I know target cell count, but...

[Saccharomycetaceae]

I know how many yeast cells I want to pitch, but the Mr. Malty Calc has a predetermined pitching rate that is not the same as what I want. Is there a way to figure out, either with Mr. Malty or on my own, how to go about making the starter. I want roughly 313 billion cells (15 million/ml) for a 5.5 gallon batch.

Another thing!
I've heard of doing two-step starters to increase cell count without winding up with a huge amount of liquid to pitch. So, make a starter, let yeast floc out and then use the flocculated yeast to make another starter of the same size...? Is that what people do? Then how do you calculate the cell count of that?
Thanks so much,
matt

 

[MalFet]

The White/Zainascheff yeast book has some growth tables you can use to do the calculations manually. Alternately, Mr. Malty uses 0.75 million cells/mL/ºP, so you can manipulate your gravity reading to give you the cell density you want.

I.e., 15m/.75 = 20ºP, ~= 1.080

 

[Clementine]

The first question on how to make the starter to equal that number of cells, without counting you have to estimate. Maltose Falcon brew club have an article that helped me understand how to guesstimate the yeast cell numbers I had. If you google matlose falcon and yeast propagation and maintenance you will find the link. To summarize the article cell density of a standard OG and nutriented wort is varied only by aeration method. So if you work with a 1040 wort with a correct amounts of nutrient then you can guess how much yeast you have created from their tables.

Doing repeat steps, I think you will run into some problems with this:

1) Most yeast calc tools work off tests where yeast cell count is a related to the volume of the starter and aeration method as started above. So trying to get a yeast calc tool to tell you how much you will have after your second at the same volume step is not going to work.

2) You yeast will get lazy. In yeast propagation you generally step up the starters a set size. Some of the brewing schools teach x5 some teach x10 steps. The size of the step is related not to how much yeast will grow but rather how lazy your yeast will get if the step is too small or how exposed to infection the starter will be if the step is too big. The lazy yeast things comes from yeast behavior. Yeast will first eat the simple sugars, like a two year old at a birthday party, they will eat all the cake and candy they can first. Then when they are done with that they will go and eat the more complex sugars trimaltose etc. If you have too many yeast cells they will eat and multiple on the simple sugars and only a small percentage of the yeast will have an opportunity to eat the more complex sugars (it is only about 10% of the sugars present). So the bulk of your yeast will not have had to adapt to eating the more complex sugars and hence when they are in your wort they will give up after eating the simple sugars having never had to work hard for a dinner.

3) You are probably asking this question not because you don't want to use more wort to make your larger starter but because you don't want to get a larger flask. This next problem is that when you have more yeast eating the same amount of sugar they are going to be extremely active for a short period. Ie have you cleaned your ceiling today? As you have a couple hundred billion yeast cells all eating at once in a relatively small flask.... well you get it.

4) Waste of wort, examples of yeast growth rates where you are pitching a vial into 1L show 150billion increase in numbers where the same vial into a 2L work gives you 200 billion, so better off putting it in a bigger starter.

Hope this helps and I managed to address your questions.

Clem

 

[Sulli]

Give this a try. It's pretty self explanatory. And as accurate as Mr. Malty.

YeastCalc

 

[michaeltrego]

With very fresh liquid yeast and a stirplate, you can grow about 300 billion cells with a 2L starter, which should be close enough to your target. If your parameters are different (older yeast or no stirplate), then Mr. Malty can estimate your results accordingly.

Here is also pitching rate cheatsheet from Northern Brewer that may be helpful.

Assuming you'll need to step up the starter, here is the process that I have used to estimate the resulting cells thanks to Thirsty Boy in Australia:

You can tweak the calculator at Mr Malty to help you work out starter stepping up.

Say you want are brewing a 1.072 bock and you want 500billion cells. That's either a 6L starter on a stirplate, or 5 fresh packs of yeast. But you can step up instead. You are going to pitch a fresh tube/smackpack into 1.0L of wort as your first step.

So what you do, is juggle the gravity and volume numbers in the calculator, till it tells you that you need a 1.01L starter - don't worry about what you are actually brewing, just muck about till it tells you what you need is 1.01L. Now look at the amount of cells it says that will be in that 1.01L starter. Remember that number. (its about 237billion cells)

OK, without changing anything else - go to the % viability input box and increase it. It will go up past 100%. Increase it till the line that says "vials or packs needed without starter" decreases to 1. It will be roughly the amount of cells you have divided by 100billion. so for our example, the percentage figure where the packs needed figure changes from 1.1 to 1.0 is 226% and it says no starter required.

so effectively you have one smackpack with 226% viability.

Go back to the start - plug in the gravity and volume of the beer you want to make - and set the viability to the percentage figure you just worked out (226%) - and now the calculator will tell you what size to make your "second" starter if you use the yeast from the first one. in this example it tells us we need a 2L starter to go from our 237billion cells to 500billion.

So you start with a fresh vial - make a 1L starter - then either decant the beer and add 2L of fresh wort to the yeast, OR assume that all the nutrient is gone, and add a further 1L of double strength wort (which when diluted with the first one = 2L of starter strength wort) - and this will give you the approximately 500billion cells you need. And your starter was never more than 2L.

 

[Saccharomycetaceae]

Awesome,
Thanks a lot. All of that combined is definitely sufficient.