Gypsum

A mineral that works through water

Gypsum is calcium sulfate dihydrate, CaSO4 2H2O, a soft white mineral that dissolves slowly in water. It gives a brewery no sugar to ferment and no organism to ferment with. What it supplies is dissolved calcium and sulfate, and each gram of pure gypsum carries about 0.23 g of calcium and 0.56 g of sulfate. Its work is done in the water in which malt enzymes, hop compounds and yeast later operate, so by the time the beer is finished the powder has gone and only the ions remain.

The two waters of crystallisation in the formula are part of the solid. Calcium sulfate also exists as a hemihydrate and as an anhydrous form, and heating gypsum drives off its bound water, which is how plaster is made; wetting suitable calcined material lets it hydrate and set again. A bag sold for food use is a manufactured ingredient with a stated form, and the declared form matters because the hemihydrate, the dihydrate and a building plaster behave differently.

Gypsum is the ingredient in a German-style pils whose recipe asks for soft water with a little calcium chloride and gypsum added, with reverse-osmosis water as the starting point when tap water is hard. It also sets soybean milk into tofu. These are two very different jobs for one salt, and they share only the chemistry of calcium acting on the food around it.

From an evaporating basin to a food-grade powder

Gypsum forms where mineral-laden water evaporates and leaves crystals behind. White Sands in New Mexico shows the cycle plainly. Rain and snowmelt dissolve gypsum from the surrounding mountains and carry it into the closed Tularosa Basin, where there is no river outlet, so evaporation crystallises it again. At Lake Lucero, selenite crystals weather into the gypsum sand that makes the dunes white.

A food-grade supplier narrows the mineral to a specification. CASEA, a German gypsum producer, sells CS-Dihydrat FG as a finely milled natural dihydrate for use as the food additive calcium sulphate, E516, with no added aromas or auxiliary materials in that product. Its range also lists feed products, among them a burnt hemihydrate. Intended use decides which form is made and how it is described, and the name on the bag is the first thing to check.

Brewing gypsum in 1876

By the 1870s gypsum was already a commercial brewing product. Dingler's Polytechnisches Journal printed an advertisement from Shutes and Company of Duke Street, Derby, for gypsum specially prepared for mixing with brewing water. The firm claimed the mineral let the water extract all the alcohol-forming principles of the malt without the unwanted colour. The journal did not accept that claim, and set it against the laboratory work of the day.

The experiments pointed the other way. Frank, working after a method of Leyser, mashed malt with distilled water and with a concentrated gypsum solution. The extract recovered from 100 parts of malt dry matter fell from 70.38 to 63.23 parts in Leyser's figures and from 67.99 to 60.23 in Frank's, a loss of 7.15 and 7.76 parts. Lintner summarised the work by saying that saturated gypsum solution lowers extract yield by about 6 to 7 percent. The phosphoric acid in the wort fell as well, from 0.61 to 0.33 parts per 100 parts of extract, nearly half, and Frank connected that loss to the harm a gypsum-heavy water can do to fermentation, because yeast needs phosphoric acid.

The scale of the test matters. A saturated gypsum solution is hardly ever used as brewing water, and the article says plainly that the loss in extract is nevertheless of real importance in large-scale brewing. Other results in the same article were milder. Geisler found that gypsum did not precipitate protein out of the wort: the proteinoid figures were 4.03 parts per 100 of extract with distilled water and 4.21 with gypsum. Tauber found that 63.9 percent of the gypsum in a saturated solution mashed with malt ended up in the spent grains. Thausing brewed with water carrying 2.6 g of gypsum per litre and found the gypsum in the mash water harmless, and Lintner reported that gypsum water helped the wort to clear. Fassbender saw a faster wort break and a slower fermentation with higher gypsum contents, and no disadvantage.

Colour was part of the sales pitch, and the article measures none for gypsum. Its only remarks on wort colour concern lime and chalk, which one authority said turn wort red; Russian brewers were reported to add lime at hopping to darken their beer. The findings it reports for gypsum concern extraction, phosphate and clarification.

The debate is useful because it separates an effect from an explanation. Adding a salt changes several things at once, and the brewer sees only an extract, a fermentation and a flavour. The 1876 authors argued over which comparison showed what, and over whether a concentrated laboratory solution said anything about the water in an ordinary brewhouse.

Calcium, sulfate and the mash

Dissolved gypsum brings calcium and sulfate together, and they do different jobs. In the mash, calcium reacts with phosphates from the malt, which releases hydrogen ions and lowers the pH; bicarbonate in the water works the other way and consumes acidity. The malt supplies its own buffering substances and acids, so mash pH is the outcome of the water, the grist and any treatment together. The target is a mash pH of 5.1 to 5.5, and calcium is described as essential for reaching it. Calcium also keeps oxalate in solution, reduces tannin extraction and helps proteins coagulate in the hot and cold breaks, and it supports malt enzymes. Gypsum does not carry a fixed pH correction that works for every batch.

Sulfate has a different effect, on taste. At high concentrations it accents hop bitterness and dryness, and the brewing world's favourite example is the water of Burton-on-Trent, the English town whose pale ales made its wells famous. Its water carries about 352 ppm of calcium and 820 ppm of sulfate. Brewers elsewhere add gypsum, together with Epsom salts, to bring their water towards Burton levels, a practice called Burtonising. The dry impression that sulfate gives is a sensory effect, not extra fermentation: attenuation, the amount of sugar the yeast consumes, and the perception of bitterness are separate matters.

Pilsen sits at the opposite end. The water of the Czech city that gave pilsner its name has about 10 ppm of calcium and 4 ppm of sulfate, with almost no bicarbonate, and a mellow hop bitterness is the result. A brewer making a pale lager from soft water adds a little calcium to bring the mash into range, and gypsum is one of two salts that can do it; calcium chloride is the other, and it adds chloride, which enhances the perception of sweetness at low concentration, in place of sulfate.

In the water of a German pils

A modern pils recipe is a designed formulation, not a sample from an old well. Water treatment lets a brewer start from soft or reverse-osmosis water and build the mineral profile wanted, and the recipe in this entry takes exactly that route, adding calcium chloride and gypsum to soft water. The salts serve two purposes together: calcium for the mash and sulfate in measured amounts for the hop character of a crisp lager. The quantities depend on the starting water, which is why brewers analyse it before they adjust it.

Using two calcium salts gives the brewer two ways to tilt the same mash. Both supply calcium, but gypsum adds sulfate, which sharpens hop bitterness and dryness, while calcium chloride adds chloride, which enhances the perception of sweetness at low concentrations and, at high levels, can hamper yeast flocculation. Yeast also needs magnesium, 10 to 20 ppm of it, and more than that tastes harsh and mineral. A balanced pale lager water keeps all of these low and deliberate, which is why the starting point is soft water rather than a hard tap supply.

The useful way to think about a water addition is to begin with the water. The same gram of gypsum in a litre of Pilsen water and in a litre of Burton water gives very different results, because the calcium, sulfate and bicarbonate already there decide where the additions land.

Gypsum in tofu

Calcium sulfate is also a classic coagulant for soybean curd. Here it acts on soy proteins, not on a mash. Tofu making begins with soybeans soaked for 9 to 10 hours at 22 degrees C (or 4 to 6 hours at 32 degrees C), ground and cooked as a slurry at 100 to 110 degrees C for 3 to 10 minutes, which denatures the protein and drives off beany volatiles. The soymilk is separated from the okara, the solid pulp, and is coagulated at 60 to 90 degrees C with a coagulant at 1.5 to 5.0 g per kg, with a little stirring at the start. Calcium ions then bind and bridge the soy proteins into a gel, which is pressed for firm and extra-firm tofu.

Gypsum is the most traditional of the salt coagulants, and it does not mask the flavour of the bean. Nigari, a mixture of magnesium and calcium chlorides, is more soluble and gives a smoother tofu, but its composition varies, which complicates large-scale production. Glucono-delta-lactone, an acid-forming coagulant, sets so quickly that silken and soft tofu can coagulate inside their own package, with a slight sourness. Calcium sulfate used together with it gives soft, smooth tofu. The solids content of the soymilk largely decides the final texture.

J. M. deMan, L. deMan and S. Gupta compared five coagulants in 1986: calcium chloride, magnesium chloride, calcium sulfate, magnesium sulfate and glucono-delta-lactone. Calcium chloride and magnesium chloride set the milk quickly and gave coarse, granular, hard curds. Calcium sulfate, glucono-delta-lactone and magnesium sulfate worked more slowly, and the curd from calcium sulfate was smooth, soft and uniform. Concentration mattered as much as the coagulant: 0.75 percent calcium sulfate was the most suitable for tofu of high bulk weight and smooth texture. The calcium sulfate in that study was the hemihydrate, and the dihydrate sold as food-grade gypsum is a different form.

Texture is the culinary consequence. A soft, uniform curd and a hard, granular one eat differently and stand up differently in a dish, which is why tofu makers treat the coagulant as a decision about eating quality and not only about yield.

Choosing and handling gypsum

For food use the checks are a declared food-grade designation, a stated calcium sulfate form and the product specification. A retail tofu-making supplier sells fine white food-grade calcium sulphate powder in small packs, and its photograph shows what the dry ingredient looks like, a powder where a mineral specimen would be a lump of crystal and a block of curd would be wet and soft.

As a pure mineral salt it carries no protein, and the CASEA food grade lists no aromas or auxiliary materials; a blended product should be read against its own declaration for carriers or anti-caking agents. Gypsum for brewing, for tofu and for animal feed come from different specifications, and the food specification is the one that matters in a kitchen.