I was wondering if anyone had a go-to procedure for growing a big (lager-like) pitch? I’m not going to be brewing soon, so cannot make an extra gallon to use as a starter. Does anyone ever just make a gallon or two of simple wort with DME and use that as a BIG starter?
My largest flask is 4L, so when I’m making a starter for a lager I will do a 2L starter, let it ferment out, decant the liquid, then make enough fresh wort to fill the flask to the 4L mark and let that ferment out. I’m using a stir plate.
Chill the 4L starter, decant the liquid and pitch the remaining yeast.
I usually start this process about a week before I brew.
You certainly could take a 1 gallon container, make some wort, add some O2 and pitch the yeast. You don’t need a stir plate but you’ll get more yeast growth with one.
using DME to makes starter wort is pretty standard. aim for 1.030ish the two step is a good way to get a really big pitch ready
For the Dunkel that is fermenting, first went into 1 L, then 3, then that got split between 5 and 2 litreeflasks, all on stir plates. So I had the slurry from about 6 litres to pitch. Lots of yeast is what one needs for lagers. Make it with DME, shoot for 1.030 to 1.040 in the starter. I use 100 grams of DME/liter, or a little less.
According to the trials from White and Zainasheff’s Yeast the yield factor starts falling around 1 vial / 2L (50m/ml), but is still fairly high at 1 vial per 8L. In a 1.036 simple starter, yeast will double 1.1x for 1 vial in 2L, 1.8x for 1 vial per 4L, and 3x in 8L. You can see how doubling increases at a lower rate than volume.
Yeast growth is sensitive to pitching rate. High pitching rates will result in propagation-type growth, low pitching rates will result in beer-like growth. The growth-vs-starter-size curve gets flatter and flatter the larger your starter gets, and approaches a limit of 600b cells, regardless of wort volume. We can use this info to our advantage when planning yeast starters.
For instance:
A) 1 vial = 100b cells > into > 8L = 400b cells (3.0 doublings, plus 100b cells we started with).
For a 2 step starter:
B) 100b cells > 2L = 210b (1.1 doublings) > 2L (0.5 doublings) = 315b total
C) 100b cells > 2L = 210b (1.1 doublings) > 4L (1.1 doublings) = 441b total
For 3 steps:
D) 100b cells > 2L = 210b (1.1 doublings) > 2L (0.5 doublings) = 315b > 2L (~0.25 doublings) = 394b total
Even though C and D had the same total amount of wort (6L) the growth in D was lower because of the increasing pitching rate at each step limiting the growth. Even though C used 2L less wort, it grew 41b more cells. C had 25% less wort, but grew about 10% more yeast. D used 25% less wort than A but grew almost as much yeast.
Now, for simplicity’s sake it may be more practical to just make one 8L starter, but if your glassware isn’t large enough, or if you’re using DME to make your wort ($$$) then perhaps doing multiple steps makes more sense.
EDIT: As Tom pointed out, the term “doubling” that White and Zainasheff use is actually a multiplication factor, not a true “doubling” figure.
This is two doublings. If it doubles three times, 100B cells becomes 800B cells. I don’t have my copy of yeast in front of me, is it reported as doublings or cells counts?
I see what you mean. The table labels the column “Number of Doublings” but I think that’s incorrect. It gives total cells and new cells as separate columns. Working backwards from the table it seems it gives the total cells like: x + x(# of doublings), and in the true sense of the term “doubling” the formula for doubling twice should be like (x)*[2^(# of doublings)].
It sounds like they list how much it multiplies, not doubles. Which is fine, but it’s not the same thing.