What chemical causes a soapy taste?

You're probably right and could be fermenting your beer too long. Here's an "off-flavour" guide that I've found pretty useful and how to avoid all the unpleasant flavours. It's got your chems in there, too.

http://morebeer.com/themes/morewinepro/mmpdfs/mb/off_flavor.pdf

 

"Keeping beer in the primary fermenter for a long time after fermentation is complete
can cause soapy flavors. After a while, the fatty acids in the trub start to break down
and soap is essentially created." Grabbed that off the morebeer site

 

Soap. The chemical that causes a soapy taste is soap.

 

I've heard of some people perceiving soapy flavors in beers that are heavily hopped with cascade. I did a cascade ahtanum pale ale that had a soapy character that was only in primary for 2 weeks. I also get a slightly soapy character to anchors liberty ale. Perhaps I'm just sensitive to this off flavor.

 

http://beeradvocate.com/community/threads/oktoberfest-ale.125441/

 

But that one isn't wonderfully illustrated.
http://www.howtobrew.com/section4/chapter21-2.html

OP, how long did you leave it in primary? Months?

 

oxidation of fatty acids and yeast cell rupturing.

soap as well if you didn't wash your vessels correctly.

 

“ …yeast cell rupturing.” Ward, do you have an opinion on how long it takes for yeast autolysis to occur on the homebrewing scale?

Cheers!

 

from a podcast on water hardness, if you make a very hoppy beer – say an IPA – and your sulfate levels are not high enough, think not enough gypsum, that can cause a soapy flavor.

And left over soap residue as well.

 

How so? Or if you don't know, what podcast?

 

Basic Brewing radio from.....way back when, i think they interviewed the late Greg Noonan from the Vermont Pub & Brewery, and that was one of the items he brought up. How so, not sure of the chemistry reasons, but think of Burton and their sulfate levels