Alcoholic Beverages IV

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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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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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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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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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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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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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

Alcoholic Beverages IV

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