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Measuring Reused Yeast

I’m reusing yeast from a primary fermentation and have separated the yeast from the trub and placed it in 4 mason jars. Most of the yeast have already settled to the bottom. My question is, how do you measure this yeast for repitching? Is there a way to determine the amount of yeast cells based on volume/weight?

When figuring how much yeast to use, it is more important to make sure you have enough than to try and make sure you don’t have too much. In other words, don’t underpitch but don’t worry too much about overpitching. For batches that are the same volume, I’ll pitch about 1/3 the yeast cake from a previous batch into a new batch if they are normal gravity beers, meaning somewhere around 1.050 OG. As the gravity increases, scale it up. For a really big beer, OG=1.090 or higher, I’ll pitch the entire yeast cake.

There are obviously more scientific methods you could use, but this has worked well for me.

[quote=“rebuiltcellars”]When figuring how much yeast to use, it is more important to make sure you have enough than to try and make sure you don’t have too much. In other words, don’t underpitch but don’t worry too much about overpitching. For batches that are the same volume, I’ll pitch about 1/3 the yeast cake from a previous batch into a new batch if they are normal gravity beers, meaning somewhere around 1.050 OG. As the gravity increases, scale it up. For a really big beer, OG=1.090 or higher, I’ll pitch the entire yeast cake.

There are obviously more scientific methods you could use, but this has worked well for me.[/quote]

I’ve harvested yeast from a 5 gallon batch. I plan on making 3 gallon batches from now on, but I’m still not sure how to measure the right amount. I do plan on making a starter before each batch. And I also don’t mind scaling it up. The amount of yeast at the bottom of each of the 4 mason jars I have vary. I could scale up the one with the least amount, but I don’t know how many times I need to scale it up.

Maybe an easier way would be, mix all 4 back together and split it evenly into 2.

I go batch size as my relative scale - I use 1/2 for lagers of the same or similar OG and volume or step up successively by making a small 2.5 gallon batch from a vial or smack pack, then step it up to a 5 gallon, then again to my 10 gallon typical batch size. Stepping down would be proportional, as well, except you also have to factor in the time from harvest. I assume about 15-20% mortality per week, so I don’t reuse really old yeast without making a starter. If making a starter I will use a few tablespoons of the yeast collected. I never rinse the yeast, either, but strain my wort to minimize trub going into the fermenter.

I hope this helps.

:cheers:

Take a look at the White Labs vials to get an idea of what 100 billion cells looks like when it’s densely packed. Then you can shake it up to get an idea of what 100 billion cells looks like when it’s dispersed in ~40mL of wort. If you really want to get a good idea, you can even dump the contents of a fresh White Labs vial directly into a Mason jar and let it settle back out for a few days to see what 100 billion cells look like in that kind of container.

From there it’s all estimation - eyeballing the cake to get a rough idea of how big it is, and estimating what percentage of the cells are still alive based on how long it’s been in the fridge.

Still pretty loosey-goosey, but I’m not sure you can do a whole lot better without breaking out the ol’ hemocytometer.

I’ve dumped some Wyeast 1056 into the same mason jar, without including the nutrient packet, and let that sit in the fridge. The yeast slurry comes out to about 60mL (2 fl oz).

If I were to create a starter with this, does it double the yeast? 100 billion to 200 billion (60mL slurry to 120mL slurry).

Assuming no stir plate, you should be able to get ~200 billion cells out of a 2L starter.

So if I have 30mL of reused yeast, I would need to create a 2L starter twice in order to get ~200 billion cells (30mL → 60mL → 120mL)?

I store my rinsed yeast in a pint jelly jar. I roughly marked the jelly jar in 25 ml increments by using a metric measuring cup.

You can estimate 1 to 2 billion yeast cells per ml depending upon how clean the saved yeast is. I usually estimate low because over pitching is hardly as detrimental as under pitching. Viability of the cells depends upon the fermentation/production date. I use YeastCalc for calculating starter sizes and whether or not a stepped starter would be needed.

http://yeastcalc.com/

30 ml = 30 billion cells. Production date 11/1/2013 = 71% viability = 21.29 billion cells.
1 liter starter, OG 1.037 on a stir plate using Troesters calculations = 161 billion cells.
…intermittent shaking = 82 billion cells

My numbers are rough, but it is what I use. I’m sure there are others with more knowledge in this area.

I store my rinsed yeast in a pint jelly jar. I roughly marked the jelly jar in 25 ml increments by using a metric measuring cup.

You can estimate 1 to 2 billion yeast cells per ml depending upon how clean the saved yeast is. I usually estimate low because over pitching is hardly as detrimental as under pitching. Viability of the cells depends upon the fermentation/production date. I use YeastCalc for calculating starter sizes and whether or not a stepped starter would be needed.

http://yeastcalc.com/

30 ml = 30 billion cells. Production date 11/1/2013 = 71% viability = 21.29 billion cells.
1 liter starter, OG 1.037 on a stir plate using Troesters calculations = 161 billion cells.
…intermittent shaking = 82 billion cells

My numbers are rough, but it is what I use. I’m sure there are others with more knowledge in this area.[/quote]

Thanks! That link is very useful!

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