Flaked Barley and Roasted Barley show up together in the same recipes so often — both being unmalted, both being staples of dry Irish stout — that new brewers sometimes assume they're related products at different roast levels. They aren't: Flaked Barley is barely coloured at all and contributes nothing in the way of roast character. Its job is body and foam, not colour or flavour.
Steamed and rolled, not malted
Like flaked oats and flaked wheat, Flaked Barley skips malting entirely — raw barley steamed and rolled flat, a process that gelatinises its starch mechanically so it mashes in cleanly alongside malted grain without needing a separate cereal cook. That convenience comes at the cost of any diastatic power: Flaked Barley depends completely on the rest of the grist's enzyme margin to convert.
What it actually contributes
Flaked Barley's protein content is the real story — it builds body and, in particular, contributes to a dense, persistent head, the specific creamy foam character classic dry Irish stouts are known for. That's a distinct role from Roasted Barley's dry coffee bitterness; the two work together in a traditional stout recipe precisely because they're solving different problems, not because they're variations on the same ingredient.
Colour, for comparison
At 1.3-2 °Lovibond, Flaked Barley is barely darker than a typical base malt — its colour contribution even at a meaningful percentage of the grist is close to negligible, reinforcing that its entire purpose is texture and foam rather than appearance.
Where the 20% ceiling comes from
As with any unmalted adjunct, the ceiling reflects the enzyme budget available from the rest of the grist rather than any inherent risk in the grain itself — a standard high-diastatic base malt comfortably covers a 20% flaked barley addition, and pushing further starts eating into the margin needed to convert everything reliably.
Typical use
Dry Irish stout is the defining home for Flaked Barley, almost always paired with Roasted Barley in the same recipe; it also shows up in some English milds and bitters wanting a fuller body and better head retention than an all-malt grist alone would provide, and occasionally in lighter lagers for the same reason.
Husk retained, unlike wheat or oats
Unlike flaked wheat or flaked oats, Flaked Barley keeps its barley husk through the flaking process, which means it doesn't carry the same lautering risk that husk-free adjuncts do — a mash built on flaked barley alongside a normal base malt doesn't typically need rice hulls the way a heavy wheat or rye mash would.
A wartime habit that outlasted the shortage
Flaked barley's role in British brewing has roots beyond stout specifically: during and after the World War II era, when imported adjuncts like corn and rice were harder to source in the UK, domestically grown flaked barley became a practical substitute in a range of English beer styles needing a body-and-cost adjustment. Some of that habit outlasted the shortage that created it, and flaked barley has stayed a familiar, comfortable ingredient in English brewing well beyond dry stout specifically.
Other body-builders worth weighing
Malted barley (any base malt) can approximate some of the body contribution without the specific foam-stability protein flaked barley brings; flaked oats deliver a different kind of body-and-mouthfeel boost where head retention specifically isn't the goal, and CaraPils/Carafoam is worth considering as a third option when the goal is body and foam without any of flaked barley's own grainy character.