In the mash tun the brewer wakes up enzymes the maltster prepared. Germination, kilning and diastatic power, explained from the malthouse floor.
A drop of wort on a white plate, a drop of iodine tincture next to it. If the two turn blue-black, there is still starch in the mash; if the colour stays amber, conversion is done. Brewers repeat that little ritual every week, from Dinant to Maastricht. What it really measures is the quality of the maltster's work. In the mash tun, the brewer manufactures very little: he wakes up enzymes the malt already carries. Those invisible workers deserve a closer look.
A barley kernel is a pantry, not a factory
The starch is there, but it is locked away. A kernel of malting barley is roughly sixty percent starch, carefully packed inside cell walls and a web of protein. The plant built that reserve to feed a future seedling, not to please brewers. In the dry grain, the enzymes that could cut this starch into sugars are either absent, inactive, or trapped in the kernel's structure.
That is why nobody brews with raw barley. Throw milled raw barley into hot water and you get a cloudy porridge, hardly any sugar, and a wort that will not ferment properly. The maltster's whole craft consists of turning that locked pantry into an open one, with the tools laid out on the shelf.
Germination builds the tools
It starts with water. During steeping, the grain goes from around twelve percent moisture to over forty in about two days. The embryo wakes up and sends a hormonal signal to the aleurone layer, the thin sheet of living cells lining the inside of the kernel. That layer starts producing enzymes, in waves.
Each enzyme family has its job. Cytolytic enzymes attack the cell walls, proteolytic enzymes loosen the protein web, and the amylases deal with the starch itself. Beta-amylase was already present in the barley, but in a bound form; germination sets it free. Alpha-amylase simply does not exist in the raw kernel: it is built from scratch during those few days. This opening-up is what maltsters call "modification". A well-modified malt is a kernel whose inside crushes between two fingers like soft chalk, white and friable.
Kilning is a balancing act
Dry the grain, but do not wreck the toolbox. Enzymes are proteins, and moist heat is their worst enemy. So the maltster starts kilning with plenty of mild air that carries the water away gently; only once the grain is nearly dry does the temperature climb for the final curing. A pils malt, cured at around 80 to 85 degrees Celsius, keeps most of its enzymatic potential. A munich malt, pushed higher to develop its bread-crust notes, trades part of it for colour and flavour.
In Dinant, that heat will come from biomass. In the malthouse drum, the kilning air will be heated with hot water produced without fossil fuels, with renewable electricity covering the rest. The temperature curves themselves stay the ones maltsters have always followed: it is the drying profile that decides the fate of the enzymes, not where the heat comes from.
In the mash tun, every enzyme has its window
The brewer works with a thermometer, not a magic wand. Beta-amylase does its best work between 60 and 65 degrees: it nibbles starch chains from the ends and releases maltose, the sugar yeast likes most. Alpha-amylase, more heat-tolerant, works at around 70 to 72 degrees and cuts the chains right through the middle. Mash low and you get a dry, well-attenuated beer; mash high and longer sugars survive that yeast cannot eat, for a rounder beer.
Diastatic power puts a number on all this. On a malt analysis sheet it is given in degrees Windisch-Kolbach. A pils malt commonly shows more than 250, far beyond what it needs to convert its own starch. That margin is why the iodine test clears in twenty minutes rather than two hours.
What about the baker?
The same enzymes work in the dough. Diastatic malt flour, added at a few grams per kilo of flour, feeds the yeast extra sugars during proofing. The result: a softer crumb, a crust that browns better, a steadier fermentation, especially with flours that are poor in enzymes of their own. Roasted malts bring no active enzymes anymore, but plenty of flavour and colour, in a rye loaf or a beer bread for instance. Two uses, two malts, one logic of germinated grain.
When diastatic power matters, and when it hardly does
Let's be honest: in an all-malt beer it is rarely the limiting factor. A classic Belgian recipe built on pils or pale ale malt has a comfortable enzymatic reserve. Diastatic power becomes decisive when the brewer loads the mash with unmalted material, like the raw wheat of a witbier, oat flakes or spelt, or when specialty malts, which bring no enzymes at all, make up a large share of the grist. In those cases the base malt has to convert for two.
A number is not the whole story. An organic Belgian malt does not convert "better" than any other at equal diastatic power; what changes is freshness, batch-to-batch consistency, and the option of calling the maltster when something on an analysis sheet raises a question. That conversation is exactly what a craft malthouse makes possible.
The first malting campaign starts in mid-October in Dinant, and the first analysis sheets will follow. If you would like to see what a well-modified kernel looks like, crush it between your fingers, or simply talk mashing and diastatic power, the malthouse team will be glad to welcome you; you can reach them through mad.be.