Beer is an agricultural product

Barley, and why it rather than anything else

Barley became the brewing grain for reasons that are practical rather than traditional. It has a husk, which forms a natural filter bed during lautering — wheat and rye, which lack one, are difficult to run off and are usually blended with barley for that reason alone. It has high enzyme potential, so it can convert its own starch and some borrowed from other grains. And it is not the primary bread grain in most of Europe, so brewing it was less likely to compete with feeding people.

Malting barley is a specification crop rather than a commodity. It is grown to contract, tested for protein, germination energy and screenings, and rejected for malting if it misses — at which point it is sold as animal feed for considerably less. Protein is the critical number: too high and the beer is hazy and the extract poor, too low and there is not enough for head retention and yeast nutrition.

A grower is therefore aiming at a narrow band, in a crop whose protein depends on weather they do not control. That is a large part of why malting barley trades at a premium and why a bad season is felt through the whole chain.

What the maltster does

Malting is a controlled germination. Grain is steeped until it takes up water, allowed to germinate for several days so enzymes develop and the starch reserves begin to break down, and then dried in a kiln to stop the process at the chosen point. Everything about a malt — its enzyme content, how completely its starch is accessible, its colour and its flavour — is set in those few days.

The kiln is where colour is decided, and that is a comparatively recent power. Malt dried over a direct fire takes smoke and colour from it, which is why all old beer was brown and faintly smoky; indirect kilning made pale malt possible and turned colour into a choice. Roasting at high temperature in a closed drum, patented in 1817, made intensely dark malts available in small proportions.

Most breweries do not malt. It is a separate industry with its own economics, and the handful of breweries that still operate their own maltings — two in Bamberg smoke their own — are notable precisely because it is unusual.

The other grains, and why they are there

Wheat contributes protein for head retention and a particular soft texture, and is essential to whole style families. Oats contribute beta-glucans that give a silky body, which is why they are in stouts and modern hazy IPAs for opposite-seeming reasons. Rye contributes a distinctive spiciness and is difficult to work with.

Maize and rice are the ones that attract argument, and the argument is usually conducted without the history. Both are used as adjuncts because they contribute fermentable sugar with very little protein or flavour, which lightens body and colour. American brewers adopted them in the nineteenth century because North American six-row barley is high in protein and needed diluting — a technical solution to a local crop, not a cost-cutting exercise, though they are certainly also cheaper.

And the part that is not agriculture

Water is the ingredient a brewery has most control over and historically had least. Local water chemistry genuinely constrained what a town could brew well — Burton's sulphate suits pale hoppy beer, London and Munich's carbonate suits dark malt — and that correlation is real.

The causation is more contingent than it is usually told, and it is now largely historical. Modern brewers strip water to a neutral base and rebuild it, so a brewery in any city can make a convincing pilsner or a convincing stout. Water explains why particular styles arose where they did; it does not constrain anybody today.