John recently had a dilemma. He needed to rep itch some yeast into his braggot after a long a tiresome ferment. Worried that some fresh yeast was needed at bottling he looked to the fridge. All he had away an older package of white wine yeast. He rehydrated the yeast in some water and pitched it in hoping for the best. This week he asks the question: “How old is to old for yeast?”

The first thing going for John in these situation is that he had a dry yeast packet that had been stored in the fridge. Dry yeast tends to have a much longer shelf life than liquid yeast due to its nearly nonexistent metabolism while dry. You should always consult the side of the package for an expiry date or a packaged on date. In general these things will give you an idea of how old the yeast it.

Normally, under ideal conditions these things can be revived. Dehydrating the yeast and then putting old yeast into a mild starter (1.025OG) is a good idea. The little bit of sugar will encourage the yeast to start some activity. Within 30-60minutes properly rehydrated yeast should start to show some singes of CO2 production. This means there are some live cells in there. It doesn’t mean they are all alive or that you have a pitchable quantity but it does mean you have a shot at redemption.

The next step would be to let the yeast continue to make up in this sugar solution. Once it goes to completion, you can pitch it in a new volume (not more that double in size) with more sugar (this time not more than 1.040OG). When that once completes its process I’d recommend cold crashing it and seeing how much yeast volume there is. From there you might be ready to decant the spent liquid and go to a true 1-2L starter wort. Proceed as usual.

Ultimately there is no real good answer. Is the yeast too old? You have to put it in some sugar and see if its alive or not. No date on the package is going to tell you that. Like many things in home brewing you need to try them out and experience it yourself. Experience and gained knowledge will go a lot further than any “expert” source can give you.

BREW ON!