[oscarvan]

As per my post in "equipment" yesterday I spent a day slaving at a large-ish (10bbl) brewery in Holland. One of the big surprises was that these folks ferment under pressure. It' all goes in a large SS conical fermenter, and the thing is sealed. Dry yeast is re-hydrated in a cornie sized keg, and then forced in with CO2 through a little valve on the side of the thing. Then it ferments....no airlock, no blow off. After a week or so it gets racked to a lagering tank. (They call it lagering, although most of it's ale....the word is used for what we call lagering as well as for what we call conditioning.) The result is a carbonated beer.

Thoughts on fermenting without blowing off CO2?

[morticaixavier]

I've heard of this, but I was under the impression a set level of pressure was maintained, 15psi if I recall.

By the way, good to have you back Oscar.

[jmcamerlengo]

i thought what you thought mort.

I have also heard it produces a unique characteristic to the beer since the yeast are under constant stress and pressure. I'd think the ester level would be significantly higher...

[oscarvan]

By the way, good to have you back Oscar.

Never left, was in the bathroom. Long line.
Seriously, still brewing strong. Just tapped the first dry hopped version of my IPA....it ROCKS.

[tschmidlin]

i thought what you thought mort.

I have also heard it produces a unique characteristic to the beer since the yeast are under constant stress and pressure. I'd think the ester level would be significantly higher...

I believe it is the opposite - the ester level is greatly reduced.

[lornemagill]

ive heard you can ferment at higher temps with no off flavors, no experience or data to back it up though.

[dak0415]

Somewhere, just don't remember, I heard there was a special yeast designed (selected) for fermenting under pressure.

[tschmidlin]

ive heard you can ferment at higher temps with no off flavors, no experience or data to back it up though.

yes, this is what the larger breweries supposedly do - higher temps and gravity then dilute back to "normal" strength.  The higher temps and gravity would lead to increased esters, but it is under pressure so it is reduced.  End result is the "same" flavor profile as if it were open fermented at regular strength in small batches and at lower temps.

[hopfenundmalz]

Somewhere, just don't remember, I heard there was a special yeast designed (selected) for fermenting under pressure.

This stuff.
http://www.whitelabs.com/beer/strains_wlp925.html

Don't try fermenting without a pressure releif valve. You would set it for 15 PSI. Otherwise you could blow up your fermenter. It has happened in production breweries.

Edit - same reason you are required to have a pressure relief on your hot water tank. Anyone see the Mythbuster where they blew one through the roof of the structure built to code? It came down a far way off.

Edit 2 - http://www.probrewer.com/vbulletin/showthread.php?t=23197

[oscarvan]

No dilution going on here.

[tom]

What was the pressure?

[tomsawyer]

I've done several pressurized fermentations, in fact I do all my Brewhemoth batches this way.  Also do small batches in cornies.  Works well, although I must report that my ester levels haven't been noticeably lower.  Maybe the increased temp is offsetting as said earlier.  I ferment at 7psi and then ramp to 15 towards the end.  The Brewhemoth is tested to 100psi.  This is supposed to mimic the higher pressures seen by yeast in large fermentors.

I don't believe they don't have a pressure relief device, theres way too much CO2 produced to hold it all in.  You can get to 30psi quickly.

[kylekohlmorgen]

Some pressure in the fermenting vessel might reduce esters because it keeps the yeast from foaming up above the heat sink (jacket, cooler, etc.). I can't really think of any reason yeast would benefit from additional pressure during fermentation.

Too much pressure is probably a bad thing - not only would there be mechanical yeast stress, but you would hold in a lot of CO2. This creates chemical/osmostic stress on the yeast and its tough to transfer highly carbonated beer.

[tschmidlin]

Some pressure in the fermenting vessel might reduce esters because it keeps the yeast from foaming up above the heat sink (jacket, cooler, etc.). I can't really think of any reason yeast would benefit from additional pressure during fermentation.

Who says the yeast are benefiting?  Increased pressure will activate pathways that affect metabolism.  It seems these pathways reduce esters, but that doesn't mean the yeast like it.  Remember, we often ferment in the mid 60s, but if the yeast had their choice from a reproductive standpoint the temp would be more like 85 or 90F.

[phillamb168]

Related to this, can someone remind me what the thing is called that you put on a corny gas out valve to regulate the pressure inside? Setting it to 15 PSI and then it vents when it goes over, until it goes back down to 15?

I typically ferment all of my lagers under some pressure, because I have to ferment them in cornies (not a very big fridge, only two will fit, carboys don't fit, etc). I would be very interested in seeing how fermenting under pressure at ale temps would affect ales. Perhaps a fun exbeeriment?