Lesson 4 - The Mashing Process

If you haven’t already been told that pH and especially maintaining a lower pH is vital in brewing, you have now, and it will not be the last time you hear it! Mashing is arguably the point of the brewing process where we need to ensure pH is correct because it makes subsequent control easier.

The right pH enables our enzymes to work effectively

As we would expect from the enzyme-related theme to the unit so far, the main reason pH is important is to ensure our enzymes can operate as close to their optima as possible. The table below shows these optima.

Table: Optimum pH for mashing enzymes

Fortunately, the optimal pHs for most of the enzymes are in the same range, so we do not need to vary pH throughout the mash to ensure different enzymes can operate at their optima. One exception to this rule is that if we are using exogenous enzymes with an optimal pH outside this range. In this case, we could adjust the pH of the mash in the cereal cooker to the enzyme’s favoured pH before readjusting the main mash’s pH upon the addition of the cooked cereal. Modern enzyme products tend to work optimally at standard mash pHs so this is less common today. 

The pH we aim for is a compromise between achieving the optimum for our enzymes and achieving a pH that will provide the following benefits:

• Enhanced protein coagulation, producing more hot and cold break (trub) hence improving colloidal and microbial stability

• Improved foam stability

• Reduction in wort viscosity and hence improved wort separation

• Reduction in the extraction of polyphenols

• Lower colour forming potential (as long as pH is not raised before boiling)

• Increased flavour stability

A typical pH range for mashing is 5.2-5.4 at mash temperature.

pH changes with temperature

The pH of a solution falls as temperatures rise. As temperatures rise, the same molecular vibration that helps gelatinise starch causes weak acid molecules to dissociate, leading to the release of hydrogen ions (H­⁺). The table below shows the effect of temperature on the most common weak acid, water.

Table: Water pH at a range of temperatures

It would be nice to show a table for wort, but the effect is different for different solutions. There is no common correction factor. For wort, the pH at 65℃ is approximately pH 0.35 lower than at 25℃. From this, we can see that if we vary our mash temperature, we are also varying our mash pH! The pHs quoted in this lesson are measured at mash temperature (whatever that is at the time!).

Most other pHs you see quoted in brewing literature will be from measurements on samples cooled or warmed to either 25℃ or 20℃. It is important when referring to pH data to take account of the temperature at which it is measured.

Modern pH meters have automatic temperature compensation (ATC). It is important to understand that this does not account for the change in pH in the solution being measured, just the effects of temperature on the performance of the electrode.

Control of mash pH

Unsurprisingly mash pH is affected by the nature of the grist and the water. Solutions of all malts in distilled water are acidic. Most malt certificates of analysis will provide a wort pH based on a IoB, EBC/ASBC mash. As a general rule, the darker the malt, the lower the wort pH with pale malts at around 6 and highly coloured crystal or roasted malts at 5. So, for most beers (more than 90% of the beer consumed in the world is pale coloured lager), the pH of the mash would be too high if made with distilled or deionised water.

If you remember back to your lessons on water, you will already know the key ion for reducing (and to a certain extent controlling) mash pH. Calcium ions (and magnesium ions to a lesser degree) interact with substances dissolved in the mash, such as inorganic phosphate, phytic acid and other phosphorylated compounds displacing H⁺ ions into the mash and, hence reducing the pH. The equation below shows the precipitation of calcium phosphate, which is one of these interactions.

As well as achieving an overall reduction in pH, the effect of calcium ions also helps buffer (enables to resist changes) the mash and wort pH. This buffering effect is caused by an increase in the activity of phosphatase enzymes at the lower pH which increases the level of phosphate ions. The phosphate ions, buffer the wort which can lead to less of a drop in pH during fermentation. For this reason, some brewers add acid to the wort, reducing the pH to 5.1 – 5.2 before boiling. Many breweries add calcium chloride and sulphate to help maintain the correct pH. Figures of 50 – 100 mg/L of calcium are common. As well as the benefits provided by the reduction of pH, calcium also increases the stability of ɑ-amylase in the mash. So, calcium is our ionic hero, but there is also a villain lurking in brewing water in some areas. Bicarbonate ions increase pH by removing H⁺ ions, as shown in this equation.

Unless brewing with large proportions of coloured malts limiting the amount of bicarbonates in brewing water (or counteracting it by adding other calcium salts) helps achieve the correct mash pH. Calculations based on the concept of residual alkalinity (outlined in the Water unit) can be helpful for determining the pH of mashes for given water compositions, but most breweries will undertake trial mashes to find the correct rate of salt additions or ion subtractions heuristically.

Breweries that feel increased levels of sulphate and chloride are detrimental to beer palate do not have the option of using calcium salts. In this case, the best option is mash acidification using lactic, phosphoric, or mineral acid (not permitted in Reinheitsgebot), biological acidification or acid malt. Some breweries also use a combination of water treatment and then fine control with acids.

Biological acidification

In biological acidification, the brewery produces its own lactic acid in the form of sour wort (called Sauergut in Germany where the practice is most common). To produce sour wort, diluted first wort (the first wort to be run from the wort separation device) is added to a tank containing sour wort and a resident population of lactic acid bacteria. The lactic acid bacteria then ferment the carbohydrates in the wort under anaerobic conditions to produce lactic acid. The bacteria most commonly used are pure cultures of Lactobacillus amylovorus and Lactobacillus amylolyticus. They are unable to grow in the presence of hop acids, grow strongly in wort and do not produce diacetyl or toxins. The temperature of the acidification tank is maintained at around 46℃, and oxygen is excluded by sparging with CO₂. Acidified wort is added at mashing in, during first wort collection and before wort boiling. Biological acidification is claimed to provide a softer palate to beer along with the other benefits of controlling mash pH we covered earlier. It is also possible to buy commercially produced sour wort. Acid malts are produced by allowing lactic acid bacteria present on the malt to ferment sugars sprayed onto the grain or by spraying the grains with a solution of lactic acid from a biological source.

Hopefully, we have now provided enough evidence to prove that, as we said at the start of this section, pH control is vital to successful mashing. The next mashing parameter that we will investigate is mash thickness.