The way I see it you can use the beer grains in two different ways- you could ferment them in your bokashi barrel, like anything else, or you could dry them and use them as your medium for the microorganisms that you sprinkle in every time you put a deposit in your
bucket.
It depends on what else you have going into your bucket and how often you have spent grains. I brew every so often, and only every so often I have some. That goes in my bucket, along with all my other compostables.
If I had a more regular supply, I'd dry it and mix it with my microorganism serum- I know some people use bran, which is pricey for me so I`m always playing around with different options. Currently I mix a small amount of bran that has the spores with either
wood shavings or the wood pellets that make up the litterbox for my kid`s pet rats, hot composted with
coffee grounds for a few months before they get put in with the bokashi starter. I think spent grains would make a great medium.