Yeast Rinsing 101

[Klickitat Jim]

Why not just store your yeast on the beer that it made, and instead of trying to rinse wash flush the hop matter away, just use a small amount and grow up a starter?

[NateBrews]

Well, I'm not really storing it for any amount of time (maybe a day). I'm not passing on the hop matter and junk that got into the fermentor, I'm more concerned with the alpha acids that on the yeast themselves. One of the big reasons to repitch the slurry is so that I don't have to grow a starter when I already have 500mL of thick yeast slurry from a batch that just finished. For bigger lagers, this is particularly true since the starter needs to be huge and that starter might as well be a low gravity batch of something.

[Klickitat Jim]

I may be wrong, but I doubt that water removes much hop oil. I think rinsing is ok if the rinsed yeast aren't stored on the rinsing water for too long. I tried rinsing for about a year using jamils method mentioned on brew strong. It didnt hurt my final product but it didnt really improve it either. If I repitch now, I use about 100ml and make a starter. For me the best beers are fresh cultures in a starter, then the starter from 100ml slurry, beyond that its a wash. I also found, I think, that I had a tendency to grossly over pitch when I was direct repitching slurry.

[brewinhard]

I also found, I think, that I had a tendency to grossly over pitch when I was direct repitching slurry.

That is pretty easily done as it is kind of hard to estimate the thickness of the slurry. When I repitch from a prior fermentation, I leave a bit of beer on the top of the yeast cake and gently swirl it up into suspension. I then let it sit for few minutes to allow the heavier solids to drop out. Then I pour enough yeast (according to Mr. Malty and my OG) into a sanitized graduated mason jar. I then let it sit overnight in the fridge and let it condense to hopefully the amount of yeast I need (give or take a bit) for my brew the next day. It still is not an exact science (at least for me).

[Klickitat Jim]

I also found, I think, that I had a tendency to grossly over pitch when I was direct repitching slurry.

That is pretty easily done as it is kind of hard to estimate the thickness of the slurry. When I repitch from a prior fermentation, I leave a bit of beer on the top of the yeast cake and gently swirl it up into suspension. I then let it sit for few minutes to allow the heavier solids to drop out. Then I pour enough yeast (according to Mr. Malty and my OG) into a sanitized graduated mason jar. I then let it sit overnight in the fridge and let it condense to hopefully the amount of yeast I need (give or take a bit) for my brew the next day. It still is not an exact science (at least for me).

Similar to what I would do. It seems like a lot of WLP vials that have sat a while are half heast ish. So my direct repitch method is to leave an equal depth of beer on top of the yeast cake in the fermenter, swirl and pour into a 2 qt jar. If I am using direct repitch its normally brewed and pitched within 24 hrs of racking the previous beer. Then when its time to pitch I shake it so its a homogenous slurry, usually pretty thin like what comes out of a wyeast pack, and I figure 1bill per ml. So a standard lager probably gets 300 ml and a standard lager gets about 5-600 ml. If im doing a starter I do tge same think but the starter gets about 100ml. I do 2L starters by the way, on 1.030 precanned wort with wyeast nutrients, oxygenated huge. And the yeast is always in a proper pH liquid that it created itself rather than 7 pH distilled water.

[S. cerevisiae]

I have been preaching for quite some time that rinsing yeast with and storing it under boiled water is not a biologically sound practice, especially when executed by someone without laboratory experience. Yeast cells do not need to be kept physically clean as much as they need to be kept biologically clean. Boiled water is not truly sterile. It's more like hypersanitary. Vegetative cells are killed by the time that the temperature of a liquid reaches 70C/158F; however, the temperature of a liquid must be raised 40 degrees Celsius above 70C in order to denature spores. The generally accepted laboratory practice for rendering a liquid sterile is by processing it at 121C/250F at 15 pounds per square inch above normal atmospheric pressure (approximately two Earth atmospheres of pressure) for 15 minutes. Water does not boil until 121C/250F is reached at 15 pounds per square inch above normal atmospheric pressure. There is a way to render water sterile via boiling called Tyndallization, but the liquid must be boiled on three consecutive days. Tyndallization works by killing vegetative cells, allowing spores to germinate, and then killing the germinated spores.

With that said, here is something that I posted on another forum:

A yeast culture "owns" a batch of wort by shutting out competitors. It rapidly consumes dissolved oxygen, which shuts out aerobic microorganisms. A yeast culture also lowers the pH of the medium from around 5.2 to around 4.2, which shuts out pH sensitive anaerobic microflora. The final defense that a yeast culture mounts is the production of ethanol, which is toxic to microorganisms, including the culture itself.

Replacing green beer with boiled water strips the culture of the force field that it built for itself, which means that the water has to be completely free of wild vegetative cells (and spores that can germinate into vegetative cells) because they will feast on dead yeast cells. Bacteria cells multiply three times faster than yeast cells (i.e, an eight-fold increase in bacteria cell count for every two-fold increase in the yeast cell count), which means that a small infection can overtake a larger yeast culture when pitched into fresh wort.

The best way to crop is to "top crop" at high krausen. However, top-cropping requires one to use a true top-cropping strain in order to be most effective. Top-cropping naturally purifies a culture because wild yeast and bacteria do not floc to the top. Top-cropped yeast can be repitched almost indefinitely.

When using a non-top-cropping yeast strain, I usually leave enough liquid behind after racking to be able to swirl the solids back into suspension (my primary volume is 1/3 to 1/2 gallon larger than the volume I expect to rack). Swirling the solids back into solution using green beer, waiting a few minutes for the heaviest fraction to settle, and then decanting the liquid fraction has the same effect as rinsing with boiled water; however, it keeps the low pH, ethanol laden environment intact. If one wants to attempt to rid the culture of mutants, one can decant and discard most of the supernatant (liquid above the solids) as soon as a creamy layer of yeast forms on the bottom of the container.

As stated above, one of the first things that a yeast culture does when pitched into a batch of wort is to lower the pH from around 5.2 to around 4.2. One has heard that pathogens do not grow in beer. One of the reasons why pathogens do not grow in beer is due to its relatively low pH. For example, Clostridium botulin growth is inhibited below pH 4.6.

Contrary to what was written in early amateur brewing books, brewing yeast cultures do not respire in wort due to a phenomenon known as the Crabtree effect. Hence, brewing yeasts do not go through a period of respirative (aerobic) growth before they start to reproduce fermentatively (anaerobic growth). In the presence of glucose levels above the Crabtree threshold, all reproduction is fermentative. As many of you probably noticed while reading Yeast, yeast cells use dissolved oxygen to build ergosterol and unsaturated fatty acid (UFA) reserves (these reserves are shared with with all of the daughter cells). Yeast cells perform this feat by shunting oxygen to the respirative metabolic pathway while simultaneously metabolizing the carbon source via the fermentative metabolic pathway.

What this preference to reproduce fermentatively means to a brewer is that yeast cells pretty much start producing ethanol almost as soon as they are pitched into a batch of wort. While ethanol has a limiting effect on the viability of a yeast culture, it also protects the culture from infection. Boiled water is not truly sterile. Boiled tap water also tends to have a pH of at least 7.0; therefore, it raises the pH of the culture.

With the above said, most experienced amateur brewers eventually reach the conclusion that one can just crop and repitch without doing anything to separate the viable cells from the dead cells and break material, especially if they leave most of the break and hop material in the kettle. Less is definitely more when cropping yeast.

[BDawg]

Great info. Thanks for sharing.

[dogismycopilot]

Great info. Thanks for sharing.

Agreed. Glad you joined the ranks, Sacc.