Soapy Flavours (yeast)

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Pat Casey

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Something has come up with a customer's beer. I wondering whether anybody who heavily aerates their starters, ie stirplate or pure oxygen, has ever had any (occasional) problems with soapy tastes in their beer.

I've used a DIY stir-plate for every yeast starter for every beer I've made in the last few years and never noticed a soapy taste - I'm not sure how the two could be related either.
Collecting data to test a hypothesis. Wolfy, never felt you've left a starter too long on the stirplate?

Had a customer who had a run of soapy beers.
The traditional culprit is the breakdown of yeast; if the beer is left on the yeast cake too long, as cells breakdown they release lipids that combine to make soap (effectively).
That wasnt the answer in this case. Turned out to be Chlorine; caused by soaking his equipment in Chlorinated (read Bleach) sanitiser too long and/or strong.
The Cl was penetrating the plastic, then leaching back into the beer and making some nasty compounds. Some Chlorophenols are detectable in the parts per billion range; my personal hunch is that the soapy flavour its a reaction between lipids, fatty acids or glycerols and Chlorine.
The same flavour has come up occasionally, after first addressing the time the beer spends in the fermenter, appropriate adjustments to the cleaning and sterilising regime usually solves the problem, personally I favour Sodium Percarbonate as my general purpose cleaner/steriliser.
Tho its quite possible that if a lot of dead yeast is going into the fermenter from a mismanaged starter that yeast could be the culprit.
Collecting data to test a hypothesis. Wolfy, never felt you've left a starter too long on the stirplate?
The longest I generally leave each step of the starter-process on the stir-plate is 48hours (usually it's just 24h), and as I suggested have never noticed a problem.
However, I also let the yeast settle, decant the spent starter and pitch only the yeast, and use stepped-starters (which would minimise the presence of dead yeast) both of which may or may not be the same procedures that others use.
No chlorine is involved, nor is long term autolysis as the customer has detected soapy flavours in some beers within 10 days.

Soapy flavours are associated with fatty acids, capric acid in particular. The customer uses straight oxygen for his starters and on pitching. Normally the lipid content of yeast cells is about 2-5%, however de Clerk states "The lipid content of old yeast cultures, or yeast grown under conditions of strong aeration, may be as high as 10-20%." ( A Textbook of Brewing, Vol 1, p367).

I think this is the root cause of the problem, but am curious as to others' experiences, especially with straight oxygen.

Thanks for your replies Wolfy and Mark.

My first-ever batch had a bad soapy taste/mouthfeel. My main problem (despite thinking I needed to ferment at 25C) was that I racked to a secondary by opening the tap and letting the beer drop the entire height of the fermentor to the bottom.
Could the problem be over oxidation? beyond the normal cardboardy flavours associated with oxidation.

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