Understanding pH
Whether in cooking or in brewing, understanding the role played by pH is indispensable and yet elusive. The pH scale measures the acidity-alkalinity continuum (i.e., the balance of hydrogen and hydroxide ions). In brewing, processes influenced by pH include enzyme activation, protein coagulation, fermentation, and even the interaction between the beer and your taste buds! These impacts are primarily affected by changing the charges of atoms in proteins, altering their shapes, and consequently their functionality. While there are many pedantic brewing topics, understanding pH really can improve the quality and consistency of your beers!
What is pH?
pH is measured on a logarithmic scale (like Richter) invented by Søren Sørensen, a brewing chemist at the Carlsberg Laboratory. Rather than a typical zero-to-infinity scale, pH 7 is defined as neutral, with numbers increasing from 7 denoting higher alkalinity (more hydroxide ions), and decreasing from 7 signifying higher acidity (more hydrogen ions) as illustrated in the chart on page 86. As this is a base-10 scale, a pH of 4.5 is 10 times more acidic than 5.5 and 100 times more so than 6.5. While 0 and 14 are often depicted as limits, there are no absolute endpoints (e.g., pure fluoroantimonic acid has a pH below -25). On the other hand, the relevant pH range for beer production is a narrow band; for non-sour beers this is 4–6, and even sour beers rarely fall below 3. The only time brewers are concerned with values outside this range it is for cleaning and sanitizing.
The characteristics of the water and malt determine the brew day pH barring intervention. The pH of the water is not significant as such, rather how minerals in the brewing liquor interact with the malt is determinative. Calcium and magnesium in the water react with phosphate from the malt to form insoluble salts, releasing hydrogen ions in the process and having an acidifying effect. Darker base malts, roasted grains, and caramel malts are themselves acidic, although there is no simple relationship between color and pH. Conversely, carbonate raises the pH by reacting with acids to form a salt and carbonic acid, which is released as carbon dioxide.
Calculators, spreadsheets, and brewing software can estimate mash pH based on your water report and grain bill, but actual measurements throughout brewing ensure accuracy. Litmus strips are difficult to read and prone to inaccuracy. ColorpHast 4.0-7.0 strips are an improvement, but readings average 0.3 lower than the correct value.1
The best solution is a suitable pH meter (cost around $100). I use a Milwaukee Instruments MW102 pH meter. You’ll also need to purchase storage solution and 7.01/4.01 buffered calibration solutions. With proper care the meter’s probe should last two years before drifting begs replacement.
The temperature of the sample will shift the pH, so I will focus this discussion on room temperature values. Even with a temperature-correcting meter, cool samples to extend probe longevity and ensure consistent readings.
Mash and Sparge
Most all-grain brewers are aware that a mash pH of 5.2–5.7 optimizes amylase activity. Luckily, the buffering capacity of the malt is usually enough to achieve an acceptable pH for starch conversion without assistance. This happy circumstance occurs because barley evolved to grow with whatever water was available. Still, hitting an ideal mash pH makes the rest of the brewing process easier.
While I understand the appeal of Five Star’s “dump-it-and-forget-it” 5.2 pH Stabilizer, in my opinion it is better to understand why the pH is high or low and then tailor your treatment accordingly. Pull a sample to measure pH five minutes after dough-in. For pale beers the ideal pH is 5.2–5.4, and for dark beers 5.4–5.6, but these targets can differ depending on your process. I employ a dilute mash (2.5 qts./lbs. or 5.2 L/kg), and consequently aim for a slightly higher pH. When I lowered a saison’s mash pH to 5.2, the amount of acid required with my hard water yielded off-flavors. While numbers are important indicators, the results in the glass are what really matter!
Fly-spargers with hard water should acidify their sparge water to a pH of 5.5–6.0 using a weak acid with buffering capacity, such as lactic or phosphoric acid. This acidification reduces the solubility of astringent husk tannins, and is especially valuable if you do not halt collection when the runnings rise above a pH of 6.0 (or below a gravity of 1.010). Batch sparging more evenly distributes the buffering capacity of the malt, but there may still be benefits to sparge acidification.
Boil
In the boil, pH regulates three important processes: Color development, protein break, and bitterness extraction. A pH drop of 0.1–0.3 is inevitable through the boil as minerals continue to react with phosphate, but some brewers encourage this by adding salts or acids.
Most of the color produced in the boil is not from caramelization, but rather the result of the Maillard reaction, a lower-temperature non-enzymatic browning process requiring amino acids in addition to sugars. The Maillard reaction happens more rapidly at higher pH values resulting in more melanoidins, which have toasty-caramel-coffee flavors and dark colors. If your goal is a whitish beer, lower the pH to 5.2 prior to the boil. Alternatively, a Scottish wee heavy or English barleywine may benefit from waiting to acidify post-boil.
The boil pH influences the amount and character of the hot break. A pH of 5.2–5.3 produces large “egg drop soup” flecks of coagulated protein. For the predominant wort proteins, a pH of 4.9 is the optimum isoelectric point, where they are least soluble, but this is usually too acidic for other considerations.
A high pH will extract more alpha acids from the hops, thus increasing utilization, but a pH in the low-5s creates a smoother bitterness by reducing tannin extraction.
Fermentation and Flavor
A pH drop is the most reliable gauge of initial yeast activity as it helps facilitate nutrient absorption. Lager strains tend to lower the pH slightly more than ale strains over the course of fermentation, but the final pH range for both is 4.1–4.7.
Beyond the influence on wort production and fermentation, the pH of the final beer itself affects perception. As one of the six (or so) tastes, sourness interacts with bitterness and sweetness. While heavy acidity and bitterness clash, a pH on the low end of the standard range increases the perception of bitterness.
While all beers are technically acidic, in most cases you want the flat beer to have a pH above 4.0, where it begins to taste sour. I target 4.4 for many recipes. However, I find refreshing saisons and wits to taste best at 4.2–4.3, while stouts and porters are less acrid and harsh at 4.5–4.6. Dry hopping raises pH, so highly-hopped IPAs can finish above 4.7 without intervention. High-pH pale beers often taste dull and flabby, the opposite of crisp and quenching. Managing the pH on brew day is usually sufficient, but post-fermentation adjustments are an option.
Adjustments
While acidity is determined by the amount of hydrogen ions present, there is no way to simply add more of them. We must choose among acids and salts that each provide additional flavors.
To lower the pH, you can start with food-grade salts to taste: Calcium chloride, magnesium sulfate (Epsom salt), and/or calcium sulfate (gypsum). The other option is subtraction, by cutting your tap water with distilled or reverse osmosis water to dilute pH-raising carbonate. If the pH is still above target for the mash or boil, add refined acid (see sidebar at the end of this story).
If you need to raise the pH, sodium bicarbonate (baking soda) is the easiest option. Excess sodium means salty beer, although 50–100 PPM can enhance malty beers. Kai Troester demonstrated that calcium carbonate (chalk) is not effective when added directly to the mash because it dissolves slowly. His solution is to dissolve the chalk in carbonated water first using a carbonator cap.3 If neither of these options are adequate, add a small amount of calcium hydroxide (i.e., slaked lime, pickling lime).
Even if you have already bottled your beer, try dosing acids or salts in the glass to evaluate the impact of a slightly lower or higher pH. Monitoring and adjusting pH isn’t flashy like adding goji berries or bacon, but it will increase your control and help you brew delicious, beautiful, and consistent beers!
Brewing Acids Sidebar
Lactic acid, also found in buttermilk, is the most traditional choice for brewing. In Germany, where the Reinheitsgebot forbid adding refined acids, wort or malt acidified by naturally occurring Lactobacillus became standard. The drawbacks to lactic acid are the precision required to measure it, and its flavor (lactate salt eventually becomes noticeable; although even 5% acidulated malt is safe2). It takes about 0.045 tsp. of 88% lactic acid per pound of malt (0.5 mL/kg) to lower the pH by 0.1. Adding 1% acidulated malt has a similar effect.
Phosphoric acid, also found in colas, is popular with brewers not bound to the Reinheitsgebot. It requires 10 times more 10% phosphoric acid than 88% lactic acid to lower the pH the same amount, demanding less measurement precision. The other advantage of phosphoric acid is that it leaves behind phosphate salts, which are relatively flavorless, and already present.
Citric acid, also found in lemons, has gained some interest for citrusy IPAs. In small-scale tests, I thought citric acid did add to the fruity perception compared to other acids. Citric acid is sold powdered for cheese making and is best added to taste at packaging. I don’t recommend acetic, malic, hydrochloric, or sulfuric acids for pH adjustment because of flavor and/or safety concerns.
Resources
1 http://braukaiser.com/wiki/index.php/An_Evaluation_of_the_suitability_of_colorpHast_strips_for_pH_measurements_in_home_brewing
2 http://braukaiser.com/wiki/index.php?title=Lactate_Taste_Threshold_experiment
3 http://www.braukaiser.com/wiki/index.php?title=Building_brewing_water_with_dissolved_chalk#How_to_dissolve_chalk_using_carbonated_water
