Stepping up

[wbosher]

Hi guys,

I'm about to get serious about using/re-using liquid yeast very soon. I've experimented with harvesting and washing US-05 from the fermenter (thanks Wolfy ) and re-using it, and that was quite successful. My current brew is MJ Burton Union, which I plan to wash and re-use as an experiment also, except this time I will try stepping up using a starter. My last one I just pitched it directly. If this works out I'll take the plunge into liquid yeast.

I'm currently in the process of building a stir plate, just waiting for a few bits and pieces to arrive that I got on ebay, will probably take some time to get here at this time of year, but there's no rush. Plenty of time to absorb all the wise words I will get from this thread.

I have read quite a lot on making starters and stepping up from very small amounts, to eventually get quite a substantial amount of yeast. My question is around the size of the starters in comparison to the amount of viable yeast.

For example, I have seen people stepping up from 200mls, to 500mls, to 2L. Where others start at 400mls, to 1L, to 2L - not exact numbers, just examples to illustrate my point. This will obviously depend on how much yeast you have to start with, but I want to know where these numbers come from, guess work, trial and error, or software?

I've been playing around with this and it seems to be perfect for this sort of work, I just don't quite know how work out the best starter size that will give me good growth, but at the same time not stress the yeast.

The growth factor is obvious, but not so sure about the inoculation rate. It says that it should be between 25 and 100 to keep the yeast healthy and stress free, the that's a pretty huge difference. So do I just try to get a starter size that will roughly double the amount yeast at each step, and at the same time keep the inoculation rate somewhere in this range? Or is there a more accurate way of doing this?

 

[DJ_L3ThAL]

I think from my research the underlying point is that you will never be able to predict your exact starting number of cells anyway so you're starting with a significant margin of error. The best advice I've heard (thanks TSMill) is to just assume a fixed number of cells (if you've got the same vials your harvesting into) of say 1 billion, so step from 200mL to 600mL to 2L which is tripling the volume of starter at each step.

If you chose to make up your own numbers ignoring the tripling bit like 300mL to 900mL to 2L I doubt there would be a large enough difference for you to put your hand on your heart and say there is a difference. My vials have anywhere from 20mL to 40mL of slurry, sometimes I even just tip "a bit" of slurry from a reagent bottle into my flask.

So what I'm getting at is make a solid basis of assumption and just repeat that each time, repeat-ability will allow you to tweak later should you become a professor in yeast B) , enjoy! It's definitely the most fun/sciencey part of brewing!

 

[wbosher]

I've been coming at it from this angle, at least for the first starter before stepping up - Up to one or two week old wash and compacted yeast will have roughly 3 billions cells per ml of yeast slurry. So if I start with 30mls, that will give me a starting amount of viable cells of about 90 billion. Then using the "Liquid Yeast Properties" to work out the viable cell count as time goes on.

As you implied, there is a lot of guesswork, but does this sound like a reasonable approach?