300l roasted barley to 500l

Does anyone know how to roast 300l barley to 500l (temp and time)? I can only get the 300l locally and I would like to make an Irish dry stout this weekend.

From everything I have read doing the very dark malts is nearly impossible at home since they are so close to being charred.

If you really just had to give it a shot I would use an air-pop popcorn machine. I use one for roasting coffee and it does a pretty good job of it. The circulating air ensures an even toast and it allows you to keep an eye on things as you go. Once they hit the color you want quickly dump them into a metal strainer and toss to cool.

That said, I would just go ahead with the 300L, and use a bit more, it won’t be exactly the same, but it should still be tasty.

Edit: Another option is to use black patent, I find it very similar to 500L roast barley. Maybe a combo of it with the 300L barley. Something to think about anyway.

The kilning temperature is 200C (400F). Time is rather tricky, since you'll be starting with 300L. I'd start with 30 minutes and check the smell. If there isn't a faint charcoal smell, give it another 15. Repeat as necessary.