Mash pH and Why It Matters for All Grain Beer Brewing

by Brad Smith on May 7, 2015 · 11 comments

MashTempMash pH is an important concept for all grain brewing. While you can make “good” beer without worrying about pH, brewing truly great all grain beer relies on understanding the concept of mash pH and its impact on beer.

Understanding pH

You probably had a simple introduction to the concept of pH in your High School Chemistry course. pH is simply a measure of how acidic or alkaline a solution is. It is measured on a scale from 1-14 with 7 being a neutral reading. Pure water would have a reading of 7. Readings below 7 are said to be “acidic”, and readings above 7 are said to be “alkaline” or “basic”. The scale is logarithmic (technically pH is the log of the hydrogen ion concentration or pH = -log[H+]), so a pH of 5 is 100 times more acidic than a pH of 7.

pH is typically measured using either paper test strips or with an electronic device called a pH meter. Some brewers also use chemical test kits (like you might if you own a pool) to measure pH.

Why Mash pH Matters

We can talk about the pH of your brewing water, the mash mixture, the pH of your wort and even the pH of the finished beer. Each of these has a slightly different impact on the beer, but the most important for the all grain brewer is the pH of the mash mixture while its in the mash tun. In particular we want to keep the measured pH of our mash in the 5.2-5.5 range with a preference towards the lower end (5.2).

A lower mash pH (near 5.2) has the following benefits:

  • Improved enzyme activity during the mash, leading to better conversion of starches to sugars
  • Lower pH in the finished wort which improves yeast health during fermentation, and also inhibits bacteria growth
  • Improved hop extraction rates in the boil
  • Better protein and polyphenol precipitation both during the cold break and post fermentation
  • Improved clarity in the finished beer with reduced chill haze
  • Improved flavor and clarity stability as the beer ages

Factors Affecting Mash pH

Mash pH is very difficult to predict in advance. Though some large scale commercial brewers are able to accurately predict mash pH for certain recipes, they are often brewing the same recipe with exactly the same malts under exactly the same conditions repeatedly. Unfortunately variations in malts and water make this impractical at the home level, where often we brew with different recipes and ingredients every single time.

Some sources of the factors that affect pH include:

  • Water Used: The chemical composition of the water is a large driver in mash pH. Calcium, magnesium, carbonates and bicarbonates are all drivers of mash pH. While I can’t cover a complete course in brewing water or residual water alkalinity here, its important that you have good brewing water to brew with. Most water sources are slightly alkaline, so they tend to drive the mash pH above the desired 5.2-5.4 range.
  • Malts: Malts tend to be acidic, which means that they lower the mash pH of the overall mixture. Dark malts in particular can be very acidic, which is why many darker beers require little mash pH adjustment. Lighter malts have less buffering capability, so lighter beers often need additives covered blow to drive the mash pH down to the desired level. Unfortunately the acidity of malts varies widely and is not measured and published, so prediction of mash pH in advance is very difficult.

Measuring and Adjusting Mash pH

Because it is almost impossible to predict your mash pH in advance for a given recipe, you must measure and then adjust the mash pH for each batch you brew. You can measure the pH using precision test strips (get ones specifically designed for brewing), a pH meter or a chemical test kit. Be sure that your measuring method has the sensitivity to measure small changes in the 5.2-5.4 range – some test strips and kits are not designed to measure these small ranges.

In most cases your measured mash pH will be too high, which means you will need to add an acid or buffering agent to the beer to adjust it down. Some options include:

  • Lactic Acid – An organic acid produced by bacteria. Many home brew stores sell it in liquid form that is about 88% by weight solution, though this does vary so please refer to the instructions on the package. It is added a little at a time until you reach your target pH. It generally mixes well with beer flavors in the small quantities needed to adjust a typical mash.
  • Acid Malt – This is typically pilsner malt that has been acidified using lactic acid and contains about 3% acid by weight. Acid malt is primarily used in Germany to comply with strict purity laws (Reinheitsgebot) that prohibit additions other than malt, water, yeast and hops to beer.
  • Phosphoric Acid – An inorganic acid widely used in soft drinks. It replaces bicarbonate with phosphate and increases the phosphate content of the wort.
  • Hydrochloric and Sulfuric Acid – Used by many commercial brewers, these acids are usually not widely available to the public. These can be dangerous to handle (are both highly caustic) and are not recommended for use by home brewers, and also can create significant off flavors if misused. Also do not use the muriatic acid found in pool supply stores as it is not food grade and should be avoided.
  • Buffers such as “5.2 Stabilizer” – These salts lower the mash pH by reacting with phosphates brought in by the malt. They can raise the hardness of the mash water in the process, but they are a great “fire and forget” alternative since you can often add a pre-measured amount of buffer to the mash and achieve the desired range.

This was a brief overview of why its important to manage your mash pH – if you have your own tip please leave it below! Thanks for joining me on the BeerSmith Home Brewing Blog. Be sure to sign up for my newsletter or my podcast (also on itunes…and youtube…and streaming radio station) for more great tips on homebrewing. Also check out the How to Brew Video series I shot with John Palmer if you want to learn more about all grain brewing.

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{ 7 comments… read them below or add one }

Hugo Patino May 8, 2015 at 2:45 pm

Thank you for the article. Is no big deal, but just to clarify one point. The yield of isoalpha acids decreases as the pH of the wort is lower. In other words, a higher yield (of isoalpha acids) results at higher wort pH levels. For a good picture of this, please take a look at Figure 3 of the paper that can be found on the following link:
Regards, Hugo

DaveS May 10, 2015 at 4:42 pm

When exactly do you adjust the mash pH? Is if after the mashing is complete but before the boil or is it done earlier than that?

James Magesty June 22, 2015 at 1:19 pm

Very informative.However,I have the same question as DaveS point it.

Best Regards,


Ryan Kring November 16, 2015 at 2:34 pm

Typically you would measure 5 minutes into your mash to get your original PH then adjust. Give 5 and re-test. I have found that to be effective. You can even check you water ahead of time as well, especially if you are on a well.

Steve May 27, 2016 at 3:34 am

If you are adding Calcium carbonate you need to add it to the mash directly as it is not very soluble. If you add it to mash water, you end up with a white sludge in the bottom of your hlt.

Shane June 13, 2016 at 1:09 pm

Where is gypsum? Calcium Sulfate? When do you add it and why? Seems like one of the easiest ways to lower pH.

A. J. deLange July 25, 2017 at 3:33 pm

It is quite possible to predict mash pH fairly accurately in many cases depending on how closely the models for the malts used in the program match the actual properties of the malts the brewer is using. Some programs are better than others at this. As there are variations in the ‘same’ malt between lot numbers, growing seasons, cultivars, moisture content… it is not possible to get spot on predictions unless the brewer measures the properties of the individual malts himself and it is far easier to just check the pH of a test mash.

Buffers, such as 5.2 stabilizer do not work because, while it is true that phosphate buffers are effective this is only, as is the case with any buffer, near one of the pKs of the acid (phosphoric acid). Mash pH is about as far away from the pKs of phosphoric acid as one can get.

This product does not increase the hardness of mash or water treated with it because the phosphate salts in it are sodium salts and sodium does not contribute hardness.

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