yeastcalc.com question

[dermotstratton]

I just recently started making yeast starters. I have a 2L flask and a stir plate. I have been checking out the yeastcalc.com website and have a few quick questions if someone could help me out. I attached a screen shot of what I calculated from website.

Am I right in assuming to create starter per these instructions, I would need to buy 3 vials/smack paks of yeast and put them all in a 2 liter starter, put it on a stir plate and let it ferment for 24 hours. Then I would cold crash starter, decant off wort to leave behind only a yeast slurry. I would then add 2 more liters of wort to this yeast slurry, let it sit on the stir plate for 24 hours again. After that, I should have 804 billion cells (more than enough for my beer).

My questions are:

1. Is there a maximum ratio of yeast to wort that is acceptable in 1st step. (i.e. can I put 4 vials of yeast in a 1 Liter starter or will that "suffocate" the yeast and not allow it to grow?)

2. I have read that when stepping up yeast, you should aim for the second step to be 10X the first step. I only have a 2L flask, so am I causing a problem by making the 1st step and the 2nd step the same volume? (Not sure if the 10X step is assuming you do not decant wort off of yeast after first step).

Looking forward to figuring out the mechanisms behind yeast starters and stepups. . .

 

[Sulli]

Your Erlenmeyer is way too small for what you're trying to do. If you go and dump 3 vials of yeast into a 2 liter flask that is filled to the 2 liter mark you're going to have a volcano on your hands.

You would be better off making a 1 gallon starter and pitching your 3 vials into that, and even then you might have some blow-off.

 

[dermotstratton]

Thanks for your feedback. What do you think the maximum amount of vials you can pitch into a 2 Liter Erlenmeyer? To date, I have only done 1 vial into 1.5L of wort as that has been more than enough cells for the low to moderate gravity ales I normally brew. I suppose I could invest in a larger Erlenmeyer.

I am still interested in getting an answer to my two questions if anyone knows the answers. Specifically about the "stepping" up theory. When stepping up, is it best to cold crash, decant and repitch with new wort? or if container space is not an issue, is it best to throw new wort into for second step without decanting? I suppose I should probably try and get a copy of JZ's new yeast book?

 

[Sulli]

My questions are:

1. Is there a maximum ratio of yeast to wort that is acceptable in 1st step. (i.e. can I put 4 vials of yeast in a 1 Liter starter or will that "suffocate" the yeast and not allow it to grow?)

2. I have read that when stepping up yeast, you should aim for the second step to be 10X the first step. I only have a 2L flask, so am I causing a problem by making the 1st step and the 2nd step the same volume? (Not sure if the 10X step is assuming you do not decant wort off of yeast after first step).

Looking forward to figuring out the mechanisms behind yeast starters and stepups. . .

1. Adding more than 2 vials to a 1 liter starter is counterproductive.
Example: If you add 1 vial to a 1 liter starter your going to produce about ~128 billion new cells.
Add 2 vials to a 1 liter starter and you'll produce around ~134 billion new cells.
3 vials in a 1 liter starter will only produce about ~118 billion new cells.
4 vials in 1 liter = ~90 billion new cells.
You can see where this is going.
You would be better off adding just 2 vials to your 1 liter starter and then adding the other 2 vials to the fermenter when you pitch.
The reason the amount of new growth keeps declining is because as the inoculation rate of the starter increases the amount of food for the yeast colony decreases.
(Edit: I should add that these numbers are for stirplate propagations.)


2. The 10x step up ratio is more for pro brewers who are propagating yeast starting with very small amounts; it's recommended that they don't exceed 10x, but it doesn't hurt to step at a smaller ratio. In fact the Germans advocate not exceeding a 5x step up.
For the average homebrewer the 10x step ratio is impractical and unnecessary.
You're not hurting your yeast by stepping with the same volume, but you're not maximizing your efficiency either. If you have the means to increase the second and third step by about 2x each, you will get far more bang for your buck.

Hope this helps.

 

[dermotstratton]

Definitely makes sense. I'm guessing that there must be an optimal ratio of yeast volume to wort volume. I'll play around with the calculator and figure that out. In general, though, diminishing returns as you add more vials to the ame volume of wort.

I still don't quite understand though if it is better or worse to decant wort from 1st step and then pour new wort in its place.

For example:

If I make a 1 liter starter with 1 vial, I'll end up with 228 total cells (per your calculation above) in my flask in ~1.1 L of liquid (1L wort + .1L from White Labs yeast tube). At this point, I have two options:

1. Allow starter to settle and decant off ~ 900-1000 mL of work, leaving behind 100-200 mL liquid. Next add 1.5L-2L of fresh wort to this yeast slurry, but it back on stir plate and let second step finish.

2. Just put another 1.5-2L of fresh wort into complete fermented 1.1L solution to end up with 2.6L - 3.1L of liquid in flask (this of course assumes I have a big enough starting flask to do this), but it back on stir plate and let second step finish.

Should these two options result in the same outcome?

 

[Sulli]

I would think that they would result in the same outcome.

IMO, If you have a large enough flask, Option 2 would be better.
The spent wort isn't going to hurt anything and you shave an entire day off the stepping process.
Your definitely going to want to decant before you pitch that into your beer though.

 

[dermotstratton]

Cool, that's what my logic was as well, but wanted to see what others thought. Thank you for all your input. I think I can make life easier on myself by buying a 5L flask.

 

[nealperkins]

And...buy yourself some anti-foam! Which, by the way...for some reason I do not understand at all...seems to have a life span, a pretty short one. You'll soon have the regrettable experience of the 'volcano' referenced earlier. (And, when you went to bed it looked so tame...) Note: my experiences are with stir plates and constant aeration.

IMHO, 2L equals 1 vial, unless, you've got other time issues not allowing a step up. But, there are lots of good experiences/knowledge in this thread.

 

[Sulli]

+1 on the anti-foaming agent (i.e. stress reducer).