Pressurized fermentation.

[manticle]

Not sure if this is allowed but anyway

This post on another forum

Totally allowed mate. The rule I think you are referring to is about active links IN SIGNATURES to other brewing forums. You can (and should always be allowed to, in my view) post useful links about topic relevant material, whether or not that link goes to discussions on a different forum or not.

 

[wobbly]

The yanks are using 15.5 gal kegs so about 58L so a 50l keg posses the problem of reduce head space, in a conical they say to leave or account for 20% head space, so for a double batch its cutting a little close though I guess there's only one way to find out.

In the thread I linked to overcome the lack of head space in the 15.5 gallon keg when fermenting close to the keg limit some have linked a standard 19lt keg half filled with water (so as to reduce the head space back to acceptable volume) in series with the fermenting keg and installed the relief valve on the 19lt keg and fermented a large batch (double) that way

Cheers

Wobbly

 

[Beerisyummy]

So are you saying you had *less* esters in the final beer?

I read something about open fermentation (for wheat beer) the other day.
The author suggested open fermentation produced more esters, and thus it seems to line up.

Yes, I would say there were less esters in the final beer. It was still drinkable, although I'd not make a habit of that particular process.

In regards to the open fermenters, there are so many variables it's not funny. My take on most things I've read is that the FV design will impact on the way the yeast does it's thing.
I'd imagine that an open fermenter, with a good amount of surface area, would keep the amount of dissolved C02 (in solution) down. That should help the yeast go crazy, and create plenty of funk.
Alternatively, you could also up the temperature a little for a similar result.

Pressurized fermentation is just another way to manipulate the way the yeast behaves. It won't stop you needing to age a beer or fix other problems.
The carbonation and transfer part of the setup is the winner for me.

 

[Not For Horses]

Was reading this little article
http://www.professorbeer.com/articles/esters.html
and came across the following:

" 3. Fermenting under pressure, as some lager brewers do, will decrease esters by decreasing the rate of yeast growth, thus decreasing the fusel precursors."

 

[MastersBrewery]

NFH I think the polar opposite is higher ferment temperatures, thus balancing pressure v temperature. I don't think it's going to be a case of one set of parameters fits all, it may well be the case that each strain will have it's own "sweet spot" while parameters for ales may all group similarly as apposed to those for lagers.

 

[Not For Horses]

Reading on from there he says that most home brewers and craft brewers lack the equipment to ferment under pressure.
So I think he actually meant larger brewers rather than lager.

 

[dent]

will decrease esters by decreasing the rate of yeast growth

I don't think this is correct. Yeast do not start generating large amounts of CO2 until after the growth phase, thus, no pressure at the growth stage.

Plus I start all my pressure ferments very cold to avoid the yeast growth generated off-flavours. Only once the CO2 pressure starts to come up do I ramp up the temperature and get it the ferment going full bore.

 

[Not For Horses]

There's pressure at the growth stage if you pressurise your FV when you pitch.

But I don't think he has the whole story anyway.

 

[dent]

Yeah but I don't think it is why the pressure ferment works, so it would be pointless. I use that time to pressurise the vessel with oxygen anyhow.

 

[Liam_snorkel]

pointing out the obvious here, but large scale brews would be under head pressure from the start due to the volume of liquid above the (bottom fermenting) lager yeast.

 

[dent]

Head pressure, sure, but the quantity of dissolved CO2 in the wort would not be increased as a result.

I'm making the assumption here that the dissolved CO2 interacting with the yeast is what makes the pressure ferment effective - I've yet to hear anything that would say otherwise.

 

[Not For Horses]

True, but it doesn't account for reduced ester production with an ale yeast.

 

[Liam_snorkel]

this is where we need a microbiologist to step in and tell us what the effect of hydrostatic pressure is on yeast regardless of CO2 content.

 

[gordo_t]

Yeah but I don't think it is why the pressure ferment works, so it would be pointless. I use that time to pressurise the vessel with oxygen anyhow.

How much pressure are you using (with oxygen) initially??

 

[Not For Horses]

dissolved CO2 interacting with the...

Hmmmm. Now this has got me thinking about carbonic acid.
And the hydrolysis of esters.
And how esterase will be affected by the presence of a weak acid.

Much beard stroking and head scratching to be done now...

 

[dent]

CO2 interaction makes sense to me as it is a waste product of the yeast after all. I would guess changing the concentration in the wort makes a difference to cell wall transports etc.


With pure O2 I was putting in about 15-20psi, with air about 40psi. The increased pressure allows me to get much more dissolved oxygen than you would otherwise obtain with atmospheric air. I don't bother with air stones, I just shake the vessel upfor a bit while it is pressurized. I'm quite sure this gets me up to the ideal dissolved O2 range.

 

[gordo_t]

so are you using something similar to the keg chargers (co2) but switching it out for an oxygen canister instead, like one of the welding ones?

 

[dent]

Yeah, just a gas disconnect which attaches to either the regulated O2 cylinder, or the compressor.

Pure O2 is completely unnecessary in this configuration in my opinion, and I'll be bringing my cylinder back to BOC soon as I get around to it.

 

[Beerisyummy]

I don't think this is correct. Yeast do not start generating large amounts of CO2 until after the growth phase, thus, no pressure at the growth stage.

Plus I start all my pressure ferments very cold to avoid the yeast growth generated off-flavours. Only once the CO2 pressure starts to come up do I ramp up the temperature and get it the ferment going full bore.

Depending on how you pitch, I don't think pressure( on our gauges) always equals the effect of co2 in solution. The lag phase will always overlap the growth phase.
I know you're not saying it doesn't, but I'm thinking that a fair amount of CO2 gets absorbed in the still liquid, which does come into play early on.

 

[dent]

Yeah, but if there is no increase in pressure, how is it different from normal open fermentation at that point in time? CO2 will be in saturation at that point either way.