Just as wheat brings different qualities to a beer from barley, so it is with oats, rye and other cereals.
The extraordinary German polymath, Abbess St Hildegard of Bingen, extolled the virtues of oats in brewing as far back as the 12th century and brewers in numerous countries around the Baltic Sea historically dependent on rye for brewing.
The sweetness from oats can be more intense than from wheat, while rye can bring bring a spicy heartiness and balance out even the most assertive hopping in a way that barley does not always manage.
German Roggenbier, from a rye lager, has enjoyed a small revival in recent years and in Estonia, where brewers historically used local brown rye for centuries, every craft brewery has at least one rye beer in its portfolio, with examples that include blond and dark lagers, brown and red ales, clear and cloudy beers, barrel-aged stouts and many more.
While not strictly an alternative grain, the use of chestnut has been mastered by a few French and Italian brewers, to create rounded, sweet and nutty but earthy back tastes, offering a broad palette on which to build beers from mainstream to whacky.