When to crash chill a yeast starter

[Yorg]

I have read somewhere that after a cerain number of hours, the yeast count of a starter does not increase, but that the yeast are simply tiring and ageing as they complete the starter fermentation. The suggestion was that - I think - at high krausen the starter could be crash chilled to keep the yeast young before pitching.
Can anyone confirm / deny this as a desirable brewing practice?

[meisterofpuppets]

There are two schools of thought on this one. One is to pitch the entire starter at high krausen the other is to let the starter ferment, then crash it. For small starters, I prefer the former, but for large ones, I use the latter.

[Digger]

When using a stir plate, how can you tell when you have reached the maximum yeast growth?

[Yorg]

Why do I want to know?
Because I want to brew tomorrow, but it will not be fully fermented out.
Rather than delay my brewing, I am crashing it tonight, after about 3 days, so that I can decant the starter liquid of 4.5 liters /5 quarts.
I don't want the DME starter in my AG.
So I was wondering if crashing it before fully fermenting it out was going to be detrimental.

[seanhagerty]

Wow thats a large starter.

The way to tell if its doine is to take a gravity reading. If the yeast has eaten all the eatable stuff the gravity will be low. If you look, you will notice the starter wort turn cloudy and then a clearing will take place. When that clearing takes place, I usually consider mine done and crash it or pitch it.

Sean

[boobookittyfuk]

When using a stir plate, how can you tell when you have reached the maximum yeast growth?

there are only two ways to know that yeast has reached cell growth

1) microscope and hemacytometer counts of yeast cells

...or the much easier method...

2) Read the absorbance at 600nm with a spectrophotometer

chances are you can't do either of these...so all you can do is guess.

[boobookittyfuk]

I don't want the DME starter in my AG.

then do a mash for your starter.

don't cold crash a starter...its counter-productive

if you cold crash then you WILL have a a much longer lag in fermentation then if you just pitched the entire starter. Not only that but by decanting off the top, you are tossing away the best yeast in the starter. If you were going to make a large starter, cold crash it, decant the top, you might as well just pitch 2 packages of yeast. Chances are you'd get a better fermentation for your dollar by just pitching more packages of yeast than to do the silly cold crashing that people do for some reason.

[Grist Licker]

I don't want the DME starter in my AG.

then do a mash for your starter.

don't cold crash a starter...its counter-productive

if you cold crash then you WILL have a a much longer lag in fermentation then if you just pitched the entire starter. Not only that but by decanting off the top, you are tossing away the best yeast in the starter. If you were going to make a large starter, cold crash it, decant the top, you might as well just pitch 2 packages of yeast. Chances are you'd get a better fermentation for your dollar by just pitching more packages of yeast than to do the silly cold crashing that people do for some reason.

Yes yes yes! BBKF is right on this one. To put it another way, when the yeast sense their food supply dwindling and their byproducts accumulating in the wort, they start building up their glycogen reserves and prepare to go dormant until conditions in the environment improve. When you pitch these hibernating guys into fresh wort, they sense the right conditions for growth and wake up. They start taking up oxygen and building up their cell walls so they are strong enough to handle passing sugars and other stuff across the membrane, and so they can bud off daughter cells. Yeast need to pass through their normal phases to be healthy and perform correctly. Cold crashing at high krausen will stun most of your yeast and they will not recover. They are in the fermentation phase and are not prepared for the cold. Some will likely make it through, but the net effect will be an under pitched wort.

If you have a heavily oxidized starter, you will need to ferment to completion and decant. Otherwise, just recalculate your recipe to include the DME in the starter and pitch the full amount. Maybe 1/5 of your wort will be DME but I don't think you will notice any difference in taste. Many brewers, pro and amateur use DME to bring a wort up to target gravity. Also, to reiterate what BooBoo said, if you decant at high krausen without cold crashing, you will be tossing out all the healthiest yeast and actually selecting for poor performers that flocculate out early.