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To add yeast or not to yeast ?

Hey all,
Just wondering how many people use yeast to cover their cultures before they add flies to try to reduce bacteria growth. I've been doing it, but sometimes it seems like it causes this nasty yellow coating over the top of the media. It doesnt seem to affect production, but I don't know, just looks wierd. Let me know!

I also add yeast - only 4-5 small pellets, pieces or what you want to call them. I dont get the yellow and I have no bacteria. I got yellow once but I added way too much yeast.

I usually make my mixture in the container, add water and mix in the container. I add a few sprinkles of active yeast into some warm water. Mix it, then add a tablespoon to the top of the mixture. I keep the open active yeast in the fridge (for months at a shot). When the mixture sets, there isn't any air pockets. Doing it this way I found I do not even need a mold inhibitor. I haven't had one bad batch yet. Since there are not any air pockets on the bottom etc, and the yeast takes over the top,, no mold issues whatsoever. I always add some cheap cool-aid mixture for coloring in the dry mixture which also is the sugar (Hmmm,, do not use sugar free!!) that the active yeast feed off of. --Corey

I've been following the Black Jungle directions and mixing 1/4 tsp into a cup of hot water, then adding about a tablespoon to the culture, and i get the weird air pockets and yellow nastiness. I just don't get it.

I make a mix of:

8 pts potato flake
2 pts powdered sugar
1 part brewer's yeast
Some grains of baker's yeast

I mix the dry stuff. I put about an inch and a quarter of the mix in a 32oz fly container. mix in 50/50 white vinegar and water until I think the consistency is good. Let it set for a minute or two to firm up. Then I sprinkle a bout ten-twenty -thirty grains of baker's yeast on top of that. Add flies and wait for maggots. Excelsior is added as soon as I see maggots.


Darts with parasites are analogous to mixed tanks, there are no known benefits to the frogs with either.

If tone is more important to you than content, you are at the wrong place.

My new email address is: and new phone number is 773 577 3476

I do pretty much the same thing as Rich.

8c Potato Flakes
1c powdered sugar
2 tsb methyl paraben
1/2c Brewers yeast

I then put about 1/4 tsp of bakers yeast and some powdered sugar into some warm water and mix. When the yeast starts producing bubbles and a foam on the surface, the yeast has been activated, and you can use a dropper to cover each culture with this.


Just out of curiosity why do you wait to add the Excelsior?

The addition of sugar after one uses baker's yeast is not needed. That is if you are using any type of instant medium. See the reason the yeast is added to the medium is once the yeast touches the medium (usually a sugar/starch combo) it starts to produce a sugar alcohol and this is what the flies actually eat. I have never heard of this as a mold inhibitor. I have never had mold in my cultures even once. You could try using the Carolina Biological supply anti fungal blue medium. I have used this with great success. And it only cost $ 12 for a pretty big bag.


The blue Carolina medium is not anti fungal, it`s only a blue dye so you can see the larvae in the medium. The maggots actually eat the yeast being produced or it would be useless to add any inactive, nutritional yeast to the mix. It wouldn't serve any purpose. your actually culturing a beer paste and converting all the starch and sugar to yeast for the larvae and flies to feed off of. you add the nutritional yeast as a starter till the active yeast kicks in and starts fermenting the mixture. With high amounts of corn sugar you get a vinegar produced which in turn retards mold growth. Spray malt smells better though if you add hi amounts of flies and the cultures aren't meant to last as long. This is why cultures made w/ beer slurry work so well. You have a mix of active and inactive yeast ready to bloom once the alcohol level is reduced by mixing w/ more sugar and carbs. It's like throwing a bunch of cattle in a low cut field. They may starve to death before the grass grows but if you throw in some hay and leave time for the grass to grow the heard produces. A slurry culture is to fruit flies as a full field of tall grass fertilized and growing is to a heard of cattle.

ha, herd of cattle, ya ive heard of them.

oh, not to say that there isnt tegosept or methyl parabyn(sp?) something added to all carolina or wards mixes, blue or white. i believe they all have anti fungal/bacteria chemicals added.

Thank you for your question.

This appears on page 232 of our 2006 Science and Math Catalog.
The coloring agent appears to be Copper Sulfate ( this is a proprietary compound , so I don't have exact
formulation information).

Sam Beckom
Product Information

Karen Parker/Carolina
02/14/2006 07:25 AM

I asked Carolina's customer service what the blue appearance was in their mixture.
Copper sulfate is a fungicide used to control bacterial and fungal diseases of fruit, vegetable, nut and field crops.
I used Carolina's mixture for several years with success. until i discovered ED'S fly meat.

WARDS Instant Drosophila Medium

Improved Formula for Higher Yields

This ready-to-use formula, developed by WARDS, just needs water. No cooking, sterilization, or additional inhibitors are necessary to create the perfect environment for culturing Drosophila. In addition, the medium won't soften or liquefy, so flies won't drown. Choose white or blue for better observation of developing larvae. The color won't harm your Drosophila. One liter is sufficient for approximately 60 standard cultures.

if the blue is copper sulfate it`s not added as a fungicide, only to better view larvae for experiments. I can't get thru to them (lunchtime) but I've asked before and been told its only a dye. I used to have to order blue when they were out of white and was worried about the effects.

Well if one company is adding blue dye then its for better maggot viewing. If another company is adding copper sulfate that turns the mixture blue, its for mold inhibiting. Plain and simple. Aren't Carolina Supply and WARDS different companies?

it's all just blue dye.The help desk doesnt know anything, talk straight to the lab. it`s probably not copper sulfate unless copper sulfate is a food grade food coloring.

KarenH Wrote:Just out of curiosity why do you wait to add the Excelsior?

Hmmmm....this is interesting. Anyone else 'wait' until adding excelsior?

"Time flies like an arrow, fruit flies like a banana".

Nope... and with home made media I nuke the cultures for 30 seconds each.


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