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

 

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