Check the listing for details. Yeast Extract Agar Dehydrated. Condition: Brand New. Listed at 11.87 USD. Yeast Extract Agar Water can contain a large number of microorganisms, particularly coming from the earth and vegetation. Yeast Extract Agar is formulated according to the formula described by Windle Taylor for the plate count of microorganisms in water. Yeast extract and peptic digest of animal tissue provide nitrogenous compounds, vitamin B complex and other growth nutrients. From the water sample, make a decimal dilution bank with Ringer Solution and take aliquots to 2 parallel series of plates. Pour the molten, cooled (45°C) Yeast Extract Agar and homogenize with sample. Incubate one of the series of plates at 35°C for 24 hours and the other series of plates at 20-22°C for 3 days. Separate counts are made of the organisms forming visible colonies after 24 hours at 35°C and the organisms forming colonies after 3 days at 20-22°C. Select the plates containing 30-300 colonies.