Acid wash yeast

[Indian]

What is the proper way to acid wash yeast?

[BelgianBrewer]

How to

Let me start by saying that I feel (personal belief) acid washing is a patch for a problem and not a process technique.

There are many washing procedures possible but the most common one is as follows:
- start from chilled slurry
- acidify (phosphoric acid) the slurry to a pH of 2.2 while constantly stirring for 1-2 hours at or below 4 degrees C just prior to pitching
- Sometimes ammonium persulfate is added to increase the effectiveness (0.75%, weight per volume)

Be careful: monitor pH and temperature closely during the acid washing.

Let me know if you need more help.

BelgianBrewer

https://www.sbmbrew.com

[jarviw]

would you elaborate more as why you feel acid wash "is a patch for a problem" instead of a process technique?

there are some studies showing that acid wash actually helps to revive the yeast health...

[BelgianBrewer]

Discussion

There has been a lot of discussion on whether acid washing for yeast is good and helpful.
The principle of an acid wash is based on the fact that yeast cells can withstand a lower pH than most bacteria.
Some bacteria however will survive this process anyway.
Good sanitation and good yeast management should be the basis of your operations, that is what I mean by my comments.

Whether acid washing is good for the yeast cells themselves is not clear either. Lower generation "weak" cells will be killed in the washing process but the vitality level of your yeast in general may decrease as well when acid washing.

My preference is (most of the time) growing yeast from a petri dish culture for every brew and stepping up volume until enough slurry with the appropriate cell count is achieved.

BelgianBrewer

https://www.sbmbrew.com

[jarviw]

thanks for the reply, points well taken!
the yeast quality cannot be improved by acid wash.

I just remember that some claim that acid wash can reduce the lag period, cleans the cell surface, and reduces diacetyl...
but the bottom line is with good, healthy yeast.

[dick murton]

"but the bottom line is with good, healthy yeast." Agreed - there is no substitute fro excellent brewery hygiene. But normally you have to reuse yeast several times. Look under a mike, and you will often not see bacteria because they are so much smaller than yeast cells, and focussing throughout the depth of the fluid between the slide & coverslip is very considerable compared to yeast of bacteria sizes. In other words, with the best will in the world, you are likely to have hidden bacterial contamination. This can lead given the right circumstances, wort, oxygen ntrates / nitrites to bacterial growth and nitrosamine formation. I believe the legal limit for nitrosamines is 30 ppb - easily obtained by a decent bacterial contamination.

So the easiest way out to acid wash as described - but one hour minimum, ideally no more than 4 hours, though I have heard tales of acid washed yeast being held for nearly 24 hours, and still fermenting well.

[pennbrew2]

We're all pros here, no one's going to argue that you shouldn't practice good yeast management. However, as Dick said, bacteria happen.

Acid washing is cheap, easy and effective. The rule of thumb I've always followed is:

pH 2.2 for 2 hours or
pH 2.4 for 4 hours or
pH 2.6 overnight.

"My preference is (most of the time) growing yeast from a petri dish culture for every brew and stepping up volume until enough slurry with the appropriate cell count is achieved. "

Wow, that's a lot of extra work...

---Guy

[jason.koehler]

BB, you must have some very good lab conditions where you work to be able to grow yeast from a dish, and then stepping up to pitchable quantaties...I think the standard brewer would end up growing as much bacteria as they would yeast by doing this!

[BelgianBrewer]

Petri

Stepping up yeast from a petri dish and maintaining petri dish cultures is easy. It is labor intensive, but it is easy.
You do not even need a lab for it, you could do it in a kitchen. Any clean surface that can be sanitized with alcohol can be used.

In the beginning it is also easier to work with two people until you get comfortable.

BelgianBrewer

https://www.sbmbrew.com