Pressure limit for fermentation

[Sir Brewsalot]

Hi all,
I've been playing around with naturally carbonating my beers by capping the unitank a couple of days into the ferment. So far, the results have been pretty positive, saving me a few trips to get the tanks refilled, and I haven't seen any difference in how well the yeast attenuates... not yet!

I know that with higher pressures in the tank, I'll eventually begin to limit the yeast's ability to ferment out, but what's the high end limit I should stay under?

Thanks!
Scott

[lhall]

We played around with this as well, and I just want to mention one problem we had with filtering the beer from the unitank under pressure to the brite tank. We found that any pressure changes on the unitank during filtration would rouse the yeast and wreak havoc with the filtration. So we had to use CO2 to maintain head pressure on the unitank, which to me seemed to be just as much of a waste as the CO2 we would have to use to carbonate the beer in the brite tank. We quit capping off the unitanks, and had much easier filtrations as a result.

Depending on the yeast strain, you might have problems with sulphur in the final beer if you cap off too early. Our hefeweizen yeast has this characteristic.

Cheers,

Linus Hall
Yazoo Brewing
Nashville

[Sir Brewsalot]

I don't filter, but have also noticed a messier transfer from a pressurized unitank - I just assumed it was for other reasons (like my inexperience!).

I agree that putting more CO2 on it seems like I might as well force carbonate... Maybe if I time my following ferment with the transfer, I can use the blow off from that batch if it's the same beer. There's got to be a better way though.

I'll watch for the sulphur notes... I'm running Wyeast 1272 in an IPA, so I don't know if the strain has the same tendency.

Thanks,
Scott

[pbutlert]

I am assuming your brite tanks are under pressure when you are filtering? I cap off the fermenters about 1.0 degree plato above the target terminal gravity, using a pressure relief set at 10 psi. This is maintained throughout coditioning and aging. Brites are cleaned and sanitized under pressure, and are topped off to 10 psi before filtration. An air hose is then connected to the brite, with the other end going to the fermenter. As the brite fills, the excess pressure goes to the fermenter, maintaining head pressure and keeping CO2/yeast/etc. in suspension. Uses no bulk CO2, usually nets +/- 2.5 volumes, which is then adjusted accordingly. DO NOT try this on any vessel without a PRV valve.
Cheers!

[Brewdoctor]

What pbutlert refers to is often called a balance line. Balance lines can be dedicated stainless hard pipe or lengths of properly banded and appropriately pressure rated hose (often Tygon; either case 15 psi minimum). Bunging fermenters at 85 to 95% attenuated has merit and can generate free pressure for yeast drains and approximately 3 to 5 pounds at the point of transfer; assuming the BBT is pressurized to 15 psi before the start of the transfer, a balance line is beautiful and simple way to reuse CO2 for any size brewery. Balance lines are always cleaned, sanitized and purged before each transfer. Gas transfer is predominantly from BBT to FV although there could be instances of the other way around, e.g., sudden filter blinding, etc.
Once you go balance you'll never go back.
Cheers! --El Brewdocto

[gitchegumee]

And don't forget that unless your tanks are ASME rated for higher pressures, the maximum allowable pressure for any tank is 15 psi; and ALL pressurized tanks (or tanks which could become pressurized) should have a pressure relief valve (preferrably one which acts as vacuum relief as well). Keep safe! Good luck.

[The Gooch]

You should have no problem carbonating your beers without going over 15 psi.

As for possible attenuation issues try doing a forced fermentation test. As soon as you put a beer into your fermenter, take a sample, add extra yeast and have it ferment at or above room temperature. A stir plate would also help speed the fermentation of the sample. The idea is to have your sample ferment faster then the beer in your fermenter so as you can see the possible attenuation of your beer before its actually done. A forced fermentation should give put you in the ball park of where the beer should finish at under ideal circumstances. Compare a forced fermentation with the same beer under pressure to see if there is a large difference in attenuation.

You may have less usable generations out of your yeast by placing it under pressure but most craft brewers use their yeast for far too many generations anyway.

Natural carbonation may not save much co2 as you will have to counter pressure filter or rack your beer, but thats not really the point anyway. Brewers take great pride in making a natural product then have no problem in forcing co2 into it out of a tank. Thats not natural and is kind of crude and primative. It's about as natural as soda pop. Just remember where your bubles come from, nature or a out of a cannister.

[Sir Brewsalot]

This may not be what your stating (so pls. forgive if not)... but as far as I can tell, carbonation is carbonation regardless of it's source. I've not yet heard any legitimate difference between beer carbonated naturally vs. beer that's force carbonated - then again, I've not yet heard this group weigh in on the topic, so I may be on the verge of "getting my mind right"!

I'm just looking to use less gas: save some ozone, a few trips to the welding supply shop, and some time.

Thanks,
Scott

[reinheits1516]

You will get some comments on natural vs. force carbonation. In my opinion there is a difference. What I have noticed is that force carb beer tends to have a harder/sharper bite whereas natural carb beers tend to be softer and more rounded. Though not the same, think of cask beer vs. package beer. You can do a small trial for yourself by krausening (adding wort or dextrose to) one lot and forcing another. I know it is difficult to achieve equal carbonation levels (choose the natural carb as your reference and make the force carb match), but even if they are relatively close, I think you will notice a difference.

[The Gooch]

I may have come off a bit crass in my first posting regarding natural carbonation. Not everyone, (in fact most craft brewers) are set up to naturally carbonate their beer. Nor have most worked with people who have in order to gain the experience or appreciation of natural carbonation. Its quicker, cheaper, and easier to have a carb stone and "juice" up a beer with tanked gas.

I drink and enjoy forced carbonated beers but I agree with the previous posting in that naturally carbonated beers have a finer bubble and less prick than the alternative. Plus they can be 100% natural, not just mostly pure.

Naturally carbonated beers may potentially have better head retention as some of the head forming proteins are not bubbled out, which can happen depending on technique of forced carbonation.

To mimmick natural carbonation, head pressure can be used which I have heard yields a smaller bubble. Loosing the lower molecular weight head forming proteins should not be an issue with this technique.

A couple of more thoughts. Even with carb stones a lot of brewpub beers are greatly under carbonated. I like cask beer fine but even cask beer is not flat. Artificial vs. natural? Both can be used in great and crappy beers. But one is a little more refined, thats all.

[BigWilley]

One issue with carb stones at least in my experience is that if your not careful you can scrub hop aroma right out of your beer. If you go through the trouble of dy hopping an IPA only to scrub out most of the aroma it can be frustrating. That said I naturally carbonate and then use a carb stone inline during filtration if i need extra carb. Also Filtering a beer thats been dryhopped kills lots of aroma to, but usually i am forced to filter my IPA's due to hop pellet flakes that wont settle.

[Tbrew]

Interesting thread. To speak to the original issue on fermentation performance if you look at this article in the MBAA TQ you will find a good examination of the effects of CO2 on fermentation http://www.mbaa.com/techquarterly/ab...5/tq95ab27.htm . In the experiment 1hl batches were fermented and at 50 hours fermentation (at 12C and out of 200hours total) one batch had 21psi top pressure put on. After this point CO2 in solution in the atmospheric tank was 3g/l (~1.5vol) and the pressurized tank was 6g/l(~3vol). The fermentations were essentially equal in cell count and attenuation rates. What did change was the esters with the pressurized tank being less (note diacetyl typically is higher with pressure fermentations). So for small brewers this would seem to show that top pressure is OK for fermentation if you the lost of some esters is acceptable.

CO2 becomes much higher in tall tanks. Here there is greater hydrostatic pressure and CO2 is dissolved at much higher levels all other things being equal. A 20m tall FV at 2C with top pressure of 17psi has about 3.18vol-co2 while a 2m tank with the same top pressure would only be about 1.86 vols. . Enough to suppress fermentation? I’m not sure since with a quick look I couldn’t find a claim that CO2 inhibits fermentation in regards to apparent extract reduction. Can someone cite a source for this?

Here is a thread about closing tanks to harness CO2 http://probrewer.com/vbulletin/showt...=&threadid=919 . This practice is just good sense. You are saving money and being less wasteful (you paid for the malt you might as well get your money’s worth). As far a foaming during transfers you need to use proper pressures to keep CO2 in solution as suggested above forumers. This includes filtration where if foaming occurs through the filter bed then back pressure on the filter needs to be raised. DE etc. should not have to cause foaming.

As far a CO2 taste quality from compressed cylinder or “natural” CO2, that is a new one to me. Certainly if you krausen or bottle condition a beer you will have different flavours for many reasons. I would argue that taste differences are attributable to the process and not the CO2 and as suggested above there can be good “naturally” carbonated beers and bad ones. Check out Charlie Bamforth’s recent article on Beer Foam Excellence for the IGB/IBD journal. In it he spells out the physical factors of foam, and no where is there a discussion of the source of CO2 and that includes finer bubbles. Again the factors that yield finer bubbles are not the natural carbonation itself but the associated factors with bottle conditioning (the beer being unfiltered being the big one…smaller nucleation sites (haze is really small) is the biggest factor in bubble size).

Hopes this helps.

[MikeJordan]

There is also a nice article in the March/April 2002 issue of The New Brewer. The title-More Beer to the Bright Tank: Pressurized Fermentation Reduces Beer Losses. This was a presentation at the 2001 CBC in Portland presented by Matt Swihart from Full Sail Brewery.

I generally think pressurized fermentations will cause many noticeable differences in ester production that may change the sensory profile of the beer. Most likely SO2 levels will be higher, but may be OK with some yeast strains and some beer styles. I would suggest some experimental trials and start on the conservative side. See if a taste panel can detect differences. You may find a low level of pressure such as 2-3 psi will work without altering the profile of the beer. Good luck!

[Sir Brewsalot]

Just a follow-up to this thread... I've been capping my fermenters for a while now, capturing most of the CO2 I need for kegging off (except when I use that fermenter with the leaky gasket, in which case I get NONE. Grrr...).

The side benefit I'm seeing is in aroma. Instead of walking into the brewery and finding the room filled with the wonderful smell of (in the case of my stout) molasses+hops, I have a modest aroma there, but a noticably bigger aroma in the finished product.

Do you think this is imagined (since without a triangle test, it's pretty subjective - and I haven't set one up yet), or maybe it's that I'm NOT bubbling off the aromatics in the fermenter, much the same way we talk about bubbling them off when force carbonating w/a stone?

Thoughts? Did that even make sense?

Great help guys. I owe each of you a beer next time you're in this neck. Now I gotta get me some more hose for that balance line!

Cheers,
Scott

[Brewdoctor]

Have you ever noticed how an overly vigorous violent fermentation seems to negate the aroma additions made in the kettle? If a batch is over-pitched and/or ferments out in one day then kettle additions are compromised. Similarly, if beer is foamed excessively then dry hop and any remaining kettle hop character is scrubbed out. This happens with in-line carbs and stones--where I'd like it to happen is in the pint glass--that wonderful aroma wafting off a creamy head.
About all you can do is manage cell counts, dry hop at terminal gravity (and put pressure on the tank immediately after) and then handle as gently as possible after that, where it will get the biggest blow dealt to the final hop character. In an ideal world where time isn't money I would bung fermenters and let them sit cold for as long as possible and then in the BBT use headspace top pressure. Sure it takes a million years but seems to produce a similar softness as with bottle conditioned. And all those hop notes are just locked right in....

Other solutions include up the hops to compensate for future loss (which is not recommended due to consistency issues) or enjoy with a little less carbonation (e.g., casks). Of course some people might just chuck in some oil at a late stage but that's far from le natural.