Fermenting under pressure

[dfhar]

Given that we know that the same strain of yeast behaves quite differently from the homebrew setting in the higher pressure environment of a commercial-scale fermentation tank, I wonder how close homebrewers can get to cloning many commercial examples, even when using the same yeast.

I've been thinking lately about using corny kegs with shortened dip tubes for my primary fermentations so that I can have a completely closed system post-fermentation. I brew in 3.3 gallon batches, so 5 gallon kegs are perfect for this. Another advantage of this system is that I could experiment with pressurized fermentations. What I'm thinking is that after I pitch my yeast, I seal and pressurize the keg, then attach a relief valve set to the same pressure to the keg's gas-in post. The valve would serve as an airlock while also maintaining the pressure inside the keg. Pressurizing the keg to somewhere between 4 and 8 psi should mimic the environment that the yeast are subject to in a 15 to 20 foot deep cylindroconical fermenter.

Has anyone tried anything like this?

 

[flugelizor]

That's thinking outside the box.
You will want three of them:
0 - psi
3 - psi
5 - psi

Or something like that.
Except there are some things you cannot replicate.
For instance I imagine the CO2 creates currents, which are constantly moving the beer from 0 psi to maximum psi in the larger system.

 

[dfhar]

True, there are other factors like internal currents inside the fermenter. I believe the largest of these arises from the temperature difference between the column of liquid in the middle of the fermenter (warmer) and the ring surrounding it (cooler). Warmer beer flows up through the center of the fermenter, then cools and falls back down along the sides to the bottom of the tank. You'll still get those kinds of currents in a homebrew system, but they may be slower moving due to the smaller temperature gradients that exist in a narrower fermenter.

Further, I agree that pressurizing the keg's headspace with CO2 won't produce exactly the same kind of pressure gradient that exists in a tall fermentation tank, so the flow of beer inside the keg may not even matter much. At best you can make your keg look like a horizontal section (whose thickness is equal to the height of the liquid in the keg) of a taller tank, where the depth offset of the section into the tank is determined by the gas pressure in the headspace. That said, I suspect that choosing a pressure to mimic a section taken from the middle of a large fermenter would work well. I expect I would need to experiment with different pressures to see what works the best.