by the growth of molds during
malting and pre-malting stages
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Microorganisms in the Beer
Process
Delays in hygiene in handling the wort during
mashing or after boiling will cause
microbiological problems
Thermo-tropic-spore-formers of Baci l lus (B.
stearothermophi lus) and Clost r id ium present as
contaminants of the malt are capable of growth attemperatures of mashing
This results in acidification and off-flavors in the
wort through the production of lactic and butyric
acids
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Microorganisms in the Beer
Process
Boiled wort is a nutritious medium and will
support the growth of a wide range of bacterial
species
Growth of bacteria in the wort gives beer off-flavors and impact subsequent growth of yeast
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Microorganisms in the Beer
Process
Fermentation is initiated by inoculating the wort
with desired strain of S. cerevis iae to give a
starting population of about 15x106CFU/ml
Yeast cells from a previous fermentation may be
harvested and re-utilized
The practice of recycling the yeast is quitecommon and the cells may be used for up to 5-8
fermentations before they lose significant activity
and have to be replaced by propagating a new
batch
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Microorganisms in the Beer
Process
For re-use, yeast cells are taken at the end of
fermentation, washed to remove dead cells andsedimented wort material and then stored as a
concentrated slurry at 0-5oC
Quality assurance checks are needed to verify
the recycled yeasts retain good viability and
fermentative activity and are not contaminated
with unacceptable levels of bacteria or wild
yeasts
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Flavor Maturation and Finishing
Maturation generally involves storing the
beers at 2-5oC for one to several weeks
To decrease the time of maturation, beer is
purged with carbon dioxide
Reduction in the concentration of diacetyl,which gives an undesirable buttery flavor to
the beer, is the main rate-limiting step
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Beer Spoilage
Few microorganisms can tolerate the relatively
hostile environmental conditions of beer
(alcohol, hop constituents, few nutrients, low pHof 4.0-4.5)
Critical steps in beer processing are:
- Bulk storage of beer during maturation
- Beer packaged in kegs and barrels
- Taps and pipes used for beer transfer and
dispensing
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Beer Spoilage
Lactobaci l l iand Pediococc i are particularly
troublesome in beer during maturation and after
packaging
Lactobaci l l icause a silky turbidity of the product
and buttery acid off-flavors
Pediococc iproduce acid + a strong butteryaroma due to diacetyl formation and ropiness due
to extracellular slime formation
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Beer Spoilage
Exposure of beer to oxygen will encourage the
growth of acetic acid bacteria that oxidize ethanol
to acetic acid giving off-flavors as well as causingturbidity and ropiness
Growth of any yeast other than the desired strain
during maturation or any yeast after packaging of
the beer, will lead to off-flavors and turbidity
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Distilled Alcoholic
Beverages
Distilled products (spirits) represent a
substantial proportion of the market for alcoholic
beverage
Because of distillation, these products are
substantially enriched in their content of ethanol
Spoilage by microorganisms should not aproblem for these products
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Distilled Alcoholic
Beverages
They are categorized into two groups:
1- Represented by those beverages where the
raw material has an important influence on thesensory quality of the final product
E.g. Whisky: derived from cereals
Rum: produced from cane sugar ormolasses
Brandies and wine spirits: distilled from
fermented juices of grapes and other fruits
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Distilled Alcoholic
Beverages
2- Includes products such as gin, vodka, anis,
ouzo which consist of a distilled alcohol base that
has been processed to give specific flavorcharacteristics
The contribution of microorganisms to the
production of these beverages is largely confined
to the alcoholic fermentation