Why must starters be so large? Not understanding the concept of liter + starters

So why is it that the size of the starter is so important? If I were to take a slant of yeast and make a half liter starter with it that contains a half cup of DME in it, wouldn't I get the exact same result as a starter with 1 liter that also has a half cup of DME in it?

I don't get the impression that the yeast won't have enough room if the starter is less than a liter, or am I mistaken? When we speak of a 1 liter vs 2 liter starter are we simply assuming the gravity is the same for both, hence the need for a larger starter?

Wouldn't a larger starter also take longer to develop those cells then? How do you know when a 1 liter starter is ready vs a 2 liter starter if you pitched the same amt of cells to begin with?

Help me out here! Thanks all!

So why is it that the size of the starter is so important? If I were to take a slant of yeast and make a half liter starter with it that contains a half cup of DME in it, wouldn't I get the exact same result as a starter with 1 liter that also has a half cup of DME in it?

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No. It's not about the amount of fermentables. The yeast are going to reproduce until they reach a maximum concentration. Something on the order of 75-100 million cells per ml if I remember correctly. The way you get more yeast cells available to pitch is by creating larger volumes of the culture.

The size is also important because you want yeast to be as healthy as possible. This is why we stick with 1.030-1.040 SG starters and vary the volume. The point of a starter is to propagate the healthiest pitch possible.

Sounds like i've got a starter that needs sizing up in that case.

So my last question is, with the different size starters it should logically take longer for the yeast to be ready in a larger starter. How does one know when they're good to go?

Thanks again!

Gravity sample, or just wait for the krausen to fall. Since attenuation isn't that important, I wait until the krausen falls and throw it in the fridge to cold crash.

Well if you want to get super technical, you can purchase a hemocytometer and a microscope (and some methylene blue) and count yeast cells. What I do is just plan it out so that my starter is going about 18-36 hours before I need to pitch it.

there are charts that will show you the amount of yeast cells you will get based upon starter size and amount pitched into the starter. You can get away with a smaller starter for instance if you don't have a large flask by using 2 vials instead of 1 to pitch into the starter. For high gravity beers that need 400 billion yeast cells or something like that it is a good option. If you haven't read "Yeast" I would pick it up, it has a section dedicated just to starters. Stir plates also increase the amount of yeast cells in a smaller starter as opposed to just shaking occasionally.

As for time frame I haven't noticed much difference based on size. Maybe if you were going really big but on a stir plate it gets going pretty quickly. I usually make mine 2 days ahead on big starters and then turn it off the night before and decant most of the liquid off before pitching. Smaller starters I will just make the day before and pitch while they are still actively fermenting.

seabass07 said:

Gravity sample, or just wait for the krausen to fall. Since attenuation isn't that important, I wait until the krausen falls and throw it in the fridge to cold crash.

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Do you re-warm this yeast on brew day?

Rick

Yes. Decant off most of the liquid and let it get up to room temp. You want your yeast to be close to pitching temp when you dump them in.

I think the goal is also to give the yeast an ideal environment to reproduce in. 100g of dme in .5L is going to be rougher on the yeast than 100g of dme in 1L due to the concentration of sugars and resulting alcohol production. Consider, rather, how much yeast you will get from X liters of 1.040 starter solution.