Brewing a better Oatmeal Stout is an ever evolving goal of mine. Oatmeal Stout was the second style I brewed when I first started brewing many many batches ago. To me Oatmeal Stout should be roasty with a decidedly chocolate like lean. It should be smooth, silky and balanced. There should be a well perceived presence of toast bread or biscuit like quality. There should be a mild caramel that pulls it all together. Three things come to mind to put you on the path to developing YOUR best Oatmeal Stout.
First of, like so many beers, you have to nail your fermentation. For the most part this is an English style stout. You want some supporting fermentation derived ester qualities in the beer. This is perfectly delivered by most English Ale yeast strains. Problem is, English style yeasts tend to have medium to ‘less that desireable’ attentuation potential. These yeasts often ferment fast and fall out a little early. In order to get the crystal malt, the chocolate malts and the oatmeal to all play well at the front of the stage you have to get all the other residual fermentables fermented out. For me I accomplish this by starting my fermentations a little cool (62F) for the first 48 hours. Then I set the temp to 66F and let fermentation start to take off for two more days. Then I ramp it to 69F and let it ride for three more days. After that I set the temp to 72F and let it go for another 7 to 10 days. By doing it this way you can coax most English Ale strains to go the distance and reach their reported higher end of attenuation. Of course, a moderate amount of O2 and some yeast nutrient helps too.
I wish I could tell you what my favorite yeast strain is…but I don’t think I am quite there yet. For the last two years I’ve been have good luck with WLP013, London Ale yeast, but I have used WLP007 when I find myself struggling with temp control. WLP002 can be perfect if you know you can dial in the fermentability from your mash regime, use great temp control and have a very active kick-ass starter.
Second step is to blend your crystal malts. My main point here is to develop some interesting caramel background tones and complexity by using two different crystal malts. Lately I really like a 75/25 split of C40 and C80. But its often a toss up of C80 v C120; depends on my mood. You need to explore these combos based on your own palette. You can start mixing three together but its a tight wire to walk on for sure. In order to get appreciable flavor from any malt there is a minimum you need to use (again palette dependent). So when you go to three you might find yourself drifting into two much crystal malt which makes the beer harder to get dry enough. Stick with two in combo seems to have been the best for me.
Lastly, you have to toast your oats. Not all of them maybe a half to a third. I have found that I need at least one pound for a typical 5 gallon batch to be just plain oats for the requisite mouthfeel goal. Toasting an additional 50% seems to have been the magic number to get that biscuit like quality without actually adding yet another malt (i.e. biscuit malt) to the grist. Adding another malt to the grist then brings us back to point #1 about dryness and fermentation.
Oatmeal Stout has been a fickle beast for me. Sometimes that first pour of a new batch is just perfect, then others seem off the mark. But these three points have driven it home for me and seem the common thread when I do get batches that seem close to divinity.