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Foam stability

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I wonder how the commercial belgian breweries can get good foamstability even though they leave the beer on long secondary fermentations in cold degrees 4-8 weeks.
I have some theories, but I dont know if they are entirely correct.
1. They add Propylene glycol alginate
2. They add isomerised hop extract before bottling
3. They add a little nitrogen in the beer

As far as I know a long lager-time (I think you mean lager time and not the time of the secondary fermentation) doesn't negatively affect the foamability. What information that I am missing tells you it does?

Yes I mean lager time. When the beer matures in cold storage tank. The purpose of this should probably be to get rid of old yeast and get the beer clearer from rests of hops and malts. The latter should probably have negative effects on the foamstability.
I have myself problem with foamstability in my beer with long storagetime in both warmer and colder degrees.

The problem that you are referring isn't directly a bad foam stability. The problem which you are referring to is the lack of carbon pressure, because there aren't enough healthy yeast cells in the beer to have a proper re-fermentation process in the bottle. To fix this issue, they seed fresh yeast (the same yeast as used before or specialized bottle yeast) with the bottle-sugar. This yeast converts the new sugar to ethanol and CO2 (and of course some other stuff like esters). This newly formed CO2 isn't able to leave the beer, because the beer has a cap on. This leads to an increase in carbon pressure and therefore to an increase in foam-ability.

Sorry if I'm not clear enough.
I know very well that they add new yeast and sugar after coldstorage.
But when the beer is in storage, malt proteins and hoprests drop to the bottom. Malt proteins and hoprests are good for foamstability.


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