Brewing With Oats : Oatmeal Stout Case Study

If you want to add more texture and body to your beer, brewing with oats is a good option. Here I look at some of the issues, focusing on an example oatmeal stout brew day.

brewing with oats

The use of adjuncts (grains other than barley) in traditional brewing was usually a result of economic considerations. Corn, oats and sugar are cheaper than malted barley.

Despite this, many beers make use of adjuncts to such great effect that’s it’s hard imagine them without them. One great example is the use of oats in stout. They contribute a thick body that works with the dark roast flavours to produce a classic, flavoursome beer.

You can malt oats and brew with those, but that’s unusual. It’s more common to add a small amount to an otherwise barley based beer, as I’m going to demonstrate below.

Why Use Oats At All?

Oats contain starches and gums which thicken the body of a beer. These remain in the beer after fermentation and are felt as an oily texture in the mouth.

If you’ve ever made porridge you’ll have the seen the effect of oats on water. They change it from something bland and, well, watery, to a thick and creamy gloop.

The quantities used in brewing are not usually that extreme, but the results are similar.

Oats in Brewing

Medieval brewers used oats often, but that practice was over when they started using oats to make stout at the end of the nineteenth century. The amounts at that time were usually quite small.

During the second world war, brewers in Britain began to use more oats in their beers. Barley was scarce and was needed for bread and other staples, and brewers were told to investigate bulking up the grain bill with other products.

Initially there were minor issues to deal with, amongst them the problem of haze.

You shouldn’t have to worry about this in your home brew because you’re generally working with small percentages. In any case, dark beers are less sensitive to visual issues, and home brew doesn’t need to be beautiful as long as it tastes good.

There were also concerns about an increased risk of bacterial infection.

This article explains a series of test boils on worts with and without oats. Although the batch with soon went bad, the experiments also confirmed the preservative qualities of hops. When added to the boil, they eliminated all signs of mould for the period of the experiment.

The above information came via Shut Up About Barclay Perkins, which I suggest exploring more if you’re interested in using oats in brewing.

Oats In Your Home Brew

Brewers developed the mashing process to extract starches from grain. Enzymes in the grains, usually produced during malting, convert starches into sugars. This is a natural process that ordinarily provides food for the growing plant. Brewers hijack this process to make the sugary, malty liquid called wort.

While mashing malted barley is fairly easy, the starches in oats are harder to get at and need to be gelatinised first.

Fortunately for home brewers, rolled oats and instant oats have already had this done to them. In manufacture they’re heated and broken down into something that can be added directly to the mash tun.

Mashing Tips

Oats don’t include any enzymes so mash them with a malted grain (e.g. pale ale malt) for the starch conversion to work.

Smaller cut oats work better as they have a larger surface area for the water to work with. This same logic explains why you grind malt before mashing.

My Experience

To test these theories, I developed an oatmeal stout recipe using the BJCP guide. This revealed that the average oatmeal stout recipe has 5 – 10% of the grain bill as oats. Those numbers represent a sliding scale description of the beer’s body, from silky to oily.

With only 5% oats, I performed a normal mash, but if your recipe is for a thick and oaty stout there are instructions here for how to deal with the mash in that case. Essentially it involves adding a low temperature (40 to 50°C) rest to the mash schedule.


Here is the recipe I developed:

Recipe Volume
14 litres

Pale Ale: 2.4 kg
Munich: 0.8kg
Crystal 120L: 0.4kg
Black Patent: 0.2kg
Oats: 0.2kg

Mash Time
90 mins

Mash Target Temperature

Fuggles (4.8%): 20g for 60 mins
Kent Goldings (5.3%): 25g for 20 mins
(35 IBUs)

Danstar Windsor Dry Yeast

Assumes 60% efficiency


As usual, I used BIAB to make the beer and mashed as usual on the stove top. I was aiming for 67°C so the beer would retain some body and sweetness, but I struggled to maintain that temperature throughout.

The mash hovered around 65°C so I’m expecting a slightly drier, more attenuated beer.

For this particular brew, I decided to follow the advice of Gordon Strong and leave the darker grains until later in the mash. In this interview he makes a very convincing analogy between coffee and beer:

You wouldn’t leave coffee brewing on the stove for an hour and a half before drinking because it would be bitter and unpleasant, so why do it with malt.

In my ninety minute mash, I had the pale, Munich and oats from the start, only adding the darker grains for the last thirty minutes. The colour came through, so I’m optimistic about the taste.

If you use large quantities of oats be careful as they can turn into a messy glue that will cause dough balls and possibly block the mash and make draining difficult. You will probably need longer to drain whatever happens – I did.

brewing with oats gummy residue in mash

The mash itself was uneventful, aside from the long drain time. When I lifted the bag half the wort came out with it.

brewing with oats mash

The coffee analogy makes even more sense when you see the boiling wort with its thick espresso head.

brewing with oats oatmeal stout froth

I spent much longer than usual turning over the spent grains to get the wort out of the bag. I can only imagine that the oat gums had caused a blockage in the fabric.

brewing with oats oatmeal stout spent grain

I achieved a final gravity of 1.050, almost exactly on target. Fermentation was vigourously underway within twelve hours, in part because of my freshly harvested yeast.

Update: This beer came out a bit pale for a stout. I’ve published an updated recipe here:
Oatmeal Stout: The Proper Recipe

Do you use oats in your beer and how do you find working with them?

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  1. Couple questions….

    1. Oats vs. maltodextrin – I’ve only used maltodextrin once, so I don’t know … would oats provide greater body?

    2. Have you used oats with extract brewing before? It’s something I’d like to try, but not sure what would be best practice: steeping with grains at start of boil or throwing some in the boil wholesale and trying like hell to siphon around them when moving to primary.

    • John

      Hi Bryan,

      My understanding is that the oats need to be mashed with base malt for the starches to be converted. Otherwise, you end up with raw starch adding body to the beer instead of dextrins, and starch is more susceptible to infections.

      That would suggest that maltodextrin is more appropriate in a situation where you don’t mash, i.e. in extract brewing.

      The benefit of oats, I guess, is the additional flavour that comes through but I think you have to toast them for that to become really noticeable. I didn’t particularly taste any oat flavour in this beer, for example, but the body was thick.

      As for your second question, I haven’t tried with extract brewing but I’ve heard people say (contradicting the mash advice I’ve just given!) you can steep oats and get the desired body, but to a lesser extent than with a full mash.

      I think that would be your best option because the Mad Fermentationist recently tried boiling oats and the outcome wasn’t as impressive as he’d hoped.

      Hope that helps and thanks for getting involved!

  2. chris

    Do the oats added in the making of Samuel Smith oatmeal stout make it any less healthful than a regular stout?


    • John


      The honest answer is I don’t know, but I don’t see why they would.

      I suppose neither are particularly healthful!


  3. Tom List

    Hi Bryan,
    A couple of Christmas seasons ago I played with the idea of a “Whoat” beer, wheat and oats. I started with a basic Dunkel recipe but I toasted the oats and steeped them in a grain bag separate from the wheat. I added one can of tart cherry extract and called it “Cherry Oh Baby”. It was pretty awesome.

    What do you think would happen if I tried the same idea, but started with a tripel recipe instead?