Force carbonation's effect on flavor

[xico]

In meeting a veteran brewing chemist at his R&D playground briefly he commented on the importance of getting as much CO2 from the yeast as possible to protect the flavor compounds.

I don't understand how the entry of CO2 into solution would have an effect on the volatization of aromas/flavors.Can someone give me an answer as to how this is happening?

 

[doug293cz]

I think he's talking about fermenting under pressure so that a large fraction of the CO2 generated will stay in the beer, and not "sweep" out aromatics as it exits the beer. This really won't work very well as fermenting 5 gal of 1.040 OG wort down to 1.010 FG will create about 76 gal of CO2 at 1 atm pressure. If all that stayed in the beer it would be more than 15 volumes of carbonation, so you have to let most of the CO2 out anyway, and most of what could get swept away will get swept away.

Brew on

 

[xico]

Yes, after the first 3-4 days, he pulls the trub off the bottom, dry hops, and begins adjusting a PRV at the end of the CIP arm to handle increasing amounts of pressure (~7 PSI if I remember correctly). He said he doesn't keep all or most of the CO2 but he aims to yield 30-50% of the carbonation from yeast.

Thanks for the input!

 

[55x11]

In meeting a veteran brewing chemist at his R&D playground briefly he commented on the importance of getting as much CO2 from the yeast as possible to protect the flavor compounds.

I don't understand how the entry of CO2 into solution would have an effect on the volatization of aromas/flavors.Can someone give me an answer as to how this is happening?

CO2 is CO2. It doesn't matter if it's produced by yeast, or by force carbonation.
Some people swear that "naturally produced CO2" beers (through yeast fermentation) taste better than forced-carbed beers, but there is NO reason for why this should be the case, except that "naturally carbed" beers will be conditioned for a lot longer (extra week or two, at least).

 

[ajdelange]

Yes, CO2 is CO2 but it is also true that the flavor compounds mentioned in the first post are the flavor compounds, many of which are volatile and not all of which (those responsible for Jungbuket) are desirable. The object is to let the natural carbonation, that from the yeast, scrub out the Jungbuket while leaving the desirable volatiles in the beer. Allowing more of the CO2 than is necessary to remove the Jungbuket will also remove some of the desirable flavors. You can get back to carbonated beer by replacing with CO2 from a bottle but you cannot replace the flavor volatiles earlier scrubbed out. You may, OTOH, be replacing those with unpleasant aroma/flavor compounds from the CO2 source. Many beer afficionados use a carbon filter in their gas lines for this reason.

 

[xico]

CO2 is CO2. It doesn't matter if it's produced by yeast, or by force carbonation.
Some people swear that "naturally produced CO2" beers (through yeast fermentation) taste better than forced-carbed beers, but there is NO reason for why this should be the case, except that "naturally carbed" beers will be conditioned for a lot longer (extra week or two, at least).

True, CO2 is the same compound in beer from the yeast or force carbonation. What ajdelange mentioned is more what I'm getting at. You want to get your yeast to expel the undesired compounds through primary fermentation. Yeasts are all different and timing varies, but it seems like this brewer seeks to strike a balance between scrubbing unwanted flavor/aroma products from the yeast and malt, and capping the last remnants of CO2 made by the yeast to limit loss of desired cones.

He also commented on the bubble qualities later on and I was unclear as to whether this was connected to the same subject or another part of his process. There were a lot of things to geek out over and I was distracted by the Meura mash filter in the same room.

 

[techbrau]

CO2 is CO2. It doesn't matter if it's produced by yeast, or by force carbonation.
Some people swear that "naturally produced CO2" beers (through yeast fermentation) taste better than forced-carbed beers, but there is NO reason for why this should be the case, except that "naturally carbed" beers will be conditioned for a lot longer (extra week or two, at least).

Actually, it does matter. While you're correct that one molecule of CO2 is equivalent to another, there are two caveats you've ignored:

1) Scrubbing of desirable aroma compounds out from the beer like AJ has already described (so I won't go into more detail)

2) Purity of the CO2 source. Believe it or not, most CO2 that homebrewers buy is only food grade, rated to 99.9% purity. That's actually not very pure at all, and there are a lot of other trace gases mixed in with that CO2. Typical oxygen content in food grade CO2 is between 30 and 50 ppm; in other words, force carbonating to 2.5 volumes actually forces oxygen into the beer, on the order of 0.15 ppm or more. For comparison, the most widely accepted commercial bottling standard is under 0.1 ppm and I know that the better brewers like The Alchemist take this very, very seriously.

The hops you used to make your latest IPA have a shelf life of a year or more in the nitrogen purged bags they come in, but I always hear people complaining that their hop forward beers start losing aroma after a month in the keg. Oxygen is the primary driver of beer staling, and force carbonation can be a very significant source of it.

 

[doug293cz]

Actually, it does matter. While you're correct that one molecule of CO2 is equivalent to another, there are two caveats you've ignored:

1) Scrubbing of desirable aroma compounds out from the beer like AJ has already described (so I won't go into more detail)

2) Purity of the CO2 source. Believe it or not, most CO2 that homebrewers buy is only food grade, rated to 99.9% purity. That's actually not very pure at all, and there are a lot of other trace gases mixed in with that CO2. Typical oxygen content in food grade CO2 is between 30 and 50 ppm; in other words, force carbonating to 2.5 volumes actually forces oxygen into the beer, on the order of 0.15 ppm or more. For comparison, the most widely accepted commercial bottling standard is under 0.1 ppm and I know that the better brewers like The Alchemist take this very, very seriously.

The hops you used to make your latest IPA have a shelf life of a year or more in the nitrogen purged bags they come in, but I always hear people complaining that their hop forward beers start losing aroma after a month in the keg. Oxygen is the primary driver of beer staling, and force carbonation can be a very significant source of it.

As I posted earlier, most of the scrubbing is going to happen even it you totally carb by spunding. Fermenting 5 gal of 1.040 OG wort to 1.010 FG generates 76 gal of CO2 at STP. That's a little over 15 volumes (76/5.) If you spund to 2.5 volumes of carbonation, you have still vented 12.5 volumes, or 12.5/15 = 83% of the total CO2. You only prevented 17% of the potential scrubbing. The prevented scrubbing is most likely less, as more scubbing will happen early on when the concentration of scrubbed species is highest (unless some of the scrubbed species that you want to retain are created very late in the fermentation process.) For higher OG beers, the amount of vented CO2 and scrubbing will be even higher.

Brew on

 

[Spartan1979]

So, where does one obtain "better than food grade" CO2?

I'll also have to give some thought to adding a carbon filter to my gas lines.

 

[jtp137]

My keged beers have been extremely bitter since I moved wonder if it is c02 to blame since I recently ruled out the water source and cleaned and sanitized all of my equipment

 

[zwiller]

Actually, it does matter. While you're correct that one molecule of CO2 is equivalent to another, there are two caveats you've ignored:

1) Scrubbing of desirable aroma compounds out from the beer like AJ has already described (so I won't go into more detail)

2) Purity of the CO2 source. Believe it or not, most CO2 that homebrewers buy is only food grade, rated to 99.9% purity. That's actually not very pure at all, and there are a lot of other trace gases mixed in with that CO2. Typical oxygen content in food grade CO2 is between 30 and 50 ppm; in other words, force carbonating to 2.5 volumes actually forces oxygen into the beer, on the order of 0.15 ppm or more. For comparison, the most widely accepted commercial bottling standard is under 0.1 ppm and I know that the better brewers like The Alchemist take this very, very seriously.

The hops you used to make your latest IPA have a shelf life of a year or more in the nitrogen purged bags they come in, but I always hear people complaining that their hop forward beers start losing aroma after a month in the keg. Oxygen is the primary driver of beer staling, and force carbonation can be a very significant source of it.

Interesting stuff! My understanding of the basic staling reaction is that o2 interacts with polyphenols (PP) creating metals and stales beer. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjhj7_a0p3NAhXEcT4KHe3XCJsQFggoMAE&url=http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fj.2050-0416.2010.tb00788.x%2Fpdf&usg=AFQjCNHcjSSdO10_-KFdDpP-tB5fOzesUg So if you reduce PP you are at least removing the other variable and mitigating. I have been using polyclar (10m to KO) to great effect preserving quality but there is definitely downward spiral on the dry hop of IPA after carbing. The intro of 02 via force carbing makes perfect sense! YEP; If you research the pro packaging they start talking reducing 02 to ppBillion... Very serious business.

 

[ajdelange]

My understanding of the basic staling reaction is that o2 interacts with polyphenols (PP) creating metals and stales beer.

The transmutation of polyphenols into gold!!!

I think what you meant was that metals catalyze these staling reactions.

 

[zwiller]

Hahaha. Knew I would get busted. Thank you clarifying. I am only dangerous with THAT paper… Was just trying to point out PP play a role in staling and felt a cite was a good idea.

Since I have your attention, mind if I ask you if adding 5g (1tsp) of ascorbic acid at kegging could alter the pH of finished beer?

 

[ajdelange]

Yes, it is an acid as well as a reducing agent. Five grams is 5000/176= 28 mmol and the pK is 4.1 which means that about half (exactly half if the beer pH were 4.1) the protons, 14 mmol, would be available. Beer seems to have a buffering capacity of about 20 mEq/L so you wouldn't have much if a pH shift if you added 5 g to 20 L.

 

[xico]

So am what I taking away from this is that krausening may well be a good option. Every beer I have force carbonated has diminished its complexiity to lesser and greater degrees depending on the brew. Perhaps it's time to go back to keg conditioning.

 

[mabrungard]

Xico, have you been purging your keg by fully filling with sanitizer and then pushing out all the sanitizer with CO2 to assure that there is no oxygen in the keg? In addition, have you performed an airless transfer of your beer from the fermenter to the keg by filling through the beer out post? If not, there is a decent chance that what you are tasting is the oxidation of your force carbonated beers. Is that a possibility?

 

[xico]

Xico, have you been purging your keg by fully filling with sanitizer and then pushing out all the sanitizer with CO2 to assure that there is no oxygen in the keg? In addition, have you performed an airless transfer of your beer from the fermenter to the keg by filling through the beer out post? If not, there is a decent chance that what you are tasting is the oxidation of your force carbonated beers. Is that a possibility?

I recently brewed my 75th batch on my new system I got in October. I switched from bottle/keg conditioning to force carbonation in December and every beer since has been a shade of what I tasted flat, or anything I've made since then. I have had the water tested, I keep meticulous control over pH, maintenance of aseptic environments has been no problem (though I am taking some equipment to the lab tomorrow to see what I've been farming).

Having narrowed the field of possibilities, oxidation is seeming the likely culprit and this conversation has been very informative for me. To answer your questions, yes, I transfer sanitizer from keg to keg and use CO2 head-pressure to daisy-chain the process and push the air out of all the kegs. I use an in-line filter to push CO2 (1 to 2 pounds) into my carboy and use a steel racking cane I bake before transfer into the line-out post on my keg.

I am going to see if I can find an oxygen analyzer that reads to parts per billion and see what my source CO2 reads at.

 

[TheMadKing]

My keged beers have been extremely bitter since I moved wonder if it is c02 to blame since I recently ruled out the water source and cleaned and sanitized all of my equipment

perhaps you've added a little more hops to it

 

[xico]

My keged beers have been extremely bitter since I moved wonder if it is c02 to blame since I recently ruled out the water source and cleaned and sanitized all of my equipment

I'm still on the hunt for a food grade source myself. I would definitely recommend a little filter in-line. My 10 pound steel bottle throws out flecks of rust every so often.

I use CO2 for transfers and purging now but I have gone back to keg conditioning and have had no issues with harsh bitterness, cardboard flavors, muted hop presence. I'm pretty damn sure it's my CO2 source.

jtp137, if you checked your residual alkalinity and bicarbonate levels and you are still coming up with harsh bitterness, it may be worth split batching a few gallons in two kegs and testing force and conditioning methods to see what you get.