Yeast Acid Washing: How To Neutralise the Acid?

[Protos]

I'm readying to acid wash my yeast for the first time. I have fresh starter slurry of a rare Kveik yeast, stored frozen for a year in Glycerol, and now successfully unfrozen and propagated. It has slight Lactic (I assume) infection which I want to get rid of. The batch I harvested it from was a bad one (slight Lacto infection and underattenuation). I can't buy this yeast fresh anymore, that's why I harvested and froze it even knowing it's bad, and now I need to salvage it.
I have no Phosphoric acid so I will be using Citric, keeping my slurry chilled at pH2.2 for an hour.
The first batch to brew with this yeast will be a very small one, 4L / 1G, just to propagate more yeast for the "real" high-gravity batch.
I experimented beforehand with making Citric acid solution. It's so acidic, I'm afraid of adding this into such a tiny batch, even 50 ml of Acidified slurry of pH2.2 will sour the beer more than any Lacto infection would have otherwise.

My question is, is there such a thing as neutralizung Acid Washed Yeast before pitching it? How do you do it? I think, I will use Slaked Lime solution for neutralizung the acid.

 

[jpitz31]

All of the videos I have seen on acid washing is you add the acid to your pitching yeast within 30 minutes, ( ph level determines how long you can wait before pitching) Once at the proper ph level you pitch the yeast with the acid in the culture. Go to Youtube and search for acid washing yeast. In the video he used phosphoric acid to wash the yeast.

 

[madscientist451]

Good luck with that....
If you want to try to solve yeast problems by "washing" it, go for it....
Sorry if I sound skeptical, but I really am hoping it works out.

 

[IslandLizard]

I always wanted to try, but never acid washed yeast, because I was under the impression Chlorine Dioxide was the acid of choice, which can be hard to obtain.
After some Googling, Phosphoric or Citric Acid seem to be very acceptable alternatives, while a (serious) homebrewer may already have ample amounts of those on the shelf.

I also did a search in this (yeast) forum for threads on acid washing. There's only one thread that goes into it at some depth:
https://www.homebrewtalk.com/threads/yeast-washing-with-citric-acid.221161/

 

[Protos]

Thanks guys, useful tips, I think I have a general idea on yeast washing process. I have the "Yeast" book too, there's a short manual by Chris White in it.

The only thing I'm still confused about is neutralizing acid before adding the acidified slurry to the wort.
Nobody but a single post on a different homebrew forum seems to mention that. And I think neutralizing is necessary, as addind a pH2.2 slurry into a small batch looks like a certain way to screw the acidity balance of the beer

 

[Protos]

Good luck with that....
If you want to try to solve yeast problems by "washing" it, go for it....
Sorry if I sound skeptical, but I really am hoping it works out.

I have no high expectations regarding this case. I just have no options left other than acid wash. Infected yeast, no way to resupply it fresh, very good strain that's pity to discard...
Otherwise I wouldn't do it.

 

[mendelec]

Personally, if I were in your situation, I'd get some agar and some sterile petri dishes off Amazon or elsewhere, make up some agar plates, and streak that sucker out or do serial dilutions until you have individual colonies. Pick out a yeast colony. Repeat one or two times. Then, you know it's clean. But, I have a microbiology background. Might not be for everyone. It's no harder than making frozen stocks though.

Heck, if the strain is fascinating enough, I'll bet you could find someone willing to help you do it.

 

[IslandLizard]

Personally, if I were in your situation, I'd get some agar and some sterile petri dishes off Amazon or elsewhere, make up some agar plates, and streak that sucker out or do serial dilutions until you have individual colonies. Pick out a yeast colony. Repeat one or two times. Then, you know it's clean. But, I have a microbiology background. Might not be for everyone. It's no harder than making frozen stocks though.

Heck, if the strain is fascinating enough, I'll bet you could find someone willing to help you do it.

I totally agree, it's the only way to isolate that yeast strain. But it also takes about a month to build it up and get a new pitch ready and freeze the rest.

So, maybe wash some and see where it leads, and keep some behind (before washing) for plating to isolate and rebuild?

Is buying ready made agar dishes the way things are done now? No-one prepares them anymore from powder?

 

[mendelec]

I make my own from agar powder and DME. I keep a sterile bottle of agar in dme on hand (pressure cooker as an autoclave) to microvave to melt and pour on short notice. Much like my old lab days. If I'm unsure of the sterility of my petri dishes, I'll sanitize them before use. My workspace is nowhere as clean as I'd have kept my old lab bench, but I've never had an issue (not that I plate things all that often). Easy peasy.

Never had an infected batch or culture, but I'll plate things out when I'm trying to isolate a yeast from a beer I particularly like. (I've developed the habit of traveling with a few sterile conical centrifuge tubes just in case I encounter something while traveling that inspires or intrigues me. Goes in with my little bag of 3oz or less carry on liquids and then I'll plate it out when I'm home.)

 

[Protos]

Well, I've just brewed my mini batch and added my acid-washed starter "as is", no neutralizing (because, beforehand, I made and tasted 2 samples of exactly same amount of acid which I washed my yeast with, neutralized one with Baking Soda and another with Slaked Lime, pH pushed to 5.0, both tasted disgusting).

Got post-inoculation wort pH of 4.01 (I purposely brewed an alkaline wort, post-boil pH 6.62, hoping the starter won't acidify it too much) and it's barely drinkable now, worse than the worst Lactic infection I've had.

Anyway, even if the batch is screwed, I'll have plenty yeast from it, which may be good - and if not good, may be plated. Never tried plating yeast, why not to acquire a new skill.

 

[Elysium82]

Personally, if I were in your situation, I'd get some agar and some sterile petri dishes off Amazon or elsewhere, make up some agar plates, and streak that sucker out or do serial dilutions until you have individual colonies. Pick out a yeast colony. Repeat one or two times. Then, you know it's clean. But, I have a microbiology background. Might not be for everyone. It's no harder than making frozen stocks though.

Heck, if the strain is fascinating enough, I'll bet you could find someone willing to help you do it.

Hi. Sorry for slightly hijacking this post. So, you just get the healthy yeast of the petri dishes and make the starter out of that? Are there any videos on this practice?
UPDATE: This website is deadly:
https://braukaiser.com/wiki/index.php/Growing_Yeast_from_a_Platehttps://braukaiser.com/wiki/index.php/Inoculating_Plates_and_Slants

 

[Hunny Bunny]

Is it out of the question to add sulfites to reduce undesirable bacterial strains? I had heard of this before, and a quick search showed me this on the internet, because I have had massive invasions of lactobacters and acetobacters in the past turning my wort into kombucha and other nasty stuff before... Sulfites Are Your Friends - Keystone Homebrew Supply

 

[Protos]

Well, I've just brewed my mini batch and added my acid-washed starter "as is", no neutralizing (because, beforehand, I made and tasted 2 samples of exactly same amount of acid which I washed my yeast with, neutralized one with Baking Soda and another with Slaked Lime, pH pushed to 5.0, both tasted disgusting).

Got post-inoculation wort pH of 4.01 (I purposely brewed an alkaline wort, post-boil pH 6.62, hoping the starter won't acidify it too much) and it's barely drinkable now, worse than the worst Lactic infection I've had.

Anyway, even if the batch is screwed, I'll have plenty yeast from it, which may be good - and if not good, may be plated. Never tried plating yeast, why not to acquire a new skill.

A follow-up!
The batch was screwed indeed. But it was a mini-batch anyway, essentially a large starter. I've already used the propagated yeast in several new batches which I'm very happy with. No acid. The yeast is clean and perfect now, it's been successfully washed and multiplied, a part of the clean slurry is Glycerine-frozen and I'm very satisfied.
So I've learned that the most certain way to neutralize the acid-washed yeast is to propagate it one more step.

 

[whattabrau]

How much acid did you use? I recently tried washing -- between your first and currently last post in this thread -- and it took only about 1mL of 75% phosphoric acid to bring the ~2dL of thin slurry pH down to 2.14 (~8degC). I probably could've added a few drops more, but since it was my first time acid washing, I was trying to err on the side of keeping the yeast alive. After an hour on the stirplate in the fridge, I pitched the acid wash into a 1L starter made with half wort borrowed from the mash half tap water and 0.5g of chalk, and after some minutes on the stirplate measured the pH of the starter to be 4.54 (~21degC). Granted, the tap water here is decidedly alkaline. At any rate, 1mL of phosphoric acid is about the equivalent what I add to the kettle anyway for 5gal, so skipping the starter it should just cancel out without extra water or chalk (minus benefits from dropping the kettle pH to around 5.2).

In any case, I'm now wondering why acid washing is seen as such a bother. It takes just a few minutes, uses things that I already have out on brewday, and at least based on a fermentor sample improved my "hobby yeast" that's been repitched about 20 times. I didn't see any poor fermentation kinetics either, and fermentation took off like a rocket in some hours -- the starter was already going strong by the time I pitched it.

I do regret not thinking about measuring the slurry pH after the hour on the stirplate, so as to know if I should indeed add those extra drops of acid next time. pH 2.14 at 8degC might be too high if the slurry managed to chill to 3-4degC in the hour (didn't measure the post-spin temperature either).