Why water chemistry is the last 10% that feels like 50%

You can brew excellent beer with straight tap water. But once your process is solid, water adjustments are the easiest way to sharpen a pale ale or round out a stout. The good news is that you don’t need a chemistry degree. You need a water report, a couple of salts, and a willingness to make small, measured changes.

Start with a water report

Your water supplier publishes an annual report, usually online. Look for the ions that matter to brewers: calcium, magnesium, sodium, sulphate, chloride, and bicarbonate (or alkalinity). If you can’t find those figures, an aquarium test kit or a laboratory analysis will fill the gaps. Don’t worry about pH from the report; it changes once you add grain.

One thing to sort first: chlorine and chloramine. Half a crushed campden tablet (sodium metabisulphite) in 23 litres of brewing water will remove them almost instantly. Skip this and you risk medicinal, plastic flavours.

• Calcium: 50–150 ppm. Helps yeast flocculation and mash enzymes.
• Sulphate: 50–350 ppm. Accentuates bitterness and dry finish.
• Chloride: 50–250 ppm. Rounds malt and adds fullness.
• Alkalinity: the main driver of mash pH. Know your number.

The two workhorses: gypsum and calcium chloride

Almost every adjustment you’ll make uses one or both of these. Gypsum (calcium sulphate) adds sulphate and calcium. It makes hops pop and can give a crisp, lingering bitterness. Calcium chloride adds chloride and calcium. It softens the edges of roasted grains and makes malt taste sweeter and fuller without actually adding sugar.

Use a small digital scale, not spoons, for repeatability. As a rough guide for a 23-litre batch:

• One teaspoon (about 4 g) of gypsum adds roughly 100 ppm sulphate and 40 ppm calcium.
• One teaspoon (about 4 g) of calcium chloride adds roughly 80 ppm chloride and 45 ppm calcium.

Add them to the mash, not the boil, so they also help mash pH. Stir well.

Adjusting for style: bitter vs malty

The ratio of sulphate to chloride is your main lever. Think of it as a dial between crisp and round. For a hoppy West Coast IPA or a bitter, aim for 2:1 sulphate to chloride. For a milk stout, a porter, or a mild, aim for 1:2. For a balanced pale ale or lager, 1:1 is a safe start.

Example: your water has 50 ppm sulphate and 30 ppm chloride. For a 23-litre IPA, add 1.5 teaspoons of gypsum and 0.5 teaspoon of calcium chloride. That pushes sulphate to around 200 ppm and chloride to about 70 ppm. For a stout, reverse those amounts. Taste the difference in the first pint.

Mash pH: the quiet influencer

Alkalinity is the biggest obstacle for many UK brewers, especially in hard water areas. Your mash pH should sit between 5.2 and 5.4. Above 5.5, you get dull, harsh bitterness and poor efficiency. Below 5.0, the beer tastes thin and acidic.

Dark grains lower pH naturally, so a stout might need no acid at all. Pale malt raises pH, so a lager or pale ale often needs a nudge. If your pH is too high, add 1–2 ml of lactic acid per 10 litres of mash water, stir, and recheck after five minutes. Or use 1–2% acidulated malt in the grain bill. If your pH is too low, add a quarter teaspoon of bicarbonate of soda per 23 litres and recheck. Always measure with a calibrated pH meter—paper strips are not accurate enough.

A simple starting routine

Here’s a practical sequence for your next brew day:

• Get your water report and note sulphate, chloride, and alkalinity.
• Treat 23 litres of brewing water with half a campden tablet.
• Decide your target sulphate-to-chloride ratio. Bitter: 2:1. Malty: 1:2. Balanced: 1:1.
• Add gypsum and calcium chloride to the mash. Start with half a teaspoon of each per 23 litres, then adjust next time.
• Check mash pH 10 minutes in. Aim for 5.2–5.4.
• Take notes. Small changes, one at a time.

The same principles apply to cider making and coffee brewing. In cider, a touch of gypsum sharpens apple flavour, while calcium chloride softens acidity. In coffee, a little magnesium and calcium improves extraction, but too much sulphate makes it taste dry and papery. Water is the silent ingredient in every brew. Adjust it gently, and everything else tastes more like itself.