Whenever I make a starter, I always decant off the ‘beer’ and just pitch the slurry. I recently upgraded to a 2L flask, am brewing a 1.078 ale, and according to Mr. Malty I should prepare a 1.7L starter using just one White Labs Vial. My question is: if I’m decanting off the ‘beer’, what difference does the volume of the starter make, as long as it’s around 1.040 OG? Does volume correlate to yeast growth?
Yes it does, but it’s not linear. Isn’t that why you “upgraded” to a 2l flask.
http://www.yeastcalc.com/index.html
This lets you play with sizes and see the growth differences.
and for what its worth - many experienced folks on this site have said 1.40 is not optimal for a yeast starter. healthier cells are created south of 1.035, and 1.030-1.032 seemed to be the recommendation.
The difference is at a given concentration of wort a larger volume of starter has more sugar for the yeast to eat. Volume doesn’t correlate to yeast growth, but total amount of sugar does.
Got it. Thanks for the clarification.
My understanding is that higher sugar content actually starts the yeast on an anaerobic cycle (like you want in beer) while the lower sugars can still encourage aerobic yeast growth resulting in better cell wall strength and more healthy yeast. The starter is supposed to grow yeast not make beer - yet. I’ve had great luck with starters down to 1.025.
Maybe tschmidlin can chime in?
If you’re thinking of the Crabtree Effect, there is a gravity below which the yeast won’t ferment, but it’s about 0.5°P (1.002), so it isn’t really a practical way to grow yeast unless you have a method for continuously feeding the culture, like the yeast labs do. But as long as there’s some oxygen available, the yeast will continue to reproduce as well as ferment the sugars anaerobically. Which is why increasing access to oxygen results in more growth.
What he said. 
Yeastcalc mentions an “ideal gravity” of 1.037 for a starter - perhaps that was done to keep the grams of DME to milliliters of water ratio at a nice comfortable 10:100.
I’ll assume the growth rate calculators were set up based on that OG, but does it really make that much of a difference in the growth rate or overall yeast health between a liter at 1.037 and a liter at 1.030?
So you can see the growth rate difference using Kai’s calc on brewers friend. I think the important difference is yeast cell health- lower gravity = healthier s cells as I understand it.
I will leave the discussion of yeast health to the microbiologists, but overall growth rate would be less at a lower gravity just because there’s less food for the yeast to eat.
since we are on the topic, anyone have general guidelines/thoughts on how big a single step starter should be? ive wondered if a one step 2.5ltr starter at 1.035 is fine, vs. 2 steps at 1.25lt each.
one step at 2.5 liters is probably even preferable. your growth rate will be higher and therefore, if I am understanding this whole yeast thing, the average age of the cells will be lower.