Measuring Mash pH, Wort Aeration, and Beer In A Bag

Q I like to brew well-hopped English-style IPAs. Do I check the pH before or after the addition of grains? What pH am I aiming for and what is the best method to achieve the desired result?

Chris Bennett
Alfreton, England

A Questions about pH and its relationship to brewing are very deep. So deep in fact, that the pH scale was developed and introduced to the world in 1909 by Søren Peter Lauritz Sørensen, head of the Carlsberg Brewing Laboratory in Copenhagen, Denmark from 1901 to 1938. Maltsters and brewers keep a careful watch on pH because of its influence on all biochemical reactions. Just a shallow scratch of the surface of this topic reveals malt color, enzymatic activity during mashing, color development and hop utilization during wort boiling, trub behavior in the whirlpool, microbial activity in unpitched wort and in fermented beer, and oxidative and colloidal stability of packaged beer, as examples of the myriad aspects of how beer is touched by pH. What follows will not be a rambling journey down this interesting rabbit hole!

Before or After?

I have been spending much more time checking out homebrewing social media since life as we all knew it changed in early 2020. The question about when to adjust pH is perhaps one of the most common questions about this topic. I see my friend and fellow BYO contributor, Denny Conn, frequently posting short quips about this question. The answer is simple; check mash pH after malt is added and the mash is allowed to settle for a bit. A bit? Yeah, more on that in a bit.

Photo courstesy of

Without getting bogged down into the specifics, the pH of brewing water tells a very incomplete story because there are three components in water that have a profound effect on mash pH (calcium, carbonate/bicarbonate, and magnesium), yet only one of the three, carbonate/bicarbonate, affects water pH. And that effect is not simple because carbonate/bicarbonate is a buffer system that opens up a chapter in organic chemistry titled “Buffers, Buffering Capacity, and the Henderson-Hasselbalch Equation.” Suffice to say, water pH is not very useful to brewers because mash pH is affected by stuff in water AND stuff in malt.

When does a brewer measure mash pH? A little bit after mashing in, of course! Proteins, polypeptides, phosphates, and other organic molecules with carboxylic acid moieties react with calcium and magnesium and release protons into the mash; this lowers pH. The carbonate/bicarbonate buffer system is also busy doing its thing, which typically results in mash pH being pushed upwards. Since these reactions do not happen immediately upon mash-in, some time is required for the mash pH to stabilize. Like so many things in brewing, there is no magic time required for pH to stabilize; 15 minutes is usually long enough, but pH usually stabilizes after about 5–10 minutes. In the vernacular of non-specific direction, seasoned brewers say, “wait a bit after mashing in to check mash pH.”

Let’s assume we have mashed in for a nice hoppy, English-style IPA. The recipe is classic: 80% Golden Promise malt, 15% torrefied maize (a.k.a. corn), and 5% medium crystal malt. We wait for 15 minutes, and pull a mash sample. Now what? Well if the brewer is practical, they may have a pH meter with an electrode that doesn’t mind hot measurements and the mash pH is measured. Others will cool the mash to 68 °C (20 °C) before a measurement is taken. So, 15–25 minutes later, we have our pH value. Drats! We discover that our pH is 5.6 and we really wanted pH 5.4. Does the practical brewer add acid? Well, that depends on the practical brewer. This practical brewer would make a note in the brewing log, play with the sample by determining how much acid would be required to adjust the pH, and use this information on the next brew. The problem that many homebrewers have is that the next brew may be an entirely different type of beer.

Suffice to say, water pH is not very useful to brewers because mash pH is affected by stuff in water AND stuff in malt.

Target pH is another one of those things that depends on what you are aiming to do. The general rule is to have a pH in the 5.4–5.6 range (measured at 68 °F/20 °C).

Adjusting Mash pH

The three most common methods used to adjust mash pH are through water salt additions, for example, by adding gypsum (calcium sulfate) to your brewing water before the mash, malt selection, and acid additions. Your question was thankfully simple in that you asked for the methods, not a deep dive into the chemistry behind the method. Basic calculations are, however, required to estimate mash pH. Here is a method for estimating mash pH:

Estimated Mash pH = (wort pH from malt COA) + (RA x 0.03) – (% crystal malt x 0.025) – (% lightly roasted malts x 0.03) – (% darkly roasted malts x 0.05) – (% acidulated malt x 0.01).

Residual Alkalinity (RA) = (ppm carbonate/bicarbonate in water x 0.046) – (ppm calcium in water x 0.04) – (ppm magnesium in water x 0.03).

And here is an example:
Assume the grist bill is 95% base malt and 5% crystal malt (note this method does not have a spot for adjunct grains), and the water contains 60 ppm carbonate/bicarbonate, 120 ppm calcium, and 20 ppm magnesium. You need to check a “COA” (certificate of analysis) of the base malt used for this brew. That information is not always easy to find, but for this malt let’s assume we know that the value is pH 5.9 at 68 °F (20 °C).

RA = (60 x 0.046) – (120 x 0.04) – (20 x 0.033) = -2.70

Estimated Mash pH = (5.9) + (-2.70 x 0.03) – (5 x 0.025) = 5.7 at 68 °F/20 °C

In the example above, the predicted mash pH is higher than the target. The options for mash pH adjustment are water chemistry, tweaking the grist bill, and adding acid. The equations above show the basics on using water and malt selection to adjust pH. What about adding acids? Definitely an effective, relatively easy, and common method, with lactic and phosphoric acids the most common food-grade acids used by brewers.

The general rules for these acids are that 0.66 grams of either 88% lactic acid or 85% phosphoric acid added to 1 kg (2.2 lbs.) of grist (“normal” mash thickness in the 3 liters water per kg malt is assumed) will reduce mash pH by 0.1 pH units. For my non-metric friends, this translates to 0.01 ounces of acid per pound of malt in a normal mash with a thickness of 1.4 quarts per pound.

Beer Stability, pH, and Dry Hopping

A topic that is likely to receive more attention in the near future is the relationship between beer pH and dry hopping. In general terms, dry hopping increases beer pH. Practical brewers and brewing scientists have noted that the very high dry hopping rates used for hazy IPAs have resulted in more packaged beers with pH > 5.0. Beer pH is usually in the 4.2–4.8 range and when beer pH gets into the 5s, oxidative and microbiological stability both take a dive. One technique that is really gaining some traction is wort pH adjustment after the boil to reduce pH going into fermentation to about pH 4.8. Brewers are also using post-fermentation acid additions to lower in-package beer pH to specifically address oxidative stability. Thanks for the great question about pH. Hope this information is useful in your quest for great beer!

Q John Palmer states in his book How to Brew “You should not aerate when the wort is hot, or even warm. Aeration of hot wort will cause the oxygen to chemically bind to various wort compounds. Over time, these compounds will break down, freeing atomic oxygen back into the beer where it can oxidize the alcohols and hop compounds producing off-flavors and aromas like wet cardboard or sherry-like flavors. The generally accepted temperature cutoff for preventing hot wort oxidation is 80 °F (27 °F).”

Since I’m using kveik yeast (Voss) that has an optimum pitch temperature of 102 °F/39 °C I’m a bit worried. Am I risking hot wort oxidation at that temperature?

Dirk Kissing
Almelo, Netherlands

A Several years ago, I was on a panel discussion at an annual MBAA (Master Brewers Association of the Americas) meeting held in Chicago. A question related to general suggestions about “stuff” was lobbed to the panel. Thanks moderator! Luckily, I waited to comment after the other panelists offered their sage advice about stuff. This gave me a little prep time to offer that brewers should avoid making absolute statements, especially when it comes to using process declarations as part of marketing. Seems like too many brewers make statements that are later backed away from as things change. This question kind of falls into that camp.

Many statements about process are often taken out of context. John Palmer’s point about not aerating hot wort falls under the “best practices” umbrella. No argument with that general rule. But general rules are just that; they are general and not intended to be absolutes. A great example of aerating hot wort is when traditional brewers use coolships and/or Baudelot coolers . . . those cool looking copper washboard things that sort of resemble an art deco urinal that could be found at a fancy beer hall. Coolships and Baudelot coolers (falling film chillers) expose hot wort to air, allowing the wort to pick-up oxygen from the environment upon cooling. That’s just part of the process with these devices, and commercial brewers who use them today for certain specialty beers do not have special rooms that are devoid of oxygen to prevent hot wort from being exposed to oxygen . . . although some brewer has probably done this or will be doing it after reading this jab!

Lines in the sand aside, you may want to consider if wort aeration is even required for what you are doing. There is a Voss Kveik dried yeast produced by Lallemand. Not sure of Lallemand’s general suggestions about wort aeration and dried yeast these days, but Lesaffre Yeast (producers of the Fermentis line of dried yeast) has been educating brewers about when aeration is needed. As it turns out, many, if not most, dried yeasts are propagated under conditions resulting in lots of glycogen. This is different from how yeast grow in a typical brewery fermentation, making the oxygen requirements of these yeasts different from yeast that have been harvested from a previous fermentation or grown under conditions that push yeast into anaerobic metabolism even when there is ample oxygen added to the propagator; the latter happens when the Crabtree Effect is in full-effect.

You could try aerating 79 °F/26 °C wort, pitching, and allowing the fermentation to warm up as action kicks in.

Let’s assume that you want to harvest and re-use your kveik yeast. Maybe you decide to use a traditional yeast stick or yeast ring, or maybe you use a glass flask equipped with a lid. Whatever the method, you plan to collect and re-use your yeast. Do you aerate your wort for subsequent worts? Brewing is all about pragmatism. Let’s assume you don’t aerate your wort and the yeast performs poorly. Your next move may be to aerate to see if aeration, or the lack thereof, affects fermentation. The way I see it, you don’t have to worry so much about beer oxidation if your yeast are not happy and healthy.

Now let’s go one step further. Assume that aeration does improve fermentation and beer flavor when re-using your yeast, but you discover that your beer is not so stable when stored. Now is the time to consider how aerating warm wort may be affecting stability. You could try aerating 79 °F/26 °C wort, pitching, and allowing the fermentation to warm up as action kicks in. The takeaway message is that general rules are never cast in stone and are intended as guidelines to help folks find success. Here’s to great beer and never saying never!

Q Here in Alaska, before the pandemic, two breweries served real ale from a beer engine. Now it’s just one, and it’s a few hundred miles away, so I’m attempting it myself, conditioning in a bag (bag-in-a-box style). So far, I’m not achieving what I hoped. I’m priming with wort, and put some in bottles, some in bags. The beer from the bottles is fine, but the hand-pumped beer from the bags lacks proper carbonation. The bags expand quite a bit, so maybe the additional headspace is the problem? Some have suggested I should vent the bags, but I worry the venting will also keep the beer from reaching optimal carbonation; we don’t vent bottle-conditioned beer, right? Please help.

Justin Herrmann
Homer, Alaska

A The bag-in-box method has never really been common among homebrewers, but is a technique used by many pubs around the world. The reason your beer is not carbonating is that a rigid vessel is required to house the bag. This allows the beer to be pressurized above atmospheric pressure and to become carbonated. The challenge with a bag-in-box type package for carbonated beverages is the seal required between the bag, the container, and the outlet to the environment.

The standard for this design uses stainless beer serving tanks to house specially designed liners equipped with an outlet spout that seals to the vessel with a special ring mechanism. These vessels are very common in Europe and are becoming more common in North America. Although it is possible to carbonate or condition beer in the bag, provided the tank pressure is high enough to prevent gas bubbles from forming, the standard method used with these tanks is to carbonate beer prior to filling. Since the liner separates beer in the bag from the atmosphere in the tank, high pressures can be used for beer dispense without affecting beer carbonation level. This same benefit also allows compressed air to be used for dispense without damaging the beer (shelf life varies by the type of liner). The liner also makes vessel cleaning much easier, and reduces water, cleaning chemical, and carbon dioxide consumption. Although the liners are recyclable, they are made from plastic and that is one of the few downsides to the general design.

Unfortunately for homebrewers, there are few small-scale choices of this type of container on the market. Mueller, Duo Tank, and Bier Drive are the primary suppliers of these vessels. Perhaps this idea could be explored as a new offering to the homebrewing market!

Your question is really more about producing cask-conditioned beer at home, versus how to serve beer from a bag. My suggestion is to use a soda keg to carbonate your beer if you are looking for the simplest approach. You can either rack your beer into your keg with some residual fermentables or rack into your keg after fermentation is complete and add priming wort or sugar. Whatever method you choose, a spunding valve (adjustable pressure relief valve) is a handy way to control the pressure in the keg. Although you can reliably dose sugar and carbonate without using a spunding valve, the method is not as easy. Conditioning method aside, you want relatively low carbonation if the plan is to serve something akin to cask ale.

I am a newer generation U.S. brewer, cutting my teeth in the late 1980s, and never really bought into the whole anti-bottled gas thing espoused by CAMRA (Campaign for Real Ales). If the idea is to serve beer with about 1.8 volumes (or whatever you want) of carbon dioxide using a beer engine, the easiest way to keep your beer fresh and the carbonation level consistent is to keep your keg pressurized. Beer at 50 °F/10 °C with an equilibrium carbon dioxide pressure of 9 psig contains 1.82 volumes of carbon dioxide. As long as you maintain this combination of temperature and pressure, your beer will be consistently carbonated at a pretty low level.

Although beer engines are simple to use, do interesting things to beer mouthfeel and foam, and look super cool, they are not designed for use with pressurized liquid because the design of the pump allows pressurized liquid to freely flow through the pump and out the nozzle. Two ways to prevent this from occurring is to either store the beer at a level that provides sufficient liquid head pressure to offset the keg pressure (in this example about 20 feet below the beer engine) or to simply install a check valve in the beer line. Check valves are normally designed to prevent back-flow, however, when used with a beer engine and a pressurized keg, check valves prevent flow out of the keg when the beer is not being actively pumped. Easy peasy!

If you do want to go old-school CAMRA, you can condition your keg, vent the keg to atmosphere, hook it up to your beer engine, and start pulling pints. The Achilles heel of cask ale is beer oxidation and the growth of aerobic beer spoilers, especially acetic acid bacteria. If you do decide to go
without external gas, you will want to consume your beer
in 3–5 days.

Issue: March-April 2021