Wort Agar

It is particularly recommended for the cultivation and enumeration of yeasts in butter, syrups and other materials, especially in the soft drinks industry. The medium duplicates the composition of natural wort and its acidity is optimal for many yeasts whilst inhibiting most bacteria.

Malt extract and peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. The medium is suitable for yeasts and molds as it contains a high concentration of maltose and other carbohydrates as energy sources. Dextrin is a carbon source. Dipotassium phosphate is the buffer. Bacteriological agar is the solidifying agent. Glycerol reduces the water activity from 0.999 to 0.95, thereby reducing bacterial growth.

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

Preparation

Suspend 48.25 grams of the medium in one liter of distilled water. Add 2.35 grams (1.9 mL) of glycerol. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 45-50 °C, mix well and dispense into plates. Avoid any unnecessary heating or repeated remelting as this will alter the hydrolysis of the agar, preventing it from setting when cooled.

Instructions for use

1. Prepare the sample and make decimal dilutions.
2. Transfer 1 mL of the suitable dilutions to a Petri dish.
3. Add 15 mL of medium, melted and cooled to 45-50 °C, and mix gently with the inoculum.
4. Incubate the plates at a temperature of 30 °C for 40-48 hours.

• RAPP, M.: Indikatorzusätze zur Keimdifferenzierung auf Würze- und Malzextrakt-Agar - Milchwiss., 29; 341-344 (1974).