Butyric Acid Production in Kettle-Soured Beers

[StaEva]

I've read from several sources that Butyric acid production is cause by anaerobic bacteria. But, the universal method for kettle-souring involves purging with CO2, which would imply that prevention of butyric acid development requires anaerobic conditions. Does anyone know the definitive answer about the metabolic nature of butyric acid bacteria?

[GritCity]

I've read from several sources that Butyric acid production is cause by anaerobic bacteria. But, the universal method for kettle-souring involves purging with CO2, which would imply that prevention of butyric acid development requires anaerobic conditions. Does anyone know the definitive answer about the metabolic nature of butyric acid bacteria?

I am also curious to find any research results on butyric acid production. I have read that temperature can also inhibit or promote production. I was told to keep kettle souring temps as high as possible to limit butyric acid but I haven't found any source material and definitive temp recommendations. I've also read (I think in American Sour Beers) that Brett can convert it to ethyl butyrate (pineapple) over time.

Would love to see what anyone else has on this.

[bwalden234]

Chad Yakobson...

I don't know if you listen to the brewing network (or how prevalent it is in the pro world for that matter), but they did an interview with Crooked Stave's Chad Yakobson (sp). He did his thesis work on brett and wild fermentation. He did say that brett could break down butyric acid at low levels but that it took a long time. He also made the point that good process control was needed to make good kettle soured beer. Starting with wort at the 3.9 - 4.4 ish range (hazy on the numbers) was important to inhibition of non lacto-producing bacterial growth. I am, admittedly, new to making sours and it is not something we will tackle right away at our brewery, but I enjoy making them and have been doing my research. Here is what I founds so far:

The Brewing Network:
Crooked Stave episode 04-15-2012
The Sour Hour - All episodes

Other Stuff:

http://www.milkthefunk.com/wiki/Main_Page

http://www.themadfermentationist.com/

http://www.brettanomycesproject.com/dissertation/

and of course here at probrewer.

Hope this helps, I still have so much to learn about sours....

[StaEva]

Grains...

I should specify that I'm specifically referring to the use of crushed grain as an inoculation source in the kettle. I dislike the predictable and uni-dimensional character of pure-culture kettle soured beer.

As for the above response RE pH, I've heard from a VERY reputable brewery that pre-soured wort pH is not relevant in their process and that they only control temperature, ambient gas, and quantity of grain used for inoculation. Pre-soured wort pH of up to 5.6 has yielded very positive results for this brewery, and again, their reputation for quality is unassailable.

[tjc27]

So you have two major things to look out for, Isovaleric and Butyric acid. Butyric is anaerobic just as lactobacillus. The key to prevent Butyric is to lower the wort ph to around 4.5 prior to inoculation. When the wort is below 4.7 to 5.0 clostridium (the produce of Butyric) is inactivated and will not produce the vomit smelling acid. Isovaleric is aerobic and therefore purging the wort with c02 will aid the prevention of the dirty feet smell/flavor.

That being said I would suggest a starter, you can inoculate a small sample size with grains and taste it prior to pitching to ensure you will like it. Take a sample size of wort, purge with co2, lower PH to 4.5 with lactic acid, and keep at a warm temp (90 to 115) for 2-3 days. Then taste it and check PH, if it tastes good and the PH is in the mid 3s you can grow it up from there. There is less chance of losing a large batch this way.

[bwalden234]

The three times I have done Berliner's I have used the "handful of grain" method. The one that went bad was a process issue where I didn't bubble enough co2 through it. Lacking a PH meter at the time it was def luck of the draw. I agree with making multiple starts and using the one that smells/tastes the best. We have two breweries in my are that make Berliners and the one that uses a naturally started culture has a much better range of flavor than the one purported to use a bought culture.


Bill Walden
Oddball Brewing Co.
Suncook, NH

[tjc27]

There are other sources too you can try yogurt, probiotics, Good Belly drinks, etc. The Commons Brewery uses yogurt last I heard and they won a Silver at GABF. But yeah i agree, one strain of Lacto from a lab is a little one dimensional.

[StaEva]

Perfect.

So you have two major things to look out for, Isovaleric and Butyric acid. Butyric is anaerobic just as lactobacillus. The key to prevent Butyric is to lower the wort ph to around 4.5 prior to inoculation. When the wort is below 4.7 to 5.0 clostridium (the produce of Butyric) is inactivated and will not produce the vomit smelling acid. Isovaleric is aerobic and therefore purging the wort with c02 will aid the prevention of the dirty feet smell/flavor.

That being said I would suggest a starter, you can inoculate a small sample size with grains and taste it prior to pitching to ensure you will like it. Take a sample size of wort, purge with co2, lower PH to 4.5 with lactic acid, and keep at a warm temp (90 to 115) for 2-3 days. Then taste it and check PH, if it tastes good and the PH is in the mid 3s you can grow it up from there. There is less chance of losing a large batch this way.

Exactly the information I was looking for. Thank you.

[StaEva]

Yogurt

There are other sources too you can try yogurt, probiotics, Good Belly drinks, etc. The Commons Brewery uses yogurt last I heard and they won a Silver at GABF. But yeah i agree, one strain of Lacto from a lab is a little one dimensional.

Yeah, we've used yogurt a few times with reliably decent results, but I again feel it's too one dimensional even with the two orthree strains of Lactobacter most yogurts use. I've just never had anything that compares to the depth of grain-souring.

[bwalden234]

An interesting idea....

Would be to make starters with different grains and see what the differences are. hmm may have to set this up once we paint the brewery.