Is it possible to do pressurized fermentation in a mini keg?

Question

I have been keen on moving from bottles to use kegs in my amateur home brews. Due to a lack of space and because I just like the size and mobility of the smaller kegs I'd like to try to use multiple mini kegs of about 5L size for a 20L+ brew.

I read about a trick for how to force carbonate the beer in mini kegs using sodastream bottles which seemed to make for a pretty convenient process.

I have also been reading about pressurized fermentation directly in the keg as a way to remove the carbonation step from the process which seems beneficial to me.

Unfortunately I have not been able to find any good sources on if this is feasible or not. I'm assuming that a mini keg can take the pressure, considering it can be force carbonated, although it would probably need a pressure release valve so it can be kept under a certain pressure (2-3 bar?).

I'm thinking it would mean a process similar to this:

1. Brew wort.
2. Cool wort.
3. Fill mini kegs with wort, aerate and pitch each keg with yeast.
4. Fit kegs with pressure release valves set to a certain bar (and perhaps adjust over time?).
5. Let it ferment and carbonate for 2 weeks.
6. Tap the keg through a filter into glass and cheers!

I think the http://www.williamswarn.com/ uses a similar process, but in a smart little machine with built in boiler.

Would this process be even possible and what pitfalls have I not considered?

Answer 1

No, you could not use 5-liter mini-kegs for a pressurized fermentation UNLESS you could replace the top bung with something like a Spundling valve, or perhaps a cask-conditioning style bung with a shive, and then you would knock out the shive at the appropriate time with a porous spile that would allow excess gas to vent.

I can't find the pressure rating of a mini-keg, but it certainly could not contain the gas from a full fermentation, and the rubber bungs available in the U.S. do not have built-in pressure relief valves. I have seen several mini-kegs where the mini-keg bulged or the seam failed due to excess pressure, for example in this vidoe.

Something like this from the EU would work.

However, I don't think you would want to conduct primary fermentation in the mini-keg because you will end up with a lot of unwanted trub in your serving vessel.

Instead, it is a standard practice in homebrewing to use these for "bottle"-conditioning: transferring your fermented beer into a mini-keg with priming sugar, and allowing the beer to naturally carbonate, such as explained in this info sheet from Midwest Supplies.

Answer 2

Yes, this is very possible and is basically how cask ale is made, minus the fact that cask ale does not allow extra CO2 to be injected to force a bit of carbonation and push the beer out without a pump -- which you can easily do with the CO2 injector of your mini keg.

It is also exactly how the Beer Machine product works (I am not affiliated with them, just a happy customer). It's worth looking at the "instructions" booklet for that product. I have 2 of these plastic kegs and they work very well. It should be simple to adapt the mini keg to ferment and carbonate in one container the way they suggest for the Beer Machine.

The drawbacks are that you will have to monitor the natural carbonation carefully, and then clean the keg of the spent yeast afterwards. But other than that, the process is fairly simple and straightforward, assuming that you consume the beer before the yeast begins to impart off flavours, which might happen after a month or so after fermentation. But it would be hard to believe that any beer would be left in your mini keg after that amount of time...

In short, yes, it's a very traditional method and one that turns out to be simple and very efficient.

Answer 3

I have done many brews in 5L mini-kegs, but only the brightening (secondary) fermentation, not the primary.

You really (REALLY) have to make sure the primary is finished before you keg it (I leave my 50 litre brews for a full two weeks in primary), then I add 9 grams of priming sugar directly into the wee 5L kegs, top 'em up sat on a scale to weigh the contents as I fill. You can get a top valve with a pressure release, but I have never bothered. These kegs are seriously strong. I kegged a bit early once and they bent right out of shape, still didn't explode or anything, but scared the hell outta me when I saw them!

If you have got a bit too much pressure in them when you open it, you can always pull the spindle out of the keg until it is only a cm or two in, then bleed off the excess gas and refill it with fresh CO2 from the tap-server.

Alternatively, google "politainer barrier" made by Promens in Germany. This is a bag/box affair similar to what local apple juice is served from. I now use these "Cask Ale Boxes" as I call them instead of the mini-kegs as you can just bleed off the pressure, and/or try a bit, straight from the integrated tap. They come in many sizes and work out a 1/4 of the price of 5L mini-kegs (if you use a 10 litre politainer).

Cheers!