Ideas filter into brewing all the time. Most of the time, new ideas simply fall by the wayside. Others enjoy a brief moment of popularity before fading into obscurity. A very few are tested through the experience of brewers, show that they make a positive difference and become a permanent part of the way we brew. One new idea in homebrewing is that you should acidify your sparge water. I will argue that, for most homebrewers, this is not accomplishing anything worthwhile.
The idea behind acidifying your sparge water is straightforward. When you mash, you want the pH to fall into a range (5.2–5.6) that favors the action of the amylase enzymes. As you collect the wort and begin sparging, the pH of the runoff wort will start rising. If it rises above a pH of 5.8, excessive tannins (and silicates) will be extracted from the grain husks, leading to astringency in your beer. The idea behind sparge water acidification is to add acid to your sparge water to prevent the pH of your final runnings from rising above 5.8, and thus prevent your beer from being astringent. I have read from one prominent homebrew author and heard from another that a pH of 5.5 in your sparge water is desirable.
That’s the Facts, Jack. But . . .
You’ve probably heard the saying, “A little knowledge is a dangerous thing,” and I think that applies here. But let’s start by acknowledging that each little piece of the above argument above is true. You do want your mash to fall into a reasonable range (and 5.2–5.6 is the oft-quoted range); you don’t want the pH of your final runnings to exceed 5.8 (because excessive tannins will be extracted) and adding acid to sparge water does lower its pH. However, let’s take a look at what this argument is ignoring.
A Closer Look
There are at least three things I will argue should also be looked at. The first is that the two acids most commonly used in homebrewing — lactic acid and phosphoric acid — have a flavor to them. If you add them to your sparge water, you may be adding a hint of their flavor to your beer. (Not that this altogether a horrible thing. Lactic acid is normally present in beer and is the most common acid in sour beer. Likewise, if you’ve ever drank a Coke, the taste of phosphoric acid is part of its flavor profile. Neither of these acids tastes inherently terrible. However, their flavor may not be appropriate or welcome in some styles of beer.)
The second thing to consider is that most homebrewers likely never reach the point in wort collection when their pH climbs above 5.8. In order to get to that point, you need to sparge until the specific gravity of your final runnings is quite low. How low would depend on your water chemistry and lautering speed, but probably 2 to 3 °Plato (SG 1.008 to 1.012) in most cases. Given that most homebrewers collect only as much wort as they can boil down in 60 or 90 minutes, they likely don’t reach that point, especially for higher-gravity beers. (The possibility of this occurring increases if the brewer brews a low-gravity beer and still collects enough wort for a full-wort boil. Likewise, brewers with carbonate-rich water may reach this point sooner than brewers with less carbonates in their water.)
The third, and by far most important, thing to consider is that most homebrew does not suffer from being overly astringent. To me, acidifying your sparge water is a solution to a problem that doesn’t exist. Beer has been brewed for centuries without doing this. None of the professional brewing texts I have mention this. (In Germany, while the Reinheitsgebot was in effect, this would not even have been permitted. Incidentally, German brewers sometimes used to late runnings from one beer as part of the mash liquor for the next brew.) If you regularly brew overly astringent beers, adding acid to your sparge water may help. But if you don’t have a problem with astringency, why bother?
Flogging a Dead Horse
For those with a chemistry background, there’s one other way to look at this. Early during the runoff, when your wort is still at or near mash pH, the wort is not only acidic enough to prevent excessive tannins from being extracted, it is also fairly heavily buffered. (A buffer is a substance that resists pH change in a solution, and first wort has plenty of amino acids and other substances to buffer it.) Any acid in your sparge water is not doing much of anything at this point except lowering the buffering capacity slightly. The same amount of acid it would take to lower your sparge water from a pH of 7 to a pH of 5.5 is not enough to change your mash pH appreciably. (It would, however, slow the rise in pH towards 5.8 when collecting wort.) As you collect wort, the amount of dissolved solids (including sugars, acids and buffers) in it decreases and the pH rises. It’s only at the point that the pH of the final runnings climb above 5.8 (or slightly before) that acidifying the sparge water would begin to help. And at that point, almost all of the sugars have been rinsed from the grain bed.
If you routinely sparge your grain bed until your final runnings are very dilute, or if you frequently yield overly astringent beers, acidifying your sparge water may be worth considering. (I would argue that collecting less work would be a better solution, but your mileage may vary.) If your beers are not unpleasantly astringent, then adding acid is at best not helping and at worst may add some unwanted flavor to your beer.
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