Culture Method for Quality Control of Beer

By: Jvo Siegrist, Microbiology Focus Edition 1.4

Product Manager Microbiology…. ivo.siegrist@sial.com

The classical cultural method for the quality control of beer is still important. Most modern use at least a pre-enrichment step and the costs for the analysis are lower.

Traditional methods are based morphology, staining methods, enzyme reactions (metabolism) and diverse media. One of the first steps is the filtration of the beer followed by an incubation of the filter on an agar plate. Suspect colonies are then examined under the microscope followed by staining procedures and biochemical tests. More details of a systematic identification can be seen in Figure 1.

Figure 1: Identification flow chart for beer spoilage bacteria
* obligate beer spoilage. ^ potential beer spoilage. ° indirect beer spoilage. Numbers in % gives the frequency of spoilage organisms from quality complaints for beer (1980-2002) (Source: Handbook of filling techniques: Grundlagen und Praxis für das Abfüllen flüssiger Produkte; S. Blüml, S. Fischer 2004)

Listed in Table 1 are the typical media used for the detection of spoilage organisms like lactobacilli, pediococci, Pectinatus, Megasphaera molds and wild yeasts in the brewery and fermentation industry. Only a few genera of bacteria, wild yeasts, and molds cause spoilage of beer and wine because of the alcohol content, low pH, and other ingredients having inhibitory effects. Some of these contaminants can interfere with fermentation or have deleterious effects on flavor and shelf life. Most of these spoilage organisms make the beer acidic or producing substances with a bad taste like diacethyl and tetraden compounds. Pectinatus and Megasphaera are also dangerous pathogens.
 

Medium   Cat #
CaCO3 Agar   40545
Corn Meal Agar   42347
HiCrome™ OGYE Agar Base   66481
Lysine Medium   L5910
Malt Agar   M9802
Malt Extract Agar, modified   97218
MRS Agar   69964
MRS Agar, original acc. DeMan-Rogosa-Sharpe   30912
MRS Agar, Vegitone   41782
MRS Broth   69966
MRS Broth modified, Vegitone   38944
NBB Agar   64198
OGY Agar   75310
Plate Count Agar   70152
Plate Count Agar according to Buchbinder et al.   88588
Plate Count Agar, Vegitone   19718
Plate Count MUG Agar   51413
Raka Ray Agar, Base   02538
Rogosa SL Agar   R1148
Rose Bengal Chloramphenicol Agar   17211
Schwarz Differential Agar   40608
Tomato Juice Agar   17216
Universal Beer Agar   17226
WL Differential Agar   17215
WL Nutrient Agar   17222
WL Nutrient Broth   W2261
Wort Agar   70196
Yeast Carbon Base   Y3627
Yeast Malt Agar   Y3127
Yeast Nitrogen Base   51483
Yeast Nitrogen Base without Amino Acid   Y0626
Yeast Nitrogen Base without Amino Acid and Ammonium Sulfate   Y1251

 

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