Can you tell me how many agar plates this 4 oz packet will make?

Hello-This is a difficult question to answer. It really depends upon the size of the petri dishes you are charging and the amount of nutrients you add to the mixture. 15 grams of our 900g/cm2 gel strength straight agar agar will gel 1 liter of distilled water. 1 liter of solution will charge approximately 40, 100mm x 15mm polystyrene dishes at an average fill of 25ml per dish. I hope this information is helpful. Please let us know if we can be of additional assistance.

I use 1/2 teaspoon per cup. Sprinkle on top of some cold water and bring to a boil. Simmer for 5 minutes and let cool. Add other ingredients like juice. Example use 2 teaspoons of agar with 1 cup of water and after simmering add 3 cups of apple juice.

Does this have an expiration date?

Yes it does have an expiration date. We don't have the original package it came in so I can't tell you how long the expiration date is. Per your question I looked into it and it look like agar has a 2 year expiration date from the time it was manufacturered. If store properly, like in the refigorator, it should last longer than 2 year. we refigerate alot of things to slow down the aging of it.