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Quality control for microbreweries; keeping micro-organisms at bay.

Quality Control For Microbreweries

Keeping micro-organisms at bay.

Most beer defects are caused by microrganisms. These microorganisms can affect all brewing steps and damage the quality of beer. The larger breweries have long had established quality control and quality assurance programs. Since widespread inconsistency among micro-brewed beers could detract from the strength of the segment as a whole, it is important for the micro and pub-brewing industry to emulate their larger brethren in the development of quality control and assurance programs.

The definition of sterility must be clarified before any discussion of quality control. Sterility means absolute freedom from microorganisms. Sterility is not possible in a brewery, since trace amounts of microorganisms are present at all times. It is the brewer's duty to ensure that these microorganisms do not multiply. If there is an increase in micro-organism activity, then a typical infection occurs. (In Fig. 1 the growth curve of micro-organisms according to Hinshelwood is presented.)

In the lag-phase, there is an adapation of the organisms to the new environment, followed by exponentional (logarithmic) growth under optimal conditions. Then, through shortage of nutrients and accumulation of inhibitory metabolic products, the stationary phase (stagnation of cell growth) is reached. This leads to the decay phase.

Beer spoilage

The growth of micro-organisms in beer will lead to damaging changes to the properties of beer. Micro-organism development can occur at each step of the production process, and later in the packaged product.

The micro-biological control stages at Frankenmuth Brewery, Inc. are illustrated in Fig. 2. If there are beer spoilage micro-organisms detected by any of the control steps, then measures have to be taken depending on the degree of infection already developed. If there is only a trace of infection, practically no metabolic products will occur, and the beer will not be damaged. In this case, a sterilizing filtration can help. A flash pasteurization or tunnel pasteurizer are possible alternatives. This heat treatment is not safe at all times, because the killing effects depend on the number of cells present. The most effective (and the most expensive) method is through sterile filtration and flash pasteurization. As an example, if the beer is already damaged in the aging stage, and the brewer still wishes to package the beer (Not a sensible course), it would be necessary to remove the metabolic products of the micro-organisms. This can be done by the use of active carbon in filtration. Nonetheless, micro-organisms can be forced through by pressure surges and still damage the packaged beer with their metabolic products.

Measure of protection

A measure of protection from infection is provided by the composition and properties of beer. This protection is never complete, but the danger of infection is decreased. In Fig. 3 the primary conditions for successful protection from damaging micro-organisms are listed.

The most important points in a micro-biological survey of a brewery are shown in Fig. 2. All samples are membrane filtered and incubated on nutrient media at 27-28 degrees Celsius for the detection of beer spoilage bacteria (anaerobe) and yeasts (aerobe). Turbid samples are examined either by plating out the deposit or through direct addition of nutrient agar. Yeast samples are directly plated out or added to liquid medium. In the following figure (fig.4) we see the most used media's in biological quality control.

No perfect medium

There is still no perfect medium for the detection of the total flora of fermenting wort, beer or brewing ingredients. Also not existing is a single medium for isolation of specific groups of yeast or bacteria of our interest. Always remember the infecting organisms which are present have to grow on the medium used.

In summary, growth of unwanted micro-organisms in beer causes visible, sensory and physico-chemical changes. The amount of organisms determines the length of time before a detectable infection appears. Spoilage bacteria can damage beer (1) directly in the bottle or (2) indirectly in the production process, for example through the release of metabolic products.

All mentioned media's are available from the Siebel Institute in Chicago, IL. Their technical service is very helpful in answering any questions that brewers might have, and they offer frequent technical courses as well.

Another avenue for microbrewers is through the established brewers organizations. The Master Brewers Association of the Americas (MBAA) and the American Society of Brewing Chemists are excellent resources. MBAA offers regular courses in brewing technology. [Figures 1 to 4 Omitted]

Fred M. Scheer is the Master Brewer and Technical Director at the Frankenmuth Brewery, Inc., Frankenmuth, Michigan. He is an active member of the MBAA, ASBC and DOEMENS, the German Master Brewers Association.
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Title Annotation:1990 Microbrewery Report
Author:Scheer, Fred M.
Publication:Modern Brewery Age
Date:May 14, 1990
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