I'm planning an Oatmeal Stout as my next brew. I've used oatmeal in previous batches, but have never really been happy with the results. They've lacked the mouthfeel I've been going after.
I've been using just regular rolled oats from the local bulk food store. Advice I've found online isn't clear whether you need to boil oats, or can just throw them into the mash, so I decided to do a little experiment last night!
I prepared two batches of oats. Into each batch went 750mL water, and 90g oatmeal.
For batch 1, I heated the water to 70C, tossed in the oats, stirred it a bit, and then let it sit for 20 minutes.
For batch 2, I brought the water to a boil, tossed in the oats, returned to a simmer, and then let it simmer for 10 minutes.
I strained a few spoonfuls of each through a mesh strainer.
It was immediately obvious that batch 2 was thicker. It had actually absorbed most of the water. The strained liquid was more opaque, and had a thicker consistency. According to my refractometer, it had a SG of 1.006.
By contrast, batch 1 was still pretty watery. The strained liquid was fairly thin, although still opaque. There was no noticeable increase in SG vs. tap water.
tl;dr Boiling my oats resulted in a much thicker sample, will be trying this in my next oatmeal stout!