How long does it take for a yeast starter to do it's thing?

[Muz]

I've always wondered this. I usually use BeerSmith to work out the size of yeast starter I need. Then recently I was trying to revive a particularly old yeast batch and a friend put me on to yeastcalculator.com. both seem to do they job but I've always wondered what is the a) minimum and b) optimum time to leave a yeast starter before pitching? I mean if one of these calculators recommends a starter of X litres and Y grams of DME to get to Z billion cells, how long will this process take to get there?

I read something recently (sorry, can't find it now) that said 48 hours means you're pitching when the yeast are at the peak of their activity. Then I read someone's process where they left a yeast starter for only four hours. I would have thought that wasn't enough time. Anyone got some science to answer this one? Can you leave a yeast starter too long?

 

[soreba]

If it's old yeast, it will take longer. Depends on how many cells you start with.
My starters are done usually around the 24 hour mark - krausen gone and activity settled, then i crash and pitch. If its a 6 month old liquid yeast vial then usually 48 hours.

 

[Muz]

OK, so where do you get those times from? I guess a krausen would give you an indication of where the activity is at. I use a stir plate so I don't get this visual feedback. though I do find the starter gets whiter as the starter progresses.

 

[soreba]

OK, so where do you get those times from?

My experience from trial and error

You should be getting some kind of krausen on a stir plate.. I have a 4 litre starter on at the moment.. will take a pic when i get home.
If its old yeast sometimes it wont show any feedback, in those cases i usually step up again to make sure of viability.

Edit: See here https://www.instagram.com/p/BzLWFPyHqMj/?igshid=14hh13n1190ku for what it should look like... although this guy spins his really fast, mines a bit slower.

 

[Muz]

Thanks. Yeah, I guess I get something similar. I never really thought of it as krausen. I just thought it was bubbles caused by the spinning and the overly aerated wort it produces. I'll pay more attention next time.

I was also just thinking I could take a gravity reading and see where things are at right? Or get a really small tilt...

 

[hoppy2B]

The 4 hr starter might be what they refer to as a vitality starter. I think it is just meant to oxygenate the yeast and getting it started for pitching.

 

[Kev R]

I checked the gravity on one at 24hours because i thought the yeast was no good. Turned out it was done.
I do 2lt starters at 1.035. Not had one go past 48 hours(ale). Turn of the stir plate if it starts to settle I consider it done.

 

[sponge]

Also depends if you're pitching an active starter (high krausen) or finishing ferment and decanting.