Yeast volumes?

Quick one here...If I am making a 2L starter in a 1L flask, using the decanting method can I ferment 1L then decant and add 1L and finish. Decant and pitch. That would still make it a 2L starter correct.

My thought is I'm pouring off fermented wort not yeast so by the end of the starter I would have as much yeast as if I did a full 2L starter correct?

According to my biology education... not necessarily.*

The problem is that yeast grow on a sigmoid (s-shaped) curve. Growth/multiplication is slow at first, picks up to a maximal rate, and then levels off... which is where your starter is when you decant.

AFAIK, adding more nutrient is not enough to put them back into the steep part of the curve. You would be better off decanting, then putting 90% of the yeast in a sanitized jar, leaving them in the fridge for a day or so, and then making an entirely new starter with the second liter of culture liquid and 10% of the starter yeast. That way you end up with the 1L of yeast in the fridge and the 1L of yeast in the starter, so you can pitch both on brew day.

Warm the refrigerated yeast up before pitching, and if you want to "wake" them, add a bit of boiled and cooled malt about 20 minutes before you pitch them.

I have never done this myself, preferring to work with dry yeast whenever possible, but according to my training in laboratories, that's how I would go about it, given your equipment and your goals.

*I am not a yeast biologist.

How would a stir plate effect this. I'm not a biologist at all but isn't a stir plate to keep yeast in suspension, therefor could you run the stirplate. Then chil decant add more wort and stirplate again? Would the movement of contestant during and additional o2 wake them back up?

Stirplates allow microbes to have planktonic growth instead of sessile growth. The colony can be bigger, and you should use a stirplate if you have one, but if you use it for the 1st liter you will already have the benefit of it and it therefore can't get the 2nd liter even larger.

You can think of the stirplate as kind of like watering your lawn. Your lawn grows better if it is watered, but it doesn't grow to cover twice as much ground.

Seriously, just sanitize a jar with your liquid sanitizer, pour your first batch of yeast in there, put it in the fridge for a day or two while your second starter grows up, and then pitch them both on brew day. It's not complicated.

The fridge won't hurt your yeast over a short period of time... where do you think the homebrew store keeps their yeast?

jtupper said:

How would a stir plate effect this. I'm not a biologist at all but isn't a stir plate to keep yeast in suspension, therefor could you run the stirplate. Then chil decant add more wort and stirplate again? Would the movement of contestant during and additional o2 wake them back up?

Click to expand...

Stirplates aren't for moving the yeast. They are for moving the water, and thus maximizing the oxygen pulled into the beer at the surface.

The yeast will consume simple sugars until the supply is exhausted. By decanting, and adding more wort, you can grow more yeast.

So what your saying is it's easier to just make 2 starters and decant and pitch both. 2x 1L starters = 1x 2L starters

Read this page.

The Northern Brewer Homebrew Forum • View topic - Stir Plate FAQ

It answers all your questions, and tells you how to do what I failed to explain properly earlier.