Current Bloomington Recipe for Drosophila Medium

This is our modification of a recipe used by John Loera at the University of Texas at Austin. The Texas recipe is apparently based on the malt medium described by Lakovaara (1969), with the addition of soy. This is a firm medium that resists liquification from heavy larval activity and stores well at 10^o -- 14^o C. It will keep for at least a month if tightly plugged, although weaker stocks will do better on food less than a week old. If stored at 4^o C you may find that it 'weeps' when brought to room temperature. Leaving fresh flats at room temperature for 24 hours before moving them to 4^o will reduce weeping.

The recipe
This makes about 42.5 liters of food, enough to fill about 4,250 vials with 10 ml of food each. Even when hot the food is thick - be sure your pump can handle it before you make a large batch.

Cooking instructions

Bad food is often simply dry food. Seemly small changes in the cooking process can make a significant difference in the quality of the food if those changes result in increased water loss. If you cook small batches in a large kettle, don't have a covered kettle, need to cook the food longer, or are in a particularly dry environment you might need to increase the proportion of water in this recipe.

1. Measure malt and corn syrup (separately), set aside.
2. Mix yeast and soy flour, hydrate with 3 liters of the water, more if necessary (use a hand mixer, or press out larger lumps with fingers or the back of a large spoon), set aside.
3. Measure cornmeal and agar into a large container, add 5 liters of the water, mix until lump-free, using more water if necessary to produce a smooth slurry.
4. Set aside about 4 liters of the water.
5. Bring the remaining water to a full boil.
6. Stir cornmeal and agar mixture again (add some of the set-aside water if needed) and pour the smooth slurry into the rapidly boiling water (both points are important to avoid lumps that will clog the pump). Stir the pot at the same time if possible (we have an electric stirrer). If the cornmeal-agar mixture begins to form lumps as it is poured, add more of the set-aside water and mix well before pouring the rest of it into the boiling mixture. Use any remaining set-aside water to rinse the cornmeal-agar dregs into the pot.
7. Stir in malt. Lumps will form at first, but unlike cornmeal lumps, these will cook out.
8. Stir in malt-soy mixture and then the corn syrup.
9. When mixture has just begun to bubble at the edges start timing and cook for 10 minutes, stirring frequently.
10. Turn off heat source.
11. Stir in propionic acid. If you have time, cool to 70^oC before adding the acid (we don't).
12. Dispense the medium.
13. Cool before plugging if time allows.

Ingredients notes

Cornmeal

Not all brands of cornmeal are comparable - test before you buy in bulk. We use Quaker® yellow cornmeal (~$10 per 25 lb. bag through our campus food services).

Soy flour

Soy flour is available from ADM, Protein Specialties Division, Decatur, IL 62525, phone 800-637-5855, fax 217-362-3959, as Nutrisoy® (product #063-100, ~$30 per 50 lb. bag).

Agar

The amount of agar should be determined empirically for your brand of agar. We buy 100 lb. barrels (~$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).

Yeast

We use SafPro Relax+YF deactivated dry yeast from Lesaffre Yeast Corp., phone 877-677-7000 (product #73050, ~$76 per 50 lb. bag).

Malt

Buy malt from a brewing-supply house -- scientific grade is far too expensive. We buy plain light dehydrated malt from L.D. Carlson Co., 463 Portage Blvd., Kent, OH 44240, phone 800-321-0315, fax 800-848-5062 (~$77 per 55 lb. box).