I currently have a Young's Double Chocolate Stout clone (extract & specialty grains) in the primary. I got the recipe from one of the responses to this forum question. (You have to be logged in to beeradvocate to see the responses.)

It's been fermenting for 11 days. Since about day 6 when airlock activity slowed dramatically, there has been a gooey yellow-white film on top of the beer that is holding some bubbles trapped underneath. This film doesn't look like any infections I've ever seen pictures of; it's not fuzzy or crackled and there are no radial patterns laying on top. I don't think it's infected, but I've never seen anything like this in the dozens of batches I've ever made. I think it may be yeast and/or lactose trapped on top of maybe some protein film.

This is the first time I've used lactose (12 ounces of it), cane sugar (4 oz), invert sugar (8 oz), and yeast nutrient (1/8 tsp). If you have experience with any of these ingredients, have you noticed interesting krausen after fermentation slowed similar to what I've described?

2 Answers 2


Answering this question is dependent on knowing the strain of yeast you used.

After fermentation slows sometimes dissolved CO2 can start to carry flocculating yeast to the surface and make weird films of yeast like you describe. It doesn't sound like too big of a concern to me. Furthermore, the addition of lactose (a non-fermentable sugar) could also be increasing the viscosity slightly depending on when you added it.

Beyond that, it sounds fairly normal to me, what you are seeing. If its the first time you have used yeast nutrient as well then its likely that you are just seeing fermentation slowdown in a manner you aren't used to in the past.

  • Thanks for the reply. Good to know about the nutrient causing slowdown to be different. In past batches it seemed to go from full-throttle fermentation to no airlock activity in one day. This time around I noticed it slowed down more slowly to where it's still bubbling once every couple of minutes, even after 11 days.
    – JackSmith
    Commented Jan 11, 2010 at 15:23
  • Sorry - I used WLP002 - English Ale Yeast. The recipe calls for WYeast 1318 London Ale Yeast III. My LHBS doesn't carry WYeast and several conversion charts I found online say that WLP002 is a good analog. WLP002 is supposedly highly flocculant.
    – JackSmith
    Commented Jan 11, 2010 at 15:26

There's a fair amount of actual chocolate in that recipe. That layer that you're seeing may actually be cocoa butter.

It might be terrifying, but: smell it taste it. That'll give you a great idea of what it is.

  • Oh, yeah! I forgot about all the cocoa butter. The layer is a sort-of buttercream color, just like cocoa butter. When it was actively fermenting, the krausen had a good bit of dark cocoa powder floating on top of it. I tasted the wort just before pitching the yeast and it was gritty with cocoa. Gritty and delicious. :D
    – JackSmith
    Commented Jan 11, 2010 at 15:32

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