Raw ale/no boil and kettle souring: two chemistry questions

[tiredofbuyingbeer]

I'm going to try to make a kettle soured, no boil gose. Basically, I'm going to sour the wort with a big lacto starter, then I'm going to raise the temperature to about 160F for 30 minutes in order to pasteurize and to add hops.

Two questions:

1. How much water do I need to collect for a 5.5 gallon batch? Normally, I collect about 7-7.5 gallons to account for evaporation. But I have no idea how much evaporation to expect from work kept at 160F for 30 minutes.

2. How does boiling affect pH, and how would that affect my final beer? My target pH for the kettle sour is 3.5. Naively, I would have thought that boiling would "concentrate" whatever makes a solution sour. Like, if you reduced vinegar, it would be twice as sour. I'm pretty sure that's not, in fact, true, though. If I started with 3.5 pH wort and boiled for 60 minutes, would I end up with roughly a 3.5 pH wort, or would it be more sour? Or less sour? An answer to this question could help me decide how sour to make the beer given that I don't plan on boiling.

 

[TheMadKing]

So I would assume almost 0 evaporation at 160F, especially if you leave the lid on.

If you're adding hops there isn't a great way to calculate hop utilization sub boiling. Maybe set beersmith to whirlpool hops only and that should get you close ish.

Boiling or heating will have minimal effect on the pH so no worries there. The only thing you should keep in mind is that yeast doesn't work well below about 3.4, so I wouldn't go any more sour than that.

 

[RPh_Guy]

I have read that boiling does reduce the pH marginally. However pH is logarithmic, so the decrease is certainly not proportional to volume reduction.
Also, sourness is perceived by "titratable acidity", not pH, so while the pH may not change much, the acid and its salts will increase in concentration during a boil and so it will taste more sour.

My question for you: Why are you not boiling? Boiling both before and after the souring is the usual process for a kettle sour. Wild bacteria may survive the mash and cause off-flavors during the souring process.

The only thing you should keep in mind is that yeast doesn't work well below about 3.4, so I wouldn't go any more sour than that.

This goes against what I've read and have seen from others here and from my own limited experience. Any yeast should be fine at low pH, just a little more sluggish.

Cheers

 

[TheMadKing]

I have read that boiling does reduce the pH marginally. However pH is logarithmic, so the decrease is certainly not proportional to volume reduction.

Also, sourness is perceived by "titratable acidity", not pH, so while the pH may not change much, the acid and its salts will increase in concentration during a boil and so it will taste more sour.



My question for you: Why are you not boiling? Boiling both before and after the souring is the usual process for a kettle sour. Wild bacteria may survive the mash and cause off-flavors during the souring process.





This goes against what I've read and have seen from others here and from my own limited experience. Any yeast should be fine at low pH, just a little more sluggish.



Cheers

Well unless you're planning to measure the TA, pH is the more convenient measurement to use to gauge sourness, but yes you're technically correct.

I also said "minimal effect". Your soured beer will taste pretty much the same after boiling as it did before boiling, and I challenge you to prove me wrong in a blind taste test. But again, you're technically correct that boiling can affect the TA.

Yeast will certainly work below 3.4, yes, but they will not work WELL meaning you will probably not reach the same terminal gravity with a pH of 3 vs a pH of 3.4. So again you're technically correct that yeast will work below 3.4

If you want to talk semantics I'm happy to, but in terms of actual effect on the finished beer that will result in a significant difference in perception? I think you'll find everything I said to be accurate and result in a better beer for the OP.

 

[RPh_Guy]

The wort would be too sweet to detect a difference pre- & post-boil. (So yes you are technically correct ). However I feel confident arguing that a higher concentration of acid results in more perceived sourness (in the final beer).

As far as having a lower attenuation, you might be right. The kettle sour I fermented with US-05 at pH 2.28 didn't attenuate as much as it would have normally. Maybe some yeast nutrient might have helped. It's just that everything else I've read from people with more experience says that the yeast will be fine. Maybe they have lowered expectations with regard to attenuation. I could dig around for some references if you think I'm crazy or are otherwise curious.
Mine was throwing off some amazing bubblegum and clove esters during fermentation but these didn't show in the final beer (unfortunately?).

 

[RPh_Guy]

Obligatory meme:

https://goo.gl/images/Wg3FLM

 

[radwizard]

I get good attenuation in my kettle sours by souring a portion of my starter and letting yeast adjust to that before pitching . Certain yeast strains are happier in the acidic envirnment as well. You really cannot go wrong with Sac Trois,

If I am going to boil post souring, it is usually to kill the LAB, and add hops and spices. If I am going to add brett I prefer to keep everything alive...

That I know of, I never gained or lost acidity after boiling, but I have not really boiled long and hard enough to have substantial evaporation loss. I usually only do a 20 min. boil post souring.

Are you planning on adding lactic acids before pitching you microbes??

 

[tiredofbuyingbeer]

Thanks for all of the feedback, everyone.

RPh Guy, the reason I'm not boiling is because I think it might make a lighter beer, but mainly because I want to try a technique I haven't tried before. My thought was that if I mash-out at over 160F for 10 or 20 minutes, my wort will be pasteurized, and if I have a long and high-ish sub-boiling hop stand after souring, I'll have a low degree of bacteria in the wort before I ferment. Do you think that won't be the case?

As far as yeast go, I was just going to try to hit 3.5, which I think is reasonable for a gose, then pitch 2 packs of K-97 and hope for the best.

 

[RPh_Guy]

RPh Guy, the reason I'm not boiling is because I think it might make a lighter beer, but mainly because I want to try a technique I haven't tried before. My thought was that if I mash-out at over 160F for 10 or 20 minutes, my wort will be pasteurized, and if I have a long and high-ish sub-boiling hop stand after souring, I'll have a low degree of bacteria in the wort before I ferment. Do you think that won't be the case?

"Pasteurization" doesn't necessarily kill all the microbes, so if you are at all worried about exposing your cold-side equipment to wild bugs you won't want to skip the boil. It might be fine but it is more risky.

Besides sterilization and activation of hop oils, boiling concentrates, stops enzymatic activity (thus increasing head and body), removes large proteins (thus preventing chill haze), and removes sulfur compounds (DMS). These functions aren't strictly necessary for a low-IBU beer, so experiment away!

Cheers

 

[radwizard]

So you are Mashing, Pasteurizing, Souring, and then Pasteurizing again (adding IBUs in a hop stand). That should work fine. It is good practice to add acid before your sour culture as well. If you are souring with LAB, pasteurization after the souring is complete, should kill it. You can over pitch brewers yeast and/or add acidity to the starter to improve the yeasts preformance.