I want to reuse the washed yeast from a previous batch of beer in my next batch. Should I make a starter for it? If so, how much of it? I looked at MrMalty, and it seems to me they tell me not to make a starter for this. So how much yeast starter should I make? Should I just repitch the washed yeast?
You don't necessarily need to make a starter if you are re-pitching within a few weeks because the viability of the yeast will still be pretty high. But, if you store the yeast for much time you should always make a starter. This ensures that the yeast is still viable and it will help ensure the yeast are active so you don't have a long lag time during fermentation.
I frequently wash yeast for use in future batches and always make a starter. It gives me a little peace of mind because I know for certain that the yeast are viable before pitching.
Disclaimer: This answer has not yet been tested by experience.
I saved the yeast from our last 4 brews, but I haven't used any of it yet. Although it was my impression that the washed yeast could simply be repitched, I was planning on treating it like dry yeast, and proofing it just to test my storage more than anything else.
You'll note the quantity of yeast slurry does change on the calculator, and I don't know about you, but when I adjust the sliders to represent the near solid yeast cake I've saved, it looks like I only need half of what's there, so a starter while perfectly acceptable, should be unnecessary.