help with food

David Ish-Horowicz d_horowicz at
Mon May 22 08:05:16 EST 1995

In article <3ppnjl$3es at>, flh at
(Frances Hannan (Zoology)) wrote:

> delidakis at writes:
> >if you have any modifications on the following recipe, we'd like to try them:
> >Per 3 litres of water we use:
> >70 g  sugar (sucrose)
> >170 g  yeast (baker's yeast cake previously autoclaved to make sure it's
> >       dead)
> >30 g  agar
> >200 g  cornflour
> >+ 50 ml of 10% Nipagin (0.17% final)
> You could try adding a mixture of propionic and phosphoric acids to the 
> fly food after it has cooled down a bit (if food is too hot you will 
> still get some bacteria/slime). Try 0.5% propionic acid and 0.05% phosphoric 
> acid (final concentrations). Good luck

Although switching mould inhibitors can be a good way of losing
contaminating bacteria (we too use the acid mix), take care NOT to use
BOTH nipagin and proprionic/phosphoric acid inhibitors together. That
prevents live yeast growing at all. 

Also, the active mould inhibitor is free proprionic acid. The phosphoric
acid serves to reduce the pH to 4.0 so the proprionic acid is unionised;
the amount of the former one needs to use will depend on the food recipe
and ingredients and maybe should be roughly titrated the first time

David Ish-Horowicz

David Ish-Horowicz
ICRF Developmental Biology Unit, Oxford
d_horowicz at

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