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Frank Reitz
09/29/08 04:07 PM  
Top/Bottom fermented
Hi all

This simple question should have only one real answer although I've seen so many different answers.

In the beginning of my brewing career I knew I didn't know. Then I read about it and brewed some beer and then I knew. Now I am unsure again and before I pass on my knowledge about this I want to be sure which is true:

The difference between bottom fermented and top fermented beer refers to

1. the temperature range in which the beer has been fermented

2. in top fermented beers the yeast will rise to the top of the beer - in bottom fermented beers it will drop to the bottom.

3. both 1 AND 2

4. something completely different

The reason why I have doubts is that professional brewery sites state #2 is the correct answer. My own take is #1 since the bottom fermented pilsner I made once had a layer of yeast on top during fermentation (cause of the co2 release) and it all dropped to the bottom at the end of fermentation. Exactly as my top fermented ales.

I am asking you for valid solid proven true information - not what you think you know. Anyone?

Thanks

tankdeer
09/29/08 05:47 PM  
Re: Top/Bottom fermented
Both 1 and 2 really. Although lager yeasts CAN ferment at ale temps, the flavor is usually not as good. However Ale yeasts generally CANNOT ferment at lager yeast temps. In addition, lager yeast can eat different polysaccharides that ale yeast cannot; maltotriose specifically. To my knowledge Saccharomyces C. can only eat disaccharides
Frank Reitz
09/30/08 12:57 AM  
Re: Top/Bottom fermented
Thanks tankdeer.

If #2 holds true then the following confuses me:

To my belief both bottom fermenting yeasts and top fermenting yeasts behave the same. During fermentation they rise to the top. After fermentation they drop out.

All yeasts work from within the wort, not from the top of the wort or the bottom of the wort.

True or false?

Thanks

MarkO
09/30/08 02:29 AM  
Re: Top/Bottom fermented
I think the distinction is fairly simple:

top-fermenting yeast species have a hydrophobic surface, and glom onto CO2 bubbles, so they float to the top;

bottom-fermenting species do not do this to the same extent.

I don't think either term is particularly descriptive, as one can find plenty of "top-fermenting" yeast in the bottom of a fermentation environment. It is very descriptive of observation with the naked eye, however: everyone must have seen the pockets of ale yeast floating to the top of fermenter with a CO2 bubble, only to be released as the bubble pops.

I would swear to the fact that all yeasts work within the wort, as you have suggested, rather than on top or a the bottom. I think the floaty stuff on some of the wild yeast fermentations is really just a byproduct of yeast activity rather than yeast itself.

But caution: I ain't no micromycologist.

petec
09/30/08 07:14 PM  
Re: Top/Bottom fermented
Besides temperature preferences for fermentation and the maltotriose side of thing for differences ..........

I think the distinction is based heavily on historically thick top cropping english ale yeast (ie. compared against german lager yeasts which were most likely not topcropped for successive generations). NOt that all yeasts don't have some riding on the surface, but that ale yeasts had a particularely thick blanket of yeast riding up there.

having never really watched many lager fermentations, is the rate of CO2 production enough to keep a thick head of yeast on the top surface for any length of time?

petec

Frank Reitz
10/02/08 04:19 PM  
Re: Top/Bottom fermented
Petec, yes you're absolutely right. I have also contacted both whitelabs and wyeast about this matter and I have responses from both.

They both agree that it relates to the temperature AND how vigorous the fermentation is. Some lager yeasts creates a strong fermentation and rises to the top as an ale yeast would and vice verca according to one of the companies.

Also, MarkO's hydrophobic surface theory makes sence and might also be a factor.

Thanks all

/Frank

 
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