I need to add yeast to cut bananas to make food for my Drosophila fruit flies. Currently, what I do is combine 1/2 teaspoon calcium propionate, 3 teaspoons cream of tartar, 2 tablespoons water, and 1 teaspoon yeast in a jar, give it a good shaking, and set it aside while cutting up the bananas. After the bananas are cut up into tiny cubes, I give the jar another good shaking, then pour over the bananas and mix by hand for about 30 seconds. During this mixing, it seems like a lot of liquid comes out of the bananas. Then, I spoon it into the cups where the flies will live.
Until recently, I used a whole package of yeast,
which is about 2 teaspoons. I've been battling
problems with bacterial overgrowth, and cutting
the yeast back to about half has helped a lot.
I tried lower amounts, but that seemed to hurt
the production of flies.
Giving the jar two good shakings seems to have
helped. My theory is that the first shaking
mixes the ingrediants and wets the granules of
active dry yeast. The time delay while I cut up
the bananas allows the water to soak into the
granules. Then, the second shaking breaks up
the now softened granules and distributes the
yeast more thoroughly.
There does seem to be some yeast activity which
starts in the jar, even though I've added no
sugar or starch. The first food the yeast get
should be the liquid from the bananas.
I'm still not satisfied with my results. If
I use the whole package of yeast, I lose more
cups to bacterial overgrowth, but the best cups
produce more flies. If I use half the amount,
it seems like the best cups produce less, but
I get fewer bad cups.
I'm thinking that maybe I'm not handling the
yeast right before adding it to the bananas.
Maybe I should add sugar or flour to the yeast
at the jar stage, so they'd get started eating
earlier. The cream of tartar is a buffered acid
which helps to suppress bacterial overgrowth.
Calcium propionate is a mold inhibitor which
also helps to suppress bacteria. The water is
always room temperature bottled water, not tap
Any of you yeast-proofing experts out there have
- posted 6 years ago