Pressure Fermentation. Does it Really Work?

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amercado58

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Hi all,

I've recently come across a number or articles and videos discussing pressure fermentation and the benefits of it, such as speeding up the attenuation process (i.e finishing fermentation much fast than normal). So I thought I would put it to the test! I brewed up two bocks using the same exact malt build and split-batched them. Fermenter #1 is a Spike Flex+ with a PRV and got 5 gallons wort. The second fermenter is an Ss Brew Bucket and also got 5 gallons of wort. The SG was 1.058 or 14 Plato. Both are in the same fermentation chamber and both yeasts were pitched at around 58 degrees or 14 c and fermented at 52 f or 11 c. Here are the changes:

Fermentation Steps:
Spike Flex+: pitched WLP#838 (Southern German Lager) using a 2L starter and using 3 packets.
Ss Brew Bucket: pitched Saflager 34/70 Bohemian Lager by rehydrating 2 packets.

Setup the day of pitch:
Spike Flex+ didn't have any blow-off tubes. I just simply pitched. PSI was at 0.
Brew Bucket: set up blow-off tube into sanitized jar.

And they are off!
Days 2-3 I saw the Spike shoot up to 15 psi. Brew Bucket was very active.
Day 3: Towards the end of day 3, in the Brew Bucket I removed the blow-off tube and added a Spunding Valve. Valve hit about 5 psi the next day.
Day 4: Brew Bucket remained at ~5psi. I consistently removed pressure from the Spike reducing it to about 10 psi. Every time I checked, it was back at 15 psi.
Day 5: Raised temp for a diacetyl rest. Toward the end of the rest, I pulled samples and ran them through coffee filters to degas and remove any yeast sediment. The results were staggering:

Spike Flex+ came in at 1.030
Brew Bucket came in at 1.014
*Measures were taken with an Anton Paar Density Meter (highly accurate).

Any ideas as to why that is? This goes counter to the literature and videos that I have seen. The only thing I can think of was the fact that I consistently (about 3 times a day) removed pressure from the Spike. Liquid vs. Dry yeast?
 
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As I understand, you used two different yeasts. One yeast per fv. That could explain the difference in gravity

Pressure fermentation reduces also yeast growth and thus can hinder fermentation. It is not surprising that pressure fermentation is doing worse under the same temperature. Usually you use higher temperatures when fermenting lagers under pressure. That's from my understanding the advantage and that's what speeds up fermentation
 
This goes counter to the literature and videos that I have seen. The only thing I can think of was the fact that I consistently (about 3 times a day) removed pressure from the Spike. Liquid vs. Dry yeast?

So first, you had multiple variables here, so this technically wasn't a valid test of pressurized vs not pressurized.

Second, I don't know what literature or videos you've been looking at, but pressure doesn't speed up fermentation. Quite the opposite.
 
for clarification, my understanding is the higher temps are what speeds up fermentation. Under pressure the yeast is strained (slowed down) and this does not produce the off flavor compounds that are are usually produced under high temps and this simulators the much longer process of lagering.

it’s an worthy process to explore is LLC you want to brew lagers in the summer and not wait until winter to enjoy.

the process also help create a no oxygen environment for heavily dry and late hopped beers like NEIPAs but often a spundling valve can be used to relieve pressure while keeping 02 out
 
for clarification, my understanding is the higher temps are what speeds up fermentation. Under pressure the yeast is strained (slowed down) and this does not produce the off flavor compounds that are are usually produced under high temps and this simulators the much longer process of lagering.

it’s an worthy process to explore is LLC you want to brew lagers in the summer and not wait until winter to enjoy.

the process also help create a no oxygen environment for heavily dry and late hopped beers like NEIPAs but often a spundling valve can be used to relieve pressure while keeping 02 out

Yes! That is what I understand, al these benefits you explained. Next time I am going to ramp up the temperature and see if that changes anything.
 
As others you have a lot of confounding variables here. My big question is how did you pressurize a brew bucket to 5psi? The website says to avoid anything above 2.

With a Spunding Valve. Once I attached it, the Spunding Valve kicked up to about ~5 psi and it didn't move. This morning I looked at it and it is completely at 0, which I am assuming fermentation, ergo, the production of c02 gases has completely stopped.
 
With a Spunding Valve. Once I attached it, the Spunding Valve kicked up to about ~5 psi and it didn't move. This morning I looked at it and it is completely at 0, which I am assuming fermentation, ergo, the production of c02 gases has completely stopped.


don't make that assumption. Since the pressure dropped it's likely the valve isn't holding pressure. A good valve will only release excess CO2. I would gather you valve was open enough to let the co2 escape below 5psi. if thats the case the teaser may still be making CO2 just not faster that the valve is realizing it. Cooling will also drop the PSI and even cause air to be sucked in like during a cold crash.
 
interesting about the pressure slowing down the yeast. I have 2 batches ferming in the kegs...I used a blow off tube until it slowed down and then capped them and have to vent the psi frequently. Perhaps I should have waited a week or more before removing the blow off tube? But I wanted enough activity still going to seal the lid. slow building psi will often not seat the lid o-ring.
 
My last batch brewed, my English IPA, I did with the spunding valve set to 14-15psi from the start. It was done fermenting in about a week (6-7 days). I use a temperature sensor to tell me when things have peaked and are slowing down. Once it hits ambient for more than a day, or two, I know it's basically done. I still give the batch some time to ensure it is done, and for the yeast to flocculate fully.

From what I had found in my searching about the process (last year) you don't need to worry about stressing the yeast until you hit above 20psi. Some can even tolerate more than that without negative effects.

IF I was to try to do a comparison test, I'd make sure every aspect of the test was identical except the one item I was trying to investigate. I sure as hell wouldn't use different yeast strains if I was trying to find out how fermenting under different pressure levels (or no pressure and pressure) effect the end result. As already mentioned, you had too many differences (yeast being the big one) to make it a valid test. IF you wanted to see how different yeasts act under pressure fermenting conditions, then you would need everything else identical except the strains used.

Seems, to me at least, that you need to do another test run but only have one parameter different.
 
I'm not intending to pile on about the multiple variables but I'll make a suggestion on what you could have done. Understanding that you may have initially meant to just compare what the two different yeasts would do and you later pivoted to trying to test pressure vs no pressure, you COULD have blended the starter and the two packs of dry yeast together into a common slurry and pitched equal amounts into both.

As others have said, the whole philosophy of pressure ferments is to be able to run the ferment at a higher temperature while the pressure suppresses the fusel and ester production that would normally occur at that higher temp.
 
As others have said, the whole philosophy of pressure ferments is to be able to run the ferment at a higher temperature while the pressure suppresses the fusel and ester production that would normally occur at that higher temp.
so are you saying that once the gas post is capped, you can move the fermenter to a higher temp place/chamber/room and not worry about it? Does the higher temps off set the slowing of the yeast that pressure supposedly causes?
 
so are you saying that once the gas post is capped, you can move the fermenter to a higher temp place/chamber/room and not worry about it? Does the higher temps off set the slowing of the yeast that pressure supposedly causes?
IME, going with <15psi (or not over) and the yeast are not stressed. Or at least not enough to cause any issues.

There are people that make lagers without chilling them by fermenting under pressure. IIRC, they also go to glass faster because of this. I'm not into lagers, but my ale yeast acts "normal" even under 14-15psi. As in going like crazy from the start and finishing in the amount of time I expect (or have experienced in the past when not fermenting under pressure).

My coming two batches are going to combine fermenting under pressure with some temperature control. I plan to keep them in the middle of the temperature range for the ferment. Or within a few degrees of it anyway. Right now my basement is a bit warmer than I would otherwise like (low 70's yesterday).
 
I've got an ale and a lager going right now. Both temperature controlled to the normal fermentation temps, not warmer. I just use a blow off tube until the bubbles slowed and then capped with a gauge. I bleed the pressure periodically back down to 10 and then let it build and bleed again. I'll start bleeding to 5. Once it stops going over 15 I'll call it good.

Or should I dial up the temps by 5-10' since they are under pressure?
 
hi
I became interested in pressure fermentation a few months back (after reading about it in this forum) as a solution to the high summer temperatures we have in south Africa, usually in the 30 + degrees centigrade. my beers were not terribly good during these months, I began with so far I have completed 3 brews with great results, I have actually been fermenting at between 20 and 28 psi which I see is not recommended by some who have posted on this thread, not sure why and I have only had great results at this pressure (2 with kviek Oslo yeast and 1 with safale 04) my question is am i pushing my luck? I arrived at this pressure due to the limitations of my setup, I simply adapted an old 50lt g type keg which was too large for my 30lt brews by welding on a pressure gauge and cheap popper valve I brought from ebay, I had to modify the valve by changing the spring and the result was around 25psi which varies according to the temperature. should I reduce this pressure? other than this I have found pressure fermentation to be a real boon to my brewing process, it also assists with kegging and bottling as the finished brew is pre gassed.
 
@dtashmore547 IMO the pressure limits are more depending on the yeast strain you're using. It's highly possible (or even likely) that what you're using is fine with the pressure levels you let them reach. Especially if you're getting great results.

The yeast I'm using lists their happy temperature ranges as topping out at either 74F or 75F. My plan, for the next two brews, is to use the glycol chiller to have them not exceed ~72F. Since I expect the basement to exceed that temperature at some point during their fermentation cycle, I'll have the chiller connected to the chill coils. I'm also planning to have the spunding valves set to lower pressure levels than I've done so far. More to see how that effects the end product. These are not recipes I've made before, so I don't have any control brews to compare against. More of a curiosity item for me. I plan to have the stout at a higher pressure limit while the best bitter will be at a lower level.
 
All this talk of pressurized fermentation made me think of a work project I did about 10 years ago with a high pressure vessel used for nano imprinting experiments. We first tried to maintain the 2000 psi with a mechanical regulator but it had way too much hysteresis. We solved the problem by having a PLC control a solenoid valve to bleed off pressure through a needle valve, basically a software controlled pinhole leak coupled with a controlled pinhole fill valve. I bet I could make an electronic spunding valve using the same concept.
 
My last batch brewed, my English IPA, I did with the spunding valve set to 14-15psi from the start. It was done fermenting in about a week (6-7 days). I use a temperature sensor to tell me when things have peaked and are slowing down. Once it hits ambient for more than a day, or two, I know it's basically done. I still give the batch some time to ensure it is done, and for the yeast to flocculate fully.

From what I had found in my searching about the process (last year) you don't need to worry about stressing the yeast until you hit above 20psi. Some can even tolerate more than that without negative effects.

IF I was to try to do a comparison test, I'd make sure every aspect of the test was identical except the one item I was trying to investigate. I sure as hell wouldn't use different yeast strains if I was trying to find out how fermenting under different pressure levels (or no pressure and pressure) effect the end result. As already mentioned, you had too many differences (yeast being the big one) to make it a valid test. IF you wanted to see how different yeasts act under pressure fermenting conditions, then you would need everything else identical except the strains used.

Seems, to me at least, that you need to do another test run but only have one parameter different.

What temperature are fermenting? I'm really interested in pressure fermentation because of my lack of cold-side temperature control. I live in a small NYC apartment with wife and kids - I can only have so much equipment! I'm doing 2.5 gallon batches and want to do 5 gallon. I can temp control a small fermenter in a thermal bag with frozen plastic water bottles (It works really well). 5 Gallons will fit my thermal bag, but I don't think I can get the temp low enough for normal fermentation. I can probably keep 5 gallons in the low to mid 70s with my set up. Also, if you are fermenting at 14-15 PSI isn't that carbonated? Can you bottle or keg right from the fermenter?
 
Also, if you are fermenting at 14-15 PSI isn't that carbonated? Can you bottle or keg right from the fermenter?

14 PSI at room temp (say 70F), reaches equilibrium at a little less than 1.6 volumes of CO2. To get to, say 2.5 volumes, you'd need about 29 PSI.
 
I’ve had really great luck with pressure fermentation. I’ve used kveik (to reduce that orange Esther), s-05, abbaye, and some others. Recent did a porter with London that got up To 90F because of a summer heat wave. I thought it was going to be a hot fusel mess, turned out fine. I typically ferment at 10psi.
 
From what I've re
14 PSI at room temp (say 70F), reaches equilibrium at a little less than 1.6 volumes of CO2. To get to, say 2.5 volumes, you'd need about 29 PSI.
So, I have a few 2.5 gallon kegs, I use sodastream tanks for dispensing but not force carbing, I prime. How do you handle carbanation? You're over halfway there it looks like. How do you finish off the priming?
 
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