Open Fermented Weizen

[Bobby_M]

There's been plenty of discussion regarding open fermentation's effect on ester expression across any style that benefits from pushed esters. It's been way more popular lately to talk about pressure fermenting to have the opposite effect (ester suppression). Anyway, one thing I didn't find was any experimentation on fermenting under a vacuum to even further accentuate ester expression. I'm in the middle of a comparison between a standard ferment with a tall fermenter and a blow off tube submerged in about 10" of water depth and a somewhat open ferment using a foam stopping in a "wide" fermenter. This is day 5 and planning to swap the foam stopper "open ferment" one over to a closed lid and a healthy long CO2 purge. Note that the full fermenter is a 3 gallon and the more empty one is a 7 gallon. The beer volume is the same, 2.75 gallons.

While I expect a noticeable difference in banana esters between these, I am more intrigued by the idea of holding a partial vacuum to make it go even further. I actually just got a vacuum pump for a different project and I thought of maybe trying it by pulling a vacuum on an empty half barrel sanke keg on a cycle time to maintain the vac. The one thing I'm trying to figure out is if there's a way to use a blowtie or pressure regulator to meter the vacuum. I'm so used to thinking about pressure that I'm blanking out on how vacuum behaves.

 

[Red over White]

This is very interesting. What is the vacuum pump rated to in inches of water or inches of mercury?

A simple vacuum breaker can be fashioned, but would need to be incased in a way that when it trips, it doesn't allow air in, but nitrogen or co².

 

[Red over White]

If you don't care about safe guarding the vessel, the vacuum relief can be on the vacuum line going to the vessel.

 

[Red over White]

Here's a simple example of a never fail mechanical vacuum relief for a Roots 56 blower. It's a bolt with a washer on the inside that covers the holes. The tripping point is adjustable by the tension on the spring.

 

[Bobby_M]

If you don't care about safe guarding the vessel, the vacuum relief can be on the vacuum line going to the vessel.

The pump can pull something like 28HG so I'm not comfortable pulling that on a glass carboy.

 

[Bassman2003]

Cool stuff Bobby. I ferment in a Kegmenter, so this would be an option if it works. Holding the vacuum might be tough once the yeast start creating a lot of CO2 pressure outward. The setting of the vacuum pump needs to have some headroom to work past the increase from the yeast production.

Also, would the vacuum port actually suck up krausen as it rises to the top? Awkward concept is this would not be a static environment!

 

[Red over White]

The pump can pull something like 28HG so I'm not comfortable pulling that on a glass carboy.

That's a LOT of vacuum. 16hg will crush a 55 gallon SS drum instantly, ask me how I know lol. At a certain level of vacuum fog is immediately created inside the vessel. I would recommend very low levels of vacuum and a very sturdy vessel inside a garbage bag as a containment field during trials with water.

 

[AlexKay]

If I remember correctly (and I'm getting old, so I may not) this podcast did cover fermentation under vacuum a bit. The links lead to a paywall, unfortunately.

As I understand it, the important thing to control is the concentration of dissolved CO2, which conveniently is linearly proportional to the partial pressure of CO2 in the headspace. In a closed fermentation you end up with a more-or-less pure CO2 atmosphere inside the fermenter, at 1 atm if you've got an airlock or blowoff tube, or above that if you're pressure fermenting with a spunding valve.

If you can do an open fermentation where the air above the fermenter is well mixed, you get the CO2 partial pressure down to the ~400 ppm present in the atmosphere. That's orders of magnitude lower than in a closed fermenter, and actually probably rather better than you're going to do with any vacuum pump you'd be able to afford and operate at home (and be compatible with food.)

My guess is that mixing doesn't happen quickly enough under normal conditions to get you down to 400 ppm. (I will not say the words "CO2 blanket.") I suspect forced air movement would lower your CO2 partial pressure more than any vacuum pump you hook up.

 

[Bobby_M]

I tend to lean on pragmatic experimentation so it's something I'd still want to try. I'm sure CO2 does have a role, which is why tall narrow fermenters would suppress esters as more CO2 would be in solution. Pulling vacuum on the headspace would tend to rip CO2 out of solution right? Same concept as reducing the depth of beer in a fermenter.

My intent would be to pull something like a -20HG on a sanke and then have a regulator between that and the fermenter set to hold something like a -2HG vacuum on the fermentation the whole time. I'm confident that I could time cycle the pump for something like 20 seconds of run time each 30 minutes or something like that to maintain a good vacuum on the Sanke "vacuum reservoir".

I think a simple blowtie between the fermenter and the sanke, being careful to position it with the proper gas flow direction, would do the job but I'm way out of my depth here. I think the changing vacuum on the output side would cause weird results since a regulator like the blowtie vents in reference to 1ATM usually.

 

[Bassman2003]

Interesting discussion. With pressure fermentation, there is more CO2 present as it is being forced to stay. With the inverse, would there be any more CO2 to evacuate compared to normal atmospheric pressure? The yeast create it but how much stays in solution during a "normal" ferment? Probably not that much to suppress ester production. I agree with Alex but still very cool to try. One never knows. Sensory is tough to compare to without a control beer. Just be careful and looking forward to hearing the results!

 

[AlexKay]

I tend to lean on pragmatic experimentation so it's something I'd still want to try. I'm sure CO2 does have a role, which is why tall narrow fermenters would suppress esters as more CO2 would be in solution. Pulling vacuum on the headspace would tend to rip CO2 out of solution right? Same concept as reducing the depth of beer in a fermenter.

My intent would be to pull something like a -20HG on a sanke and then have a regulator between that and the fermenter set to hold something like a -2HG vacuum on the fermentation the whole time. I'm confident that I could time cycle the pump for something like 20 seconds of run time each 30 minutes or something like that to maintain a good vacuum on the Sanke "vacuum reservoir".

I think a simple blowtie between the fermenter and the sanke, being careful to position it with the proper gas flow direction, would do the job but I'm way out of my depth here. I think the changing vacuum on the output side would cause weird results since a regulator like the blowtie vents in reference to 1ATM usually.

One thing that might seem counterintuitive (but is still true) is that open air is a pretty good vacuum as far as CO2 is concerned: partial pressure is 0.0004 atm. The presence of 0.78 atm of nitrogen and 0.21 atm of oxygen makes no difference as far as CO2 going into or coming out of solution.

The vacuum reservoir idea is workable. I think a keg will hold a vacuum, but generally speaking you can't assume that something designed to be pressurized will function with the pressure differential going the other way. Proceed carefully.

The blowtie (oriented correctly) will work, though it may be less fiddly if you work at a few psi instead of ~1.

Many vacuum pumps will not hold pressure when they are off, so cycling the pump on and off may not work without valving it off at the same time.

 

[mac_1103]

The yeast create it but how much stays in solution during a "normal" ferment?

0.86 volumes at 68F according to most of the priming calculators I've seen.

 

[Witherby]

I am in the middle of planning a Hefeweizen brew day so I have been deep in research. Jeff Alworth talks about open fermentation in a few of his books. In the Beer Bible he says:

“Weizen yeasts also have a special ability to turn ferulic acid into a phenol that gives the beer its spice. They are more able to produce this phenol in the presence of oxygen, which is why open fermenters are so vital.
Open fermenters help in other ways, too. Esters…also form during open fermentation. In studies measuring phenols and esters, researchers found that fermenter shape has a pronounced effect on both groups but especially on esters. In open fermenters, beers developed about 50 percent more phenols than in tall, enclosed cylindro-conical tanks. Amazingly, the ester responsible for the banana flavor (isoamyl acetate) was produced at more than double the amount when an open fermenter was used.”

All this to say I am curious if the phenol production will be less than optimal in a vacuum due to the decreased oxygen exposure and whether oxygen exposure plays a part in ester formation, or if that is merely due to the decreased pressure and CO2 exposure. You might get a banana bomb and no clove. I can’t wait to hear the results.

 

[Bassman2003]

I was thinking on this. For those of us who do not have a Yorkshire Square to ferment in, instead of using a vacuum, what about just putting a computer fan over the opening of our vessels? My Kegmenter has a 4" opening. So if I only just leave it open, a lot of gas is just going to stay down in the fermenter. But if I put a computer fan blowing outward over the opening it would circulate a lot more gas and move more CO2 out of the headspace. This would not take away the .86 vol of CO2 in the wort though.

Then there is the approach of pressurizing with air instead of CO2. A lot of variables of which I look forward to exploring!

 

[Bobby_M]

One thing that might seem counterintuitive (but is still true) is that open air is a pretty good vacuum as far as CO2 is concerned: partial pressure is 0.0004 atm. The presence of 0.78 atm of nitrogen and 0.21 atm of oxygen makes no difference as far as CO2 going into or coming out of solution.

The vacuum reservoir idea is workable. I think a keg will hold a vacuum, but generally speaking you can't assume that something designed to be pressurized will function with the pressure differential going the other way. Proceed carefully.

The blowtie (oriented correctly) will work, though it may be less fiddly if you work at a few psi instead of ~1.

Many vacuum pumps will not hold pressure when they are off, so cycling the pump on and off may not work without valving it off at the same time.

My concern is more about oxidation. I want to remove the CO2 while not bringing O2 in.

I know a sanke will hold at least -20 because there's a video of a guy on youtube holding -29. I plan to put a check valve between the sanke and the vac pump.

 

[odie]

I recently did an "open" fermentation. I can't recall if is was a hefe or saison...I have both on tap right now. Basically I left the keg lid off for the first few days but had a mess bag in place to keep anything from dropping into the beer.

But since I don't bottle, I'm not able to hold a sample from the previous batch to direct compare to the current batch on tap.

 

[Bassman2003]

I do not think Oxidation is an issue until the end of fermentation. The active yeast will eat it all of the O2 before it can do any damage. I think you would be ready to close it up and spund at about 1.020 in order to create the CO2 environment.

 

[Bobby_M]

There's been plenty of discussion regarding open fermentation's effect on ester expression across any style that benefits from pushed esters. It's been way more popular lately to talk about pressure fermenting to have the opposite effect (ester suppression). Anyway, one thing I didn't find was any experimentation on fermenting under a vacuum to even further accentuate ester expression. I'm in the middle of a comparison between a standard ferment with a tall fermenter and a blow off tube submerged in about 10" of water depth and a somewhat open ferment using a foam stopping in a "wide" fermenter. This is day 5 and planning to swap the foam stopper "open ferment" one over to a closed lid and a healthy long CO2 purge. Note that the full fermenter is a 3 gallon and the more empty one is a 7 gallon. The beer volume is the same, 2.75 gallons.

View attachment 820810

While I expect a noticeable difference in banana esters between these, I am more intrigued by the idea of holding a partial vacuum to make it go even further. I actually just got a vacuum pump for a different project and I thought of maybe trying it by pulling a vacuum on an empty half barrel sanke keg on a cycle time to maintain the vac. The one thing I'm trying to figure out is if there's a way to use a blowtie or pressure regulator to meter the vacuum. I'm so used to thinking about pressure that I'm blanking out on how vacuum behaves.

Well, that was a bust. The one on the right smells and tastes great and the one on the left already smells mostly like sherry. The sealed one is at 1.020 and the "open" one is at 1.018. I sealed that one and purged with CO2 yesterday. The "open" one has less banana, smells like sherry and tastes a little like soy sauce. All indicators that it's already oxidized.

 

[day_trippr]

Wow - 7 days post pitch and it's soy sauce already?

Impressive!

Cheers!

 

[Bassman2003]

Wow, that is a surprise. Maybe it would pair well with sushi? I don't think open fermentation is flawed, there must be something that happened along the way.