Yeast starter step-up?

I keep reading references to stepping up a yeast starter, but I can't find any posts that explicitly spell out the process.

Let's assume I'm planning a brew, and Mr Malty tells me I need a 2L starter. Let's also assume I currently have a 1L container available to me.

Would the following be possible:
- Prepare a 1L starter
- Let the yeast do their thing for 18-24 hours on the 1L starter
- Chill the starter for 24 hours, decant
- Prepare another 1L (well, a little less I guess) of starter wort
- Add the new wort to the yeast slurry and let it rip again
(- Possibly repeat)

Would that work, or would the space contraints in the 1L vessel cause stress on the yeast? Is this basically what people mean by "stepping up" a starter, or is that more like doing a 2L starter in a 2L flask, then pitching the slurry to a larger starter (4L, 5L, etc) afterward?

Primarily, I'm trying to decide if I can do a starter with equipment I already have on hand, of if I should be investing in a 2L vessel of some sort (yes, likely an erlenmeyer flask).

Do you have a growler? Those work well, and I've used the 1.75 L liquor bottles with success in the past as well.

Yes, you have it right. You will actually get a bit more yeast by stepping up than by just making all 2L at once, which IMO is a good thing.

If you aren't using a stir plate a PET soda bottle is the best 2L starter vessel. Every time you have a chance you can agitate it (to evolve co2), squeeze the bottle so no headspace remains (remove co2 from headspace), release the bottle (draw air into headspace), and agitate again (dissolve air).

This accomplishes the same things a stir plate does (agitation and gas exchange) intermittently which is better than not at all.

Geez, I was thinking of several different things (Ball jars primarily) and never even considered using a growler! Definitely have one of those available for starter-duty!

So, if I plan to shoot for a Saturday brew-day, working backwards:
- I'd want to put my finished starter in the fridge Friday morning through Saturday mid-afternoon so I can decant and pitch slurry
- Wednesday night I'd decant my original 1L starter and step up the 2nd 1L of starter wort, give it another 36 hours or so to do its thing
- Tuesday night through Wednesday night I'd place my original 1L starter in the fridge
- Sunday morning I'd prepare my original 1L starter, give it about 36 hours to do its thing

In my case, I don't yet have a stirplate (still deciding whether to go the DIY route or purchase one - either way, that'll be for a future batch) so I do plan to agitate this starter as frequently as I'm able.

If I went 1.5L for each step instead of 1L, if Mr Malty suggests just over 2L of a starter, would I run into any problem from over-pitching?

Mr malty advises against using the same amount of wort when you step up a starter. Supposedly you overpitch if you don't increase the 2nd step. He states 5-10 times is best but doesn't really specify what the acceptable minimum step up is

If you decant a 1L starter and add more wort that doesn't make a 2L starter. It makes a big 1L starter. Think of it like this. If you have a 1L starter of wort you have 10 units of food (pretend with me), and you add 3 yeasts (again just an easy example), the yeast grow and ferment your first 1L starter. Now you have 6 yeasts in your 1L flask. Now you decant and add 1L of wort back to you flask. Let it grow and ferment, you would end up with 9 yeast not 12. The reason for this is because now that you have more cells each one gets a little less food. In the first starter each cell got 3.3 units of food to grow, now in your second starter each cell gets 1.6 units of food.
You sound like you have the general idea. What I do when growing from agar is 10ml to 40ml to to 460ml to 3500ml. I don't decant when growing yeast.

terrapinj said:

Mr malty advises against using the same amount of wort when you step up a starter. Supposedly you overpitch if you don't increase the 2nd step. He states 5-10 times is best but doesn't really specify what the acceptable minimum step up is

Click to expand...

That's interesting because in his book "Yeast" he gives an example where a 2 L starter was made then decanted and another 2 L was added on top of that. Perhaps he was just trying to illustrate a point and if so then it was a poor example.