Universal Beer Agar (UBA)

The medium isolates bacteria and yeasts, capable of growing under brewing conditions, which are of real significance for the brewer such as wort spoiling bacteria, common environmental bacteria (coliforms), and beer spoilers that require oxygen.

Yeast extract is a source of vitamins, particularly of the B-group. Peptonized milk contains lactose as an energy source. Tomato juice is a source of carbon, protein and nutrients. Dextrose is a fermentable carbohydrate providing carbon and energy. Potassium phosphates act as a buffer system. Magnesium sulfate, ferrous sulfate and manganese sulfate are sources of ions that stimulate metabolism. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent. The incorporation of beer in the medium adds hop constituents and alcohol which eliminate many airborne contaminants not originating from pitching yeasts or beer, and therefore minimize false positive results. Also, it stimulates the growth of beer spoilage organisms, such as lactobacilli, pediococci, Acetobacter, and Zymomonas spp.

For the detection of bacterial contaminants in pitching yeasts, cycloheximide (1 mg/L) may be added.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 55 grams of the medium in 750 mL of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Add 250 mL of beer without degassing when the medium is still hot. Mix with agitation. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 10 minutes. Cool to 45-50 °C, mix well and dispense into plates.

Instructions for use

• Incubate at 28-30 °C and observe after 3 days.
• Incubate aerobically to detect Acetobacter.
• Incubate anaerobically to detect Lactobacillus, pediococci and Zymomonas.

• Kozulis, J.A. and Page, H.E. A new universal beer agar medium for the enumeration of wort and beer microorganisms. Proc. Am. Brew. Chem. 52-58 (1968).