Oatmeal Stout

Close your eyes for a moment and think oatmeal. Chances are you’re imagining Mom, or somebody’s mom, with a piping hot bowl of stick-to-your ribs breakfast nutrition. A flashback to the Old Days when you, or whoever else you’re picturing, was a kid.

Maybe that imagery explains, at least in part, why oatmeal stout is becoming so popular among homebrewers and other beer aficionados. After all, what do you see when you close your eyes and think about brown ale? Another reason oatmeal stout is gaining popularity is that with its uniquely smooth texture and its rich, roasted, chocolate flavors, it simply tastes great.

This style was brewed through the 1950s in England, but lost popularity and eventually became extinct. Samuel Smith’s Brewery of Yorkshire brought it back into production in 1980. Subsequently more and more breweries and microbreweries have offered their own versions of oatmeal stout, including Young’s, Anderson Valley Brewing (Barney Flats), and Breckenridge to name a few.

Homebrewers have long sought to brew oatmeal stout, which is a variation of a sweet stout or “cream stout.” To be true to the style, brewers typically use English two-row pale ale malts. The chocolate taste comes from chocolate malt, the roasted taste comes from roasted barley, and the hints of caramel from crystal or caramel malts. Typically, oatmeal stouts do not specifically taste of oats. However, the oats impart th well-known smoothness because of their high content of proteins, lipids (includes fats and waxes), and gums. The gums increase the viscosity and body of the beer. The oatmeal is an unmalted grain, as is the roasted barley. So oatmeal stouts do not satisfy the German beer purity standard, the Reinheitsgebot.


The oat content of many common commercial and all-grain homebrewed oatmeal stouts is 5 to 10 percent of the grist (all the grain material, malted or unmalted) by weight. This percent represents a compromise between taste and practicality. Because the oats enhance viscosity, the more oats used in all-grain brewing, the slower and more difficult is the sparge. Sparging can take up to twice as long for the oatmeal stout compared with more traditional ale styles.

A slow sparge can be a nuisance to commercial brewers, who have production schedules to meet. However, this is not as much of a concern for homebrewers, who do not have such constraints. Nevertheless, for the all-grain homebrewer, the higher viscosity can generate problems with a stuck runoff. This occurs in sparging when liquid drains from the lauter tun faster than it can flow through the grain bed, creating a vacuum near the bottom of the vessel. The grain bed then compacts in on itself and becomes impermeable to further flow of sparge water. But you can avoid the stuck runoff by lautering slowly and patiently.

Both Samuel Smith’s and Young’s are believed to use 5 percent oatmeal in their grist, which seems to be the minimum required in a single-step infusion mash to obtain the characteristic smoothness. Many brewers prefer to use an oats content of 10 to 20 percent for an even smoother taste. These higher levels can be used if a suitable temperature rest is used in the mash temperature profile to break down some of the gum content, allowing easier sparging. There is clearly an optimum range for the oat content.

Michael Lewis, professor of brewing science at University of California, Davis, illustrates this point in in his book Stout (Brewers Publications). He describes an experimental beer made with 30 percent oatmeal that had an astringent taste, grainy flavor, and an unfilterable haze.


The bitterness level of oatmeal stouts is low to moderate. Fuggles, Cascade, Goldings, Northern Brewer, and Columbus hops are among those that have been used for the bittering. Hop flavor and aroma are usually minimal or nonexistent, but if present they should not dominate the flavor of the final beer.

According to style guidelines, an oatmeal stout has the following characteristics:

  • Original gravity (OG): 1.038 to 1.056
  • Final gravity: 1.008 to 1.020
  • Alcohol content (by weight): 3 to 4.8 percent
  • Bitterness: 20 to 40 IBU

A typical analysis of Samuel Smith’s oatmeal stout yields the following:

  • OG = 1.048 to 1.050
  • Alcohol content: 3.6%
  • Bitterness: 28 to 32 IBU.

Brewing Oatmeal Stouts

Oats have no enzymes useful to mashing. They must be mashed (or partially mashed) with a malted grain for the starches to be converted. Like unmalted barley, the starches inside are hard and not readily usable, encased within the hard cellular structures of the grain. Without further processing they cannot be broken down by the malt enzymes.

For the starches within to be converted to sugar, the oats must be gelatinized prior to use. Gelatinization is basically a cooking process in which the hard kernel coating is broken and the starch granules are ruptured and released.

There are a few different kinds of oats available to the homebrewer. With flaked oats, also called rolled oats, the gelatinization is done by the manufacturer. This is done by softening the oats with steam and then passing them through heated pressure rollers into flakes. The grain husks are removed when the oats are rolled, and in this process the flake thickness can be controlled. The heat and pressure gelatinize the starches, and these grains can be added to the mash directly. The brewer does not need to cook these prior to mashing.

Rolled oats are available in the supermarket. It is best to buy the “quick cook” or “one minute” oats. These are identical to the traditional breakfast oats (which require longer cooking time), but the “quick oats” are cut into finer pieces. The resulting increased surface area allows the starches to dissolve more readily into the water. Special flaked oats, similar to the supermarket “quick cook” oats, are available in homebrew supply stores.

Steel-cut oats are the whole oat kernels, cut up but not gelatinized or processed in any othe way. These are cheaper than rolled oats. For the starches in these to be usable, these oats must be cooked before use. This can be done by placing the oats in boiling water, two gallons of water per pound of grain. This mixture is boiled between 45 minutes and two hours, and must be stirred every five minutes. The gelatinization is complete when the liquid consistency becomes uniform. Because of the extra work and mess involved in the cooking process, you’re probably better off with pregelatinized, flaked oats.

The Gum Content of Oats

The thick consistency of an everyday bowl of cooked, breakfast oatmeal results from the high gum content of oats. These gums consist of beta-glucans, which are essentially long chains of many glucose units linked together. The difference between these beta-glucans and starches (which are also chains of glucose molecules) is in the structure of the bonds between the individual units. In well-modified malted grains, beta-glucan levels are low because these bonds are broken down during the germination phase.

In all-grain oatmeal stouts using 5 to 10 percent oats in the grist, the gumminess of the beta-glucans is usually not excessive, and a single-step infusion mash can be used. However, when using higher percents to get greater smoothness and body, you must reckon with the gums to do an effective sparge. This is done by adding a second temperature step in the mash, called a beta-glucanase rest. The enzyme beta-glucanase works best in the temperature range of 104° F to 122° F. Holding the mash temperature for half an hour in this range before the saccharification rest is sufficient to reduce beta-glucan content significantly.

A Few Tips

Options: Try varying the amount of oats, roasted malts, chocolate malts, or the Lovibond rating of the crystal malts. Higher Lovibond equals more caramel, nutty flavors. Try different hops, too.

Sparging: The sparge rate depends on the geometry of the lautering vessel, the way the grain was crushed, the temperature of the sparge water, and the temperatures of the lautering vessel and grains themselves. Thus, homebrewers using the same recipe and procedure may experience different sparge rates. If the rate is too slow and it is not possible to do a beta-glucan rest, try using some six-row barley instead of two-row barley in the mash. The increased amount of husk material provides more void space in the grain bed for faster sparging. The tradeoff is that the extra husk material from the six-row barley may increase the bitterness level of the beer somewhat. Should you desire to increase the amount of oats in the all-grain recipe, a beta-glucanase rest is probably necessary. This is done by heating the 11 qts. of water to 120° F, doughing-in the grains, and holding the temperature for 30 min. Then heat to mashing temperature, and proceed as described in the step by step.

Yeast Starter: Do not skimp and omit the yeast starter! The starter allows the wort to begin fermenting more quickly, reducing any chances for problems with bacteria. Also, the use of a starter allows the fermentation to proceed to completion with fewer reproduction cycles and fewer of the off-flavors brought about by reproduction cycles. Liquid yeast products usually give simple instructions for making starters. This involves boiling 1/3 cup of dry malt extract with 1 pint of water for 15 min. This is cooled, aerated, and placed in a sanitized bottle, after which the yeast is pitched and an air lock is affixed. Common homebrewing references give more details on preparation of starters.

Aeration: Prior to pitching the yeast, aeration is required to give the yeast the necessary initial oxygen for metabolism. This is easily done with an aquarium air pump hooked to an aeration stone. The stone and the tubing should be well sanitized before they are placed in the wort. To avoid picking up bacteria from the air, put a small piece of sterile cotton on the air inlet of the pump. This method can cause the wort to foam and overflow the container, thus you should watch the wort closely. Don’t scoop the foam off and discard it. The foam contains many important compounds responsible for beer head development, such as proteins. Allow the foam to subside, add the yeast, mix it in, and proceed with the fermentation.

Oxidation: Some brewers have found that oatmeal stout oxidizes (stales) more readily than other styles, possibly because of the extra fat content from the oats. Be especially careful not to aerate the beer during or after fermentation, particularly in transfers and bottling. After fermentation has begun, the yeast metabolize anaerobically so the oxygen is unnecessary. Also, leave no more than 1 to 1.5 inches of air space in bottles. The more air space, the greater the tendency of the beer to oxidize and spoil.

Mash-in, Mash-out: The initial mixing of grain and water, called the mash-in or dough-in, should be done carefully, in multiple steps. If the mash-in is done too rapidly or the mixing is poor, the starches in the grains can ball up and will not undergo complete conversion. Do the mash-in in three or more steps. Start by adding about 1/3 of the water in the mash tun. Mix in about 1/3 of the grain, stirring for at least 60 seconds. Next an additional 1/3 of the water should be added, followed by another addition of the grain and another minute of mixing. This is repeated once more to fill the mash vessel. Do not skimp and omit the mash-out. The mash-out at 168° F lowers the viscosity of the wort, making the sparge easier. Also, this halts all enzyme activity, ensuring that the dextrinous character of the wort will remain unchanged after mashing.

Stuck Runoff: If the dreaded stuck runoff does occur, there are two options to fix it. You can underlet the mash, using a pump to pump water back into the outlet of the lauter tun, into the bottom of the grain bed. This loosens the compacted grain bed, allowing the sparge to continue. If underletting does not work, simply mix up the grains in the lauter tun, pour the collected wort back to the lauter tun, restart the sparge, and begin again collecting the wort. Before you know it you’ll be enjoying the smooth taste of your own oatmeal stout.

Oatmeal Stout
5 gallons, extract with grains

OG = 1.054 IBU = 34

The grains are mashed prior to the addition of the dry malt extract. The oats have a negligible enzyme content. Hence the American six-row barley with its high enzyme content is used to saccharify the oats.


  • 6 lbs. amber, dry malt extract
  • 1 lb. crystal malt, 60° Lovibond
  • 1.5 lb. American six-row pale ale malt
  • 18 oz. oatmeal (quick)
  • 0.5 lb. chocolate malt
  • 0.5 lb. roasted barley
  • 1/2 tsp. Irish moss, for 15 min.
  • 2 oz. Fuggles hop pellets (4.2% alpha acid), for 45 min.
  • Wyeast 1084, Irish ale yeast

Step by Step:

Prepare a yeast starter a day or two before brew day. Crush the specialty grains and malt, and mix them with the oats in a coarse, nylon bag. Tie up the nylon bag to seal it. Heat 3 gals. of water to 155° F in a pot with a lid and add the bag of grains. Keep this pot covered, maintaining a temperature between 150° and 158° F for one hour to convert the starch. This can be done, for example, by placing the entire pot in an oven preheated to 150° F. Remove the grain bag, and pour 1 qt. of rinse water over it and into the pot. This rinses some of the residual sugars from the grains. In a separate pot bring 3 gals. of water to a boil for at least 15 min. Add 2 of these gallons to a clean, sanitized fermenter. Keep the other gallon of water covered, in reserve. Bring the wort to a boil, and slowly but vigorously mix in the dry malt extract. Boil the wort vigorously for 15 min. and add the hops. Boil for 30 more min. Add Irish moss and boil 15 more minutes. Total boil is 60 min. Cool the wort to room temperature within 30 min. of the end of the boil. Siphon the wort off of the trub, into the fermenter, adding the reserved water as necessary to bring the final wort volume to 5.5 gals. Aerate the wort for 15 minutes. Mix the yeast starter into the wort. Seal the fermenter with an air lock, and ferment until completion.

Oatmeal Stout
5 gallons, all-grain

OG = 1.052 IBU = 35

The recipe specifies about 10 percent oats, for which a single-step infusion mash will suffice.


  • 8 lbs. pale two-row English ale malt
  • 1 lb. crystal malt, 60° Lovibond
  • 18 oz. oatmeal (quick)
  • 0.5 lb. chocolate malt
  • 0.5 lb. roasted barley
  • 1/2 tsp. Irish moss
  • 2 oz. Fuggles hops for boiling (4.2% alpha acid), for 45 min.
  • 1 pack Wyeast 1084, Irish ale yeast

Step by Step:

Prepare a yeast starter a day or two before you start your brewing. Mix the crushed grains well in a clean, dry bucket. Heat 11 qts. of water to 174° F. Mash in slowly in stages, as described below. The temperature of the mash should be between 150° and 158° F. Within this range, higher levels give a less fermentable wort and a more full-bodied beer. Lower temperatures give a more fermentable wort. Acidify 5 gals. of sparge water to a pH of 5.7 using lactic acid. Homebrewing shops sell solutions of 88 percent lactic acid concentration. A stock solution of the acid may be prepared by mixing 2 tsp. into 3 cups of water. This stock solution can be stored, and using about 1/2 cup will reduce the pH of 5 gals. of tap water to nearly 5.7. Be sure to verify this using pH papers or some other means. Acidification prevents excessive extraction of husk tannins. Heat the acidified sparge water to a temperature at or just below 170° F. Maintain the mash vessel at temperature for at least 1 hour. Mash out, raising the temperature of the mash to 168° F. To begin the sparge, slowly drain and collect 1/2 gal. wort from the lauter tun, then gently pour this back on top of the grain bed. Repeat twice more; this establishes the grain bed and produces relatively clear initial runnings of wort by filtering out any fine grain particles within the bed. Begin the sparge, maintaining the sparge water at or just below 170° F. Typically sparging for this recipes takes 45 min. to 1 hour. More time is needed if the oat content is increased. Collect 6.5 gals. of wort.

Boil the wort vigorously for 15 min. Add hops and boil 30 more min. Add Irish moss and boil 15 more minutes. Total boil is 60 min. Cool the wort to room temperature within 30 min. of the end of the boil. Siphon the wort off the trub into a sanitized fermenter. Aerate the wort for 15 min. Pitch the yeast starter. Seal the fermenter with an air lock, and let the fermentation proceed until complete.

Issue: October 1997