Rye grain is stupid easy. Popcorn grains proved to be difficult for me to hydrate.

My recipe for hydrating Rye grain: let whatever amount you have soak inside a bucket for 12-24 hours. Just tap water. Make sure the water is above the grains. They'll expand enough that they will for sure break the water line. So put more water in that you think you might need.

Then - pour the water out. I like to wash off as much "dust" as I can aka Pour fresh water in and then pour it back out without spilling any grain.

Then separate the grain into pots and put them on the stove with water - until they boil. Once they boil let it sit there for just a minute and then remove it from the heat.

From there - you'll be ready to let them drip off excess water in the sink - and then scoop them into jars for pressure cooking.

basically all grains are the same - hydrate in tap water for 12-24 hours - then boil them on the stove for literally just a minute - then let them drain.

By then your rye grain will still be holding it's shape for the most part but also be packed with water.