I'm doing a series of smash beers all using the same yeast same temp same grain. I'm noticing a big variation in flocculation on the current batch (forgot the Irish moss oops) WLP001 by the way. Im assuming I'm going to get a bunch of "DUH" comments but I have always used the Irish moss to coagulate the trub in the kettle for clarity never thinking of it going on to the ferment and conditioning, anybody know?

1 Answer 1


Ideally when using irish moss, very little of it should end up in the fermentor. It's a good idea to let the boil settle for 10-15 minutes after flameout so that the moss and the proteins it's attracted have time to fall to the bottom of the kettle.

But even if it does make it to the fermentor, it won't have any significant affect on the yeast:

  • The irish moss will sink pretty quickly to the bottom of the fermentor, and won't affect the yeast in suspension.

  • Irish moss works in the kettle by electrostaticly attracting oppositely charged particles, in particular proteins, that are in the wort forming larger molecules that sink rapidly. Irish moss is negatively charged, and the proteins are positively charged, so they attract. Yeast are negatively charged, so there is no attraction - instead a slight repulsion, although this will have no practical affect.

So, Irish moss has no affect on yeast flocculation. If you were to use a different fining that is positively charged, such as Polyclar, then this would cause the yeast to flocculate and sediment quicker.

Can you be sure it's yeast in suspension you're seeing and not protein haze?


  • I'm getting a collection of pretty dusty white material on the sides of my carboy which I have always assumed was yeast but could be protine haze I guess
    – Ryan Shdo
    Mar 6, 2013 at 21:15
  • 1
    you could post a photo and a new question to ask what the white stuff in your carboy is. It could be anything from protein, yeast, pellicle from contaminating organisms or actual dust!
    – mdma
    Mar 6, 2013 at 21:36

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