I've seen plenty of data and apps that help you estimate the viability of a liquid yeast culture. But I haven't seen a lot of data about dry yeast. I like using dry yeast for 1 gallon test batches and experiments, and it would be great to understand how much healthy yeast I'm actually pitching.
For the sake of argument, lets assume I'm asking about yeast that has been properly handled and stored at 40 degrees F. Lets also assume i properly rehydrate with water before using.
Mr Malty Pitching Calculator seems to estimate that liquid cultures are < 1% vaible at one year. But it looks like dry yeast is still 68% viable when a year old.
What are some good references on this subject, and how can I refine my control of dry yeast pitching rate?