Many all-grain brewers take pains to adjust the mineral content of their water when brewing different beers. Brewing a stout calls for water with a healthy dose of carbonates to counteract the acidity of the dark grains. For a light Pilsner, little or no carbonates, but plenty of calcium to help the mash pH drop into the right range.
In the past, advice on water treatment for extract brewers has been all over the board. Some sources claimed your best bet was to mimic the water profile of the city the beer style originated in — and to this day you can still buy “Burton salts” in many homebrew shops. Other sources claimed that the mineral content of the water was irrelevant. Still others claimed that most water types were OK, but distilled or reverse osmosis (RO) should be avoided because yeast require minerals to thrive.
In reality, the water treatment plan for an extract brewer is very simple in most cases. You can understand this best by understanding what malt extract is. Brewery grade malt extract is post-boil wort that has been condensed or dried. The extract manufacturer has mashed malted grains, ran off the wort and boiled it. Then, the wort is processed to remove water, leaving either liquid malt extract syrup or dried malt extract powder.
All-grain brewers typically treat their water to cause their mash pH to fall within the proper range (5.2–5.6). Some may additionally add a pinch of calcium to the boil, to help the wort reach the proper post-boil pH (5.0–5.2). For malt extract brewers, both of these objectives have been met in the manufacture of the extract. The pH of the prospective beer still needs to drop during fermentation (to 4.0–4.4), but the water you use to reconstitute your malt extract will have little effect on this. (If you have “extra chunky” water — very hard water with loads of carbonates in it (over 300 ppm), you may want to dilute your water a bit with distilled or RO water, just to be on the safe side.)
Dissolving Malt Extract
So, from the viewpoint of reconstituting your malt extract — and ignoring for the moment the contributions of steeped grains or wort from a partial mash — the mineral content in your water matters little. Using distilled or RO is fine as your reconstituted wort will retain the minerals from the original wort. Likewise, adding minerals to mimic Burton water — or to match the water profile of an all-grain recipe — isn’t going to hurt (as long as you keep your additions within reason), but it isn’t accomplishing what it accomplished in the all-grain beer.
In almost every case, using your tap water — either carbon filtered or treated with one Campden tablet per 20 gallons (76 L) to remove chloramines — will work fine when making an extract beer. If your water tastes good, you can make good beer from it. Adding small amounts of mineral salts or “cutting” hard water with distilled or RO water to remove them will have little impact when it comes to your fermentation.
Of course, most malt extract brewers don’t make beer solely from reconstituted malt extract. They also flavor their wort with steeped grains or with the wort from a partial mash. And here’s where things get a bit trickier, depending. If you are performing a partial mash, your water considerations are the same as if you were an all-grain brewer with a full mash. Adding base malts improves the aroma of extract beers, but you will eventually want to learn a little about water chemistry if you do. For starters, though, the improvement in flavor and aroma should be enough of an incentive. (In many cases, if not most, a partial mash will work well enough even if you use plain tap water don’t muck with your water chemistry. So don’t be afraid to jump in and try it.)
If you are simply steeping grains — such as crystal malt or dark malts such as chocolate malt or black malt — however, your water requirements are very lenient. When steeping grains, you don’t have to be concerned with the pH of the “grain tea” as you are simply dissolving sugars from the interior of the grains and flavors from the husks. Again, using any water that tastes good and has been treated to remove chlorine will accomplish this.
If you are brewing a hoppy beer, adding a little gypsum (calcium sulfate) can accentuate the hop character. If you know that your water is low in sulfates, you can add gypsum to yield up to 250 ppm of sulfate ions to accentuate the hops. If you don’t know how much sulfate is in your water, your best best bet would to either omit any addition of gypsum, or add only a small amount (1 tsp. per 5 gallons (19 L), which adds about 50 ppm) the first time you brew the beer and see how your beer turns out. You don’t need tons of gypsum in your wort to make a tasty hoppy beer.
So, when making your wort from dissolved malt extract flavored with steeping grains, the main requirement of your water is to not interfere with the pH drop in fermentation. Also, it should not contain so much of any particular mineral as to cause flavor problems. Given this, the tap water from almost any municipal source will be fine (as long as it tastes good and you’ve treated it to remove chlorine compounds). If your water is exceedingly high in carbonates (over 300 ppm), diluting it below this level with some distilled or RO water might be a smart pre-cautionary manner. Avoiding large mineral additions called for in an extract recipe (over 2 tsp. of salts) is also a good bet. Your tap water is probably fine on it’s own, but all bets are off when you start adding things willy nilly. (Get a local water report and know what’s in your water before trying to modify it.)
If you brew partial mash recipes, or convert your extract recipes to partial mash formulations, you will benefit from learning about water chemistry and treating the water used for partial mashing and sparging the partial mash (rinsing the grains), However, a lot of all-grain brewers started out by simply using their tap water and this frequently works well enough.