Hard Agar Medium for Egg Collection Plates
Updated March 30, 2007
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This is a firm medium that keeps well and makes a good base for egg collecting. Wrap filled petri dishes and store at 4 -- 14oC (they should keep for at least 6 weeks). Substitute molasses for the corn syrup if you prefer a dark medium, or add food coloring. This recipe makes about 60 6 x 2 cm plates.
The recipe
Water 2.25 liters
Agar 88 grams
Light corn syrup 350 milliliters
10% p-Hydroxy-benzoic acid methyl ester in 95% ethanol 38 milliliters
Cooking instructions
  1. Mix water, agar and syrup.
  2. Boil until agar is dissolved.
  3. Cool for 5 minutes or more, stir in p-Hydroxy-benzoic acid methyl ester.
  4. Dispense into petri dishes.

Ingredients notes
The amount of agar should be determined empirically for your brand and lot of agar. We buy 100 lb. barrels of "Agar 700" (product #40004, ~$1,295) from Moorhead & Co., Inc., 6923 Woodley Ave., Van Nuys, CA 91406, phone 800-423-3170, fax 818-787-2010.
Corn Syrup
We use Karo® light corn syrup (about $8.40 per gallon through our campus food services).