Malted Barley

Steeping raises the moisture of the grain in cycles of immersion and air rest — the air rests matter, because a drowned embryo suffocates. Germination then proceeds in a controlled bed, turned to prevent the rootlets matting and cooled to carry away the heat the living grain generates. The maltster is watching the acrospire, the shoot growing under the husk, because its length indexes how far modification of the endosperm has gone. Kilning then dries the green malt and halts everything.

Modification

The breakdown of endosperm cell walls and protein during germination, which makes the starch accessible. Under-modified malt yields poorly; over-modified malt has spent too much of itself.

Green malt

Germinated barley before kilning, still wet and biologically active.

Culms (malt rootlets)

The rootlets that grow during germination, removed after kilning and sold as a feed ingredient.

The kiln is where a single process becomes a product range. Dried gently at low temperature, malt stays pale and keeps its full enzyme complement — base malt, which supplies the bulk of any grist and does the converting. Taken hotter, sugars and amino acids react and the malt darkens and develops flavour, at the cost of the enzymes that heat destroys. Roasted and crystal malts, taken further still, contribute colour and flavour but little or no enzymatic activity, and are used in small proportions alongside base malt rather than on their own.

Brewing and distilling take the great majority of malt, and each has its own priorities — brewers weigh extract, colour, and flavour; malt distillers weigh extract and enzyme power and want little colour. Beyond drinks, malt goes into malt extract and malted milk, into breads and breakfast cereals, and into vinegar. The culms removed after kilning are sold into feed, so even the malthouse has its residual stream.

Malt is bought against a specification covering extract yield, enzyme activity, colour, protein and its soluble fraction, and the completeness of modification — with a homogeneity requirement, because a batch in which some grains modified fully and others hardly at all performs worse than its average suggests. Most of these outcomes are set by the barley: the maltster manages what the grain brings and cannot exceed it.

Kilned malt is drier and far more friable than the barley it came from — modification has made the endosperm crumbly, which is exactly what milling before mashing requires. That friability makes it vulnerable in handling: augering and free fall crush grains and generate fines that a brewer did not order. Malt is also strongly hygroscopic, and malt that picks up moisture loses the crispness that makes it mill properly, so it is kept dry, cool, and protected from storage insects.