Methylene blue test

[lhall]

We've noticed something odd with our yeast. It's a pretty flocculant yeast, and we were advised by one of the big yeast suppliers to add about 5 ml of phosphoric acid to our 1 L dilution of the yeast, to break up the flocs better. When we follow this procedure, we usually get 95% or higher viability. When we omit the acid, our viability drops by 10-20% - that is, more of the yeast cells show a blue stain. Can anyone explain what is going on here?

[kai]

Do you find any difference in total yeast counts when you use phosphoric to deflocc compared to when you don't? We also have a very flocculant yeast and use a small amount of acid CIP detergent to spread them out a little. Without it the yeast clumps like buggery and makes any sort of reliable count impossible.

[Roger Greene]

Hey Linus,

I am not sure what is going on with the acid, but to break up the flocs try adding some EDTA.

[jerrymcmahan]

My guess is that the yeast are beginning to starve and they need the phosphate you're giving them - but it's only a guess. You could try giving them a smidgen of ammonium phosphate and see if you get similar results.