Article

The Role of pH in Brewing

Many years ago I said to a fellow brewer, “You know, the more I learn about brewing, the more I realize I know nothing about brewing.” To which he responded, “That will never change.” Being as how he had many more years in the business than I, it let me know that brewing is a long mystifying road. Joys of resolving problems, frustrations of bewilderment, and of course tasting the fruits of our labor keep us coming back for more. Understanding pH is just one small piece of the brewing puzzle — but a very important piece that can take our beer from okay to great. Grain to glass, the observation of pH throughout every part of the brewing process will help us understand this wonderful beverage a little more.

Mash pH

All pH samples, in the mash tun or otherwise, should be taken at room temperature. Even with the technology of ATC (automatic temperature control) this will only compensate for the probe and not for the shift that chemically happens during temperature differences. ATC does not work the same as CTC (conductive temperature compensation). At higher temperatures it is easier for the splitting of hydrogen protons from molecules. Therefore, at higher temperatures there can be readings of lower pH. All pH readings  should be taken at room temperature for sake of consistency.1

There are many enzymes at work in our mash tun. Because not all of them are at peak performance at the same target pH, not all brewers and scientists can settle on ideal range (Palmer: 5.2–5.8, Noonan: 5.2–5.5, Narziss: 5.4–5.6, Fix: 5.2–5.6). However, it is generally agreed that a pH in the realm of 5.2–5.8 is adequate. Malt has tremendous buffering power to get roughly in this target mash pH area when mixed with water.

pH affects many aspects of our mash including yield of extract, fermentability of sugars, polyphenol extraction, protein degradation, saccharification rest time, and lauterability. Most of these rely on enzymatic activity. We need to keep these enzymes happy so they can do their work for us. The interaction of the amino acids that constitute an enzyme are dependent on their electrostatic charge and pH greatly affects these charges. Outside the correct pH range the binding of the enzyme to its substrate cannot occur, rendering the enzyme useless. This will only occur in extreme cases and is difficult to achieve in the mash. So long as the pH is within 2 pH units, the enzymes are not permanently deactivated and can usually be corrected.

It is important to be able to control the degradation of proteins, beta-glucans, and starches during the entire brewing process. The measurement of pH will help us get a grasp on such a task. Having a pH lower than 5.2 increases the probability of solubilizing proteins into the wort that would later have come out during the boil or cold-crashing. This will increase the possibility of haze in the finished product. Having a pH above 5.8 can extract tannins from the grain, giving the beer a harsh astringent taste. Studies by Macwilliam (1975) and Taylor (1990) found that an increase in pH will reflect a decrease in carbohydrate yield.2 As it pertains to extract yield, an infusion at the pH of 5.2–5.4 has the most positive impact.

Often, the need of calcium or acid, (be it in the form of acidulated malt, phosphoric, or lactic) is needed to lower the mash pH. Roughly 1.5 mL per liter of 10% phosphoric acid, (or for large scale commercial batches, 7 mL/bbl of 85% phosphoric acid) will drop the mash pH by 0.1. If using salt additions, 305 mg of CaCl2 or 358 mg CaSO4 per liter  will reduce mash pH by 0.1.3

Lauter pH

Enzymatic activity is typically complete after our mash rests. Assuming we have reached mash out temperature (170 °F/77 °C), we have significantly increased the denaturing rate of our enzymes that convert starch to sugar, fermentable or otherwise.

At Rohrbach Brewing Co., where I am a brewer, we do not typically treat our sparge water. The natural high pH of water helps stimulate extraction during lautering.2 As water is added in its natural element, the pH of the wort will increase. Therefore, it is important to start on the lower end of the mash pH spectrum. Grain bed permeability is greatly increased at a lower pH of 5.2 as compared to 5.8, increasing ease of wort transfer from the lauter tun.2 The more wort that is run from the lauter tun, the more polyphenol extraction will occur during the final stages. At this point the pH will rise.

It is important to stop collecting wort when the pH of the final runnings climb into the 5.8–6.0 range as it will start to give the wort a harsh bitterness and astringency due to the extraction of polyphenols from the malt husk. Take a pH reading during vorlauf. As you are running off, monitor the pH by taking samples and chilling them down to room temperature for a proper pH reading every 20 minutes. Increase the rate in which you take these readings to every few minutes during the last 10 minutes of run-off. Example: If you have planned on a 1-hour run-off, take a reading at 20, 40, 50, 53, 56, and 59 minutes. When collecting samples you can chill them down on ice or in a freezer. I recommend using borosilicate glass for these samples as it is more resistant to thermal shock.

It can be difficult to chill samples and take pH readings while still cutting off the sparge in time to avoid over extraction. There are methods some have adopted such as taking readings at high temperatures and subtracting 0.35 to get what could be possibly the right reading. Due to the different variables stated previously and potential damage to the meter probe, I do not recommend this strategy. I have adopted the trials method of continually keeping track of pH and reviewing the data. The more attention you give to pH and gravity readings during run-off, the more of an understanding you will have of the trajectory.

Kettle pH

The same mechanisms that increase tannin solubility in the mash and boil at a high pH will also increase the solubility of hop resins during the boil. Hop resins are acidic and during the boil at a high pH will lose hydrogen ions. This instability creates an increase of solubility in the wort.4

Alpha acid solubility depends primarily on two things: Temperature and pH. The boil temperature is largely constant, but the pH of the wort may fluctuate. According to a study done by Dennis Briggs in 2004, an increased pH will lead to an increase in solubility of alpha acids (A chart illustrating this point can be found online by searching “hop solubility chart.” There are many claims, however, that bitterness extraction in a more basic element comes across as harsh and rough, as compared to a smoother more pleasant bitterness at a lower pH.4

Regardless of the pH at the beginning of the boil, it will become more acidic the longer it is boiled. This is for a couple of reasons. During the boil there will be precipitation of calcium by way of phosphates. Calcium from the water or salt additions will bind with the phosphates of the malt to form calcium phosphate and excess hydrogen ions. The calcium will precipitate out of solution and the hydrogen ions will stay behind, in turn, lowering the pH.5 It can therefore be important to add calcium during the mash knowing that this shift will happen. If the mash pH is at target but the post-boil pH is not less than 5.4 it can be beneficial to add calcium salts to the kettle as well.

Another reason for drop in pH during the boil is due to formation of melanoidins through the Maillard reaction. Amino acids such as glutamic and aspartic acid are highly reactive during the Maillard reaction. Because of this, the development of melanoidins during the boil will decrease the pH of the wort.6 The drop in this pH is beneficial to precipitation of proteins and polyphenols. Unlike the mash, a lower pH during the boil will help minimize turbidity. As previously mentioned, a mash pH of less than 5.2 will solubilize proteins into the wort. At a kettle pH of less than 5.2 you will see the coagulation of these proteins.This will have an impact on clarity, yeast harvesting, and filtering.

Kettle fining agents such as Irish moss and Whirlfloc are made from carrageenan, which is a type of seaweed. At a kettle pH of 5–5.7 many proteins carry a negative charge. Conversely, these agents carry a positive charge. When adding these carrageenan-based agents to the boil they attract the proteins that can cause haze.

Fermentation

The pH will continue to decrease after the kettle. This decrease will aid in more precipitation and coagulation of proteins that will drop out of suspension and can be discarded with cold-side trub. Low molecular weight albumins will adhere to yeast cells and flocculate out with them.7

When the yeast cell deviates from its optimal functioning pH range (5.0–4.3), they can become sluggish and slow the reduction of off flavors acetaldehyde (green apple) and diacetyl (butter) during maturation. The production of these are normal in the early stages of fermentation but given the proper conditions they will convert them. The diacetyl will be reabsorbed and enzymatically transformed into the essentially flavorless compounds acetoin and 2,3-butanediol. While these compounds have a similar flavor to diacetyl, the flavor threshold of them is much higher, making it difficult for the palate to detect. The vast majority of acetaldehyde will be converted to alcohol, bringing the concentration below the flavor threshold.

The yeast will need to invest energy in pumping in or out hydrogen ions to maintain optimal intracellular pH. In doing so, the cells may excrete glycogen. Glycogen is a more complex branched version of amylopectin. It has more α-1-6 bonds than starch and may cause chill haze in the final product.7 In addition to producing these off flavors and clarity issues, a pH that is too high will also hinder the yeast to clean up these by-products. It will slow the reduction of diacetyl and acetaldehyde, and foster the production of higher molecular weight fusel alcohols.8

Like malt, yeast too has tremendous buffering capability, though it is important to give it the best chance possible. In some respect, it is best to be on the lower side during fermentation. Aside from inhibiting some bacterial growth, a lower pH makes for ease of filtration. If using gelatin or isinglass fining agents, a low pH beer will enhance the ability of the positively charged material to bind with the negatively charged yeast and flocculate to the bottom of the fermentation vessel.

Fermenter fining agents such as isinglass and gelatin behave differently than kettle finings. Most proteins at the <5 pH of fermented beer are positively charged and while these collagen-related fining agents have no effect on these ions, they do have an effect on protein-tannin reaction. Often, haze found in beer is not the cause of protein alone but from proteins bonding with tannins. It is tannins that these fining agents bind with and flocculate, bringing the proteins with.

Though there are mechanisms that increase hop-resin solubility on the hot-side production, a reduction in solubility of alpha acids can be seen during fermentation. As the pH falls, these alpha acid compounds will adhere to matter and will float to the top as kräusen or to the bottom as trub.4 If a smooth bitterness is desired, this should be removed by skimming, utilizing a blow off tube, and/or dumping from the bottom of the tank.6

A final pH should be taken after the beer has been crashed and all yeast and trub has been discarded as to make sure there is little deviation from the final day of fermentation. Yeast autolysis will raise the pH. A target pH of ~4.4 is good for most styles. Above 4.6 in finished beer will enhance chalk/alkaline components and the beer will come off as cloying.

Flavor

Even by the time the beer reaches our glasses our concern for proper pH is not over. pH affects flavor perception in a big way. A high pH can make beer seem dull while a lower pH can make it seem more refreshing and crisp. For most craft beer that range is between 4.3 and 4.6 for an uncarbonated sample. Adjunct beers can sometimes be lower because they lack the buffering capacity that all-malt beers do. I have personally taken pH samples of a very popular adjunct ale that was 3.9. Sour beers, of course will have a pH much lower.

References

1 Martin Brungard PE. D. “Water Chemistry. ” Bru’n Water
2 Fix and Fix. “An Analysis of Brewing Techniques”
3 “Low-Tech Mash.” Master Brewers Association of the Americas Brewing.
4 Kunze, Narziss. “How pH Affects Brewing.” Braukaiser Online Index
5 John Palmer and Colin Kaminski. “Water; A Comprehensive Guide for Brewers.” Brewers Publications
6 Wolfgang Kunze. “Technology Brewing and Malting” 3rd edition
7 Elisabeth Steiner, Thomas Becker, Martina Gastl “Turbidity and Haze Formation in Beer” Journal of The Institute of Brewing
8 Chris White and Jamil Zainasheff. “Yeast; A Practical Guide to Beer Fermentation.” Brewers Publications

Issue: December 2018