Understanding pH
The level of pH in your mash, wort, and beer affects processes from enzyme function to hop extraction to yeast vitality. Understanding pH helps you manipulate pH levels for great-tasting beer.
But while pH is important, trying to understanding it can be a confusing affair. Your homebrew shop carries pH test strips and probably more expensive and elaborate pH meters. People talk about the pH of water, the mash, and the wort. But what is pH, what is important about it, and what do you really need to know about pH as a homebrewer?
What It Is
The term pH expresses the degree of acidity or alkalinity of a solution, in which “p” is the negative logarithm of “H,” hydrogen concentration (pH = -log[H+]). The level of pH is measured on a scale of 1 to 14, 7 being neutral, below 7 acid, and above 7 alkaline (also called basic). Because the scale uses the exponent of 10 in the logarithmic scale, a solution of pH 5, for example, will be 10 times more acidic than a solution of pH 6 and 100 times more acidic than a pH 7 solution.
Technical definitions aside, what does pH mean, in a practical sense, to the homebrewer? The pH of the mash affects the activity of enzymes and is critical for the amylases (a family enzymes) responsible for saccharification (conversion of malt starch into fermentable sugars, particularly maltose) and liquification. Different enzymes required in the mash function at different optimum pH levels, but a happy medium is achieved between pH 5.2 and 5.5. This means healthy yeast, which also perform well at a pH of about 5.5. As the yeast ferment the wort, pH drops and creates a more and more inhospitable environment for bacteria. Achieving the proper mash pH will also significantly affect hop extraction rate in the boil, facilitate proper protein precipitation, clarification of the wort, and color pick-up, and ultimately affect the flavor of the beer.
How pH Functions in Brewing
Before manipulating pH to achieve optimum levels in the mash and wort, it is wise to review some basic principles of chemistry and biology. A fundamental quality of biological systems is their ability to maintain homeostasis (stay the same). Though systems constantly exchange materials with their surroundings, they will maintain a relatively stable internal environment. The maintenance of a stable pH and resistance to sudden changes in pH is an example of this quality. Where pH is concerned, systems maintain this stability through the use of “buffers.” For example because of buffering in the human body, we are able to drink beer, which has a pH of 4 to 4.5, while our blood maintains an extremely constant pH of about 7.4.
In a solution of pure water (H2O) at neutral pH 7, some water molecules will ionize, or dissociate, into H+ ions and OH- ions. Because the water is pure, there will always be the same number of H+ and OH- ions. However, when a compound that contains H+ ions is introduced into the water, the H+ ion concentration will increase. The greater concentration of H+ ions causes the water to become more acidic, and so the pH drops. Buffers maintain a constant pH because they combine with H+ ions and either remove them from solution (as in this example) or add them back, essentially “soaking up” the acid or base. If enough acid or base is added, it will eventually overcome the buffer and the pH will rise or fall accordingly.
Malted barley contains phosphates, which are acidic buffers. Making a mash of grain mixed with water will cause the phosphate buffers to achieve a natural pH of around 5.6. Therefore, it does not matter what the initial pH of your brewing water is because the interaction between ions in water and buffering components of the malt will always change the water pH. Remember that the optimum mash pH range is between 5.2 and 5.5, so the pH of the mash needs to come down a bit to ensure complete conversion, good hop utilization, and other desirable characteristics. This is where the brewing water comes in. While the pH of the brewing water may be inconsequential, its ion concentration is of the utmost importance.
pH and Brewing Water
Being familiar with the mineral content of your water can help you achieve the proper pH in your mash. All municipal water suppliers publish a water quality or water analysis report that they will send you upon request. If you brew with well or bottled water, you should have the water tested or contact your water supplier for an analysis (read more about interpreting a water report in the sidebar on page 45). If your water supply comes from a source that has varying levels or is subject to fluctuations due to rainfall, ion concentrations may vary greatly at different times of the year.
The important ions that will affect mash pH are calcium, magnesium, and the carbonate and bicarbonate ions. These ions should be listed on your water report in either parts per million (ppm) or milligrams per liter (mg/L) — they are equal measurements. Calcium is the key ion able to overcome the buffering capacity of the malt phosphates and lower the mash pH into the acceptable 5.2 to 5.5 range. Ideal concentrations of calcium should be between 50 and 150 ppm. Magnesium acts much the same as calcium, but it is less effective at reducing mash pH. Ideal calcium concentrations, however, must be balanced with low carbonate-bicarbonate levels. Carbonate and bicarbonate ions will have a countering effect on calcium. Bicarbonates in particular are strong alkaline buffers and in large amounts will raise the pH of the mash to unacceptable levels. Carbonate and bicarbonate ions should be kept to less than 50 ppm.
The carbonate and bicarbonate ions will often be lumped together on a water report and termed “CO3.” They may not be listed separately, but they might be included under the headings for alkalinity and hardness and termed “CaCO3,” which describes alkalinity and hardness as the combined presence of calcium and the carbonate and bicarbonate ions. When you get the report you should compare the two numbers for alkalinity and hardness. If the alkalinity rating is greater than the hardness rating, you may need to remove carbonate ions from your brewing water to avoid raising the pH of the mash. If the hardness rating of the water is greater than the alkalinity rating, the ratio of calcium to the carbonate ions is probably well suited to brewing. If the two numbers are equal or are both low (less than 50 ppm) you will probably only need to add some calcium from calcium sulphate or calcium chloride back to the water to make it satisfactory for brewing.
Manipulating pH in the Homebrewery
As we have seen, ion concentration in brewing water will have a great effect on the mash pH. Type of malt is another important contributing factor. Dark malts, for instance, are naturally acidic and will overcome the buffering power of carbonate waters, dropping the pH into the correct range. For the time being let’s assume we’re brewing only pale beers.
Remember that changes to the pH of the mash, wort, or beer will be due to the addition or removal of mineral ions or the addition of organic acids. Adding mineral salts is the most common way to adjust mash pH. Mineral salts, such as gypsum, are compounds formed by a positively charged ion and a negatively charged ion. Gypsum combines the calcium ion with the sulfate ion and is an excellent source of calcium to aid in acidifying the mash. Adding one teaspoon of gypsum to 5 gallons (19 L) of water will raise the calcium level by about 60 ppm. If your brewing water is very soft (low in total minerals), you can add gypsum to raise calcium levels. If your water is high in carbonates, boiling the water for 30 minutes with calcium (either present in the water or added in the form of gypsum) will cause the calcium and carbonates to combine and precipitate out, forming a white residue in your kettle. Decant the water off the residue, leaving the carbonates (and calcium) behind. Because you’ve just removed much of the beneficial calcium as well as the detrimental carbonates, you may need to add gypsum to the water to raise calcium levels again before mashing.
If you want to brew a classic Pilsner using pale malts and soft water, you may want to employ an acid rest to ensure the pH drops to the correct range. During an acid rest, the enzyme phytase breaks phytin, a phosphate containing both calcium and magnesium that is found in the grain, down into phytic acid. In other words, phytase helps lower the mash’s pH. This is particularly important for water that has too little calcium to lower pH, such as the water of Plzen, the original home of Pilsner. The enzyme works best at temperatures between 86 and 128 °F (30 and 53 °C).
The acid rest will acidify the mash to the proper range and will also provide minerals and nutrients for the yeast. An acid rest will be unnecessary for beers made using any highly kilned malts such as crystal and dark malts and even British pale malts, because these malts will be acidic enough on their own to lower the mash pH.
The other alternative to acidifying the mash is to add lactic acid. Lactic acid blends very well with beer and will not add any unwanted flavors. You should be able to find it in your favorite homebrew shop along with instructions for use.
Again, dark malts are naturally acidic and will lower the mash pH. Even crystal malts will have some acidic effects, and the simplest solution to poor brewing water is to use a proportion of dark malts. Many great brewing centers of the world, particularly London, Dublin, and Munich, have water low in calcium and high in carbonates. The alkalinity of the water makes brewing pale ales or lagers difficult without acidification of the mash. But because they traditionally brew darker beers, such as porters, the acidity of the malt is able to overcome the buffering of the carbonate water.
pH and Sparge Water
The pH of the sparge runoff should be below pH 6. Higher pH couples with too high sparge water temperatures to extract tannins, silicates, and other undesirable compounds from the grain, which create astringent off- flavors and cloudy, hazy beer. Too high pH should not be a problem because the sparge water will mix with the mash and its pH will naturally be lowered. However, if your water supply is highly alkaline and you treated it by boiling to precipitate out calcium and carbonates for the mash, you should do the same to the sparge water. Using untreated, highly carbonate sparge water may raise the pH of the runoff above acceptable levels.
Unless you are brewing very specialized beers using undermodified malts, very pale malts, or soft water, you shouldn’t worry too much about pH. You may need to make some adjustments such as boiling or adding gypsum, but for the most part the wort will take care of itself. Expensive pH meters will give you very accurate pH readings but are probably only necessary if you are aiming for very specific results.
Measuring pH (By Chris Colby)
The best way to measure pH in a homebrewery is with an inexpensive pH meter. There are many adequate models that cost less than $100.
When you first get your pH meter, begin soaking the electrode in electrode storage solution. Whenever the meter is not in use, it will need to be stored in this solution. Ideally, the electrode should never be allowed to dry out.
Calibrate the meter according to the meter’s instructions, using a pH 7.01 buffer and a pH 4.01 buffer.
Take your wort sample in a clean glass. If the sample is from the mash, cool it down to room temperature, even if your pH meter has automatic temperature control. Taking readings of hot samples will decrease the life of the electrode. Rinse the electrode with distilled water then dry the electrode with a tissue. Don’t let the tissue touch the electrode, just bring it close enough to wick the liquid away.
Place the electrode in the sample and give the sample a quick swirl. Make sure there are no bubbles attached to the electrode. Turn on the power to the electrode. The power to the electrode should never be on unless the electrode is submerged.
With the power on the electrode, the meter will take the reading. Note it in your lab notebook, then turn the power to the electrode off before pulling it out of solution. Rinse the electrode with distilled water again, dry and return to the storage solution.
Since pH changes with temperature, you need to compensate for this change. At room temperature, the pH of the cooled sample will be around 0.35 units higher than the pH at mash temperature. Thus, if you get a reading of pH 5.60 for your cooled sample, your corrected reading would be pH 5.25. (You need to do this even if your meter has temperature correction.)
