Master Distiller Blog No.10 — The Three Waters of the Mash
David Hsieh
How three carefully judged water temperatures turn the starch in malted barley into fermentable sugar
By David Hsieh — Master Distiller, Tankyu Distillery | Presenter, Business Whisky Guide Podcast
Adapted from Business Whisky Guide Podcast EP10 — ‘A Right Mess of Porridge (Part I)’.
Walk into a distillery’s mash house and the first thing you meet is the mash tun — a vessel built rather like an enormous cast-iron pot. A typical mid-sized Scottish distillery runs a mash tun holding somewhere between five and twelve tonnes of grist. At its base sits a perforated plate known as the false bottom, its slots about 0.7 to 1 millimetre wide: wide enough to let the wort drain through, fine enough to hold back the husks and grist.
Inside turn two to four rake arms, shaped rather like propellers, sweeping slowly around a central spindle. Their job is to keep grist and hot water evenly mixed and free of lumps, and, during run-off, to lift the grist bed gently so the false bottom does not blind over. Some mash tuns also carry a sparger at the top, which sprinkles water evenly across the bed to rinse out the last of the sugar. Below the false bottom the sweet liquid gathers in an intermediate vessel called the underback, from which it is pumped away, cooled, and sent on to the washback to meet the yeast. The mash tun is not the elaborate piece of copper the still is, yet every dimension and placement earns its keep: the size of the false bottom’s perforations sets the speed of run-off, the rakes govern how thoroughly the mash is mixed, and the sparger decides how evenly the sugar is drawn. Get the three out of balance and the gravity and clarity of that batch of wort will suffer.
What mashing is actually for
Why does whisky-making need a mashing stage at all? Recall the malting: the barley is steeped, it germinates, and its enzymes are roused. Yet only a small part of the grain’s starch is broken down during malting; the great bulk of it survives, untouched, in the kilned malt. Mashing is the step that takes this remaining starch and, using the malt’s own enzymes, converts it into sugars the yeast can feed on. Three enzymes do most of the work: beta-amylase, alpha-amylase and limit dextrinase. Picture the structure of starch as a tree of endlessly forking branches, and each enzyme dismantles it differently: beta-amylase works like a pair of secateurs, snipping short lengths of maltose from the very tips of the branches; alpha-amylase is the axe, cutting wherever it finds a trunk; and limit dextrinase is the folding saw, going for the forks where the branches divide. Between them they reduce the starch to the single sugars (glucose) and double sugars (maltose) that yeast can use.
A narrow window of temperature
Enzymes are proteins, and like all proteins they denature with heat — much as the white of an egg turns from clear to opaque in the pan — and once denatured there is no going back. Beta-amylase begins to lose its activity at around 70°C; alpha-amylase is a little hardier, holding out to about 80°C. The opening water of the mash, then, cannot be too hot. And yet the starch itself must first be gelatinised — its granules swelling, bursting and releasing their molecules into the water — and malted barley gelatinises at around 60°C. There lies the distiller’s narrow window: too cool, and the starch never fully gelatinises, so extraction falls away; too hot, and the enzymes are lost, leaving starch the yeast can make nothing of. Years of accumulated practice have settled on a sweet spot of 63 to 65°C for that first charge of water.
Three waters, in turn
The first water carries the heaviest responsibility: it gelatinises the starch and fires the enzymes at the same time, dissolving better than seven-tenths of the fermentable sugar into the wort. The rakes turn slowly, at a middling speed, to bring grist and water fully together. After a rest of some thirty to forty-five minutes the first wort can be drawn. It is the sweetest of the three, with a gravity of roughly 1.060 to 1.075.
Once the first wort is off, a good deal of sugar still clings to the mash. So a second water follows, this time raised to 75°C — past the point at which beta-amylase gives up, but still warm enough for alpha-amylase to carry on. The hotter water rinses out the sugar held in the mash, yielding a second wort of lower gravity, around 1.020, which is cooled and fermented together with the first in the washback.
The third water is hotter still, around 85 to 90°C. At that heat even alpha-amylase has stopped working, so this water is not really part of saccharification at all; it is more of a rinse, washing the last traces of sugar from the spent grains. Because its sugar content is so low, the third wort is not sent to the washback but recovered into the hot liquor tank, to serve as the first water of the next mash. The arrangement recycles both heat and residual sugar, and is standard practice across the trade.
Variations on the theme
This pattern of three waters is adjusted by every distillery to suit its water, its maltster and the body of spirit it is after — temperatures, volumes and resting times all shift, and some houses run a fourth water altogether. The underlying skeleton, though — mash, re-extract, then a final rinse-and-recycle of the residual sugar — stays the same. Where a mash filter is used instead, as at the author’s own Tankyu Distillery or at InchDairnie in Fife, the procedure changes shape: rather than draining through the floor of a traditional mash tun, filter plates press the wort out of the mash under pressure, after which second and third waters are driven through the pressed grains to wash out the remaining sugar. Such equipment lifts extraction, shortens the mash and gives a clearer wort — though a mash filter is the more troublesome thing to clean, and asks for careful maintenance.
Mashing can look like nothing more than pouring water three times over a heap of milled malt. But, as we have seen, the temperature of those three waters, the rhythm in which they are added and the way they are recycled have already decided the character of the wort that fermentation will have to work with.
About the author
David Hsieh is master distiller at Tankyu Distillery. He has previously worked as a distiller at several whisky distilleries in Scotland. He holds an MSc in Brewing and Distilling from Heriot-Watt University, and is the host and producer of the Business Whisky Guide podcast, Taiwan's #1 whisky podcast.
About the distillery
Tankyu Distillery is one of Japan's few public-private (公設民営) craft distilleries, located in Higashikawa, Hokkaido. The company was established in 2020, and the distillery opened in August 2025. It produces single malt whisky and craft gin using pristine spring water from the Daisetsuzan mountain range — water so pure that Higashikawa remains the only municipality in Hokkaido without a municipal water supply. Learn more at tankyudistillery.jp/en.
Source
・ Business Whisky Guide podcast EP10 — ‘A Right Mess of Porridge (Part I)’.
Other distilleries, brands and producers mentioned in this article are referenced on the basis of publicly available information and the author’s personal observation, in the spirit of information-sharing rather than commercial comparison or evaluation. The references do not represent the position of Tankyu Distillery.