What's the best way to prepare grain for mushroom cultivation?

The 3 most important aspects of grain preparation are to achieve an uniform, correct water content, to kill all contaminants and to get a shakeable substrate.

There are 2 main approaches to grain preparation:

Method 1.) Rinse the grain several times under flowing water and simmer it until the grains are soaked and begin to explode. With rye the simmer time is around 45 minutes, with millet or millet based birdseed around 30 minutes(but it strongly depends on the individual brand)
Then strain the cooked grain for 20 minutes, fill in jars, screw on a lid fitted with a filter and pressure cook for 1 hour.

Method 2.) Fill the jars directly with the proper amounts of grain and water and pressure cook for 1 hour. If one experiences bacterial contamination problems the grain can be left to soak up to 24 hours before pressure cooking to allow bacterial endospores to germinate.

Basic rye recipe for 1 pint jar:

- 100g(3.5 oz ~ 125 ml) rye
- 105g(3.9 oz =105 ml) water
- knife tip full of gypsum

Basic millet or birdseed recipe for 1 pint jar:

- 100g(3.5 oz ~ 140 ml) birdseed
- 70g(2.8 oz = 70 ml) water
- knife tip full of gypsum

If you are going to prepare rye for producing spawn, you might use a tad less water( I use 100g in that case)

Fill into the jar, screw the lid fitted with a polyfill filter or a tyvek filter on the jar and pressure cook for 1 hour.
After the pressure has settled, using protective oven mitts or a towel, take the still hot jars from the cooker and shake them well to mix the more wet and drier kernels.

The water retaining capacity can vary depending on the grain quality, the type and size of the pressure cooker and on sterilization time.
The goal is to achieve the highest possible water content without alowing to many grain kernels to explode and without producing a soggy substrate.
It's best to make a batch of test jars when one acquires a new grain for instance 100g rye and 100, 105, 110, 115 and 120g water.
Then you'll see which water content provides the best result for you.

Which one of the 2 methods is better? It's mainly a mattter of personal preference, try both and see what works for you.

Links to teks:
Tabletop Mushroom Cultivation
Grain for Simple Minds