BIAB, Trub and Fermentation

I brewed two consecutive BIAB beers and pitched off the same yeast cake (lager yeasts) for both. I was looking at the carboy the other day and noticed multiple layers of tan colored trub in the bottom with thin layers of white trub in-between. It is my understanding that this white layer is yeast.

This made me wonder whether BIAB is a method that may lend itself to stuck fermentation. Specifically, given the amount of particulate matter dropping out of suspension I wonder if this can either:

1. Drop yeast out of suspension
2. Coat yeast at the bottom of the carboy in such a way as to impede their ability to access sugar

I have not had a stuck fermentation yet with BIAB but I noticed by searching that others on this board have. Just a thought, I am new to brewing so I would be happy to hear whether either of these thoughts are valid or not and why. Thanks.

I nevr had problems with my BIAB lagers. I must have done 5-6 of them this year, fermenting Oktoberfest as we speak

I have heard that excessive trub is a result of BIAB method. Are you asking if this buries the yeast to the point where pitching on a yeast cake will not give enough access of the yeast to the new wort? Would removing and quickly washing the yeast to separate the trub matter prevent this?

tennesseean_87 said:

I have heard that excessive trub is a result of BIAB method. Are you asking if this buries the yeast to the point where pitching on a yeast cake will not give enough access of the yeast to the new wort? Would removing and quickly washing the yeast to separate the trub matter prevent this?

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Yes, that was basically my question. I am hesitant to go through washing as I was under the impression that when repitching on the same cake we should do that as soon as possible and avoid too much exposure to oxygen.

in general unless the next beer is significantly bigger, you shouldn't be pitching directly onto a full cake. its not beneficial and you're over-pitching. i'd wash the yeast first.
https://www.homebrewtalk.com/f163/yeast-washing-illustrated-41768/

tennesseean_87 said:

I have heard that excessive trub is a result of BIAB method.

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not sure where you heard that, but IME that hasn't been the case and doesnt make any sense to me.

In DeathBrewer's BIAB stovetop thread a few people mentioned it. They said it was due to not using the grain-bed as a filter because you just pull the bag out instead of running the water out of the bottom. I've not done it before, but am hoping to try it.

tennesseean_87 said:

In DeathBrewer's BIAB stovetop thread a few people mentioned it. They said it was due to not using the grain-bed as a filter because you just pull the bag out instead of running the water out of the bottom. I've not done it before, but am hoping to try it.

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that would result in grain particles entering the BK pre boil - wouldn't have any effect on the break material after the boil

I use the same paint strainer bag for BIAb and to filter after the boil - i haven't noticed any negative side effects for poor yeast performance or off flavors

in fact some break material is beneficial for healthy fermentation

I don't see how this could impede the yeast. For one the trub will fall out first when everything get's stirred up. If you decide to pitch on a cake, just swirl up the fermenter. The yeast will become suspended in the wort and the other crap will fall out. It is overpitching though and only worth it if you are making a massive beer.

There's no issue with washing yeast. You can get several batches out of a single yeast cake.

terrapinj said:

that would result in grain particles entering the BK pre boil - wouldn't have any effect on the break material after the boil

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+1

tennesseean_87 said:

They said it was due to not using the grain-bed as a filter because you just pull the bag out instead of running the water out of the bottom.

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I actually run the water out of the bottom of mine so I guess I wouldn't notice that anyway.

I've done 4 BIAB batches now and have had great attenuation every time. I did pitch onto 1/3 of a cake of Patersbier for my 1.080 Carmelite Tripel. The other 2/3 I removed and washed to save for a Dubbel later this year. With the Tripel I had active fermentation in 2 hours and it blew the airlock about 12 hours later (with plenty of Fermcap-S foam control). So I don't think there are any worries of the trub hiding the yeast.

I have noticed a pretty good amount of trub with BIAB, but I've never done a traditional AG brew to compare to. I don't' the trub affects anything at all, so I don't worry about it. It gets left behind when I rack out of primary.

maltoftheearth said:

I have not had a stuck fermentation yet with BIAB but I noticed by searching that others on this board have. Just a thought, I am new to brewing so I would be happy to hear whether either of these thoughts are valid or not and why. Thanks.

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Stalled fermentation can be caused by many things such as yeast health, pitch rate, mash temperature, etc. Can you provide some links that show a correlation between stuck fermentations and BIAB?

When it comes to "pitching on a yeast cake" I'd be more concerned about not washing the yeast and massively over-pitching. This thread may be useful to you.

https://www.homebrewtalk.com/f163/why-not-pitch-your-yeast-cake-166221/

If you still want to rack new wort onto an old yeast cake then you can either swirl the fermentor as you transfer the wort or gently stir the sediment on the bottom after transferring.