How does temperature and pH affect mashing and lautering?

Brewers manage the temperature and pH values to control enzyme performance in the mash, reduce tannin extraction during lautering, and to enhance yeast performance during fermentation, as well as the overall product quality (Buttrick, 2012). During mashing, the enzyme activity depends mostly on the temperature, it increases with rising temperatures and each enzyme reaches its own optimum range (Kunze, 2014). Raising the mash temperature increases the rate of catalyst reactions, accelerates the rates of protein unfolding and precipitation, quickens diffusion and dissolution steps, aids in mixing and at certain temperatures causes starch gelatinization and breaks down the cellular structure of endosperm tissues in unmodified (Briggs, 2004).  If the mashing temperature is below the optimum range for proper conversion, it may reduce grain extract and increase lautering duration (Agu, 2011). Different mashing temperature steps are designed to maximize the hydrolysis of different grist compositions. Proteases with an ideal range of 35-45°C break down the protein matrix holding the starch granules. Glucanases perform best at 45-55°C and break down hemicellulose gums, whereas amylases break down the starch granules and work best at 61-67°C (Buttrick, 2012). At higher temperatures enzyme inactivation occurs because of the unfolding of the three-dimensional structure of the enzyme called denaturation (Kunze, 2014). Wort fermentability can be altered by mashing temperature because of the lower denaturation temperature of β-amylase; attenuation will not be apparent until post-fermentation (Muller, 1991). The structure of the enzyme can also change depending on the pH value. The enzyme activity reaches an optimal value for both temperature and pH, which is specific for each enzyme and decreases at higher or lower temperature and pH values. The effect of pH on enzyme activity is in general not as large as the effect of temperature (Kunze, 2014).

Figure 1. The reaction of Bicarbonate in an Acidic Solution to Increase Alkalinity (Briggs, 2004)

The grist composition will be the largest influence of wort compounds produced with some considerations being malt to adjunct percentages, average protein content, and malt modification. However, brewhouse liquor has a significant effect on mashing and wort pH (Taylor, 1990). Interactions between calcium and magnesium ions and wort components have a critical effect on mash and wort pH by bicarbonate ions removing free hydrogen and raising the pH (Figure 1). Calcium and magnesium ions react with mash compounds such as inorganic phosphate, phytic acid, and less phosphorylated inositol phosphates, proteins, and peptides, contributing free hydrogen to the mash and lowering pH (Figure 2)(Briggs, 2004).

Figure 2. The reaction of Calcium Ions when Phosphoric Acid is used to Increase Acidity (Briggs, 2004)

Calcium phosphate is less soluble at higher temperatures causing mash pH to lower during decoction mashes and declines further during boiling. A source of error is from measuring the pH of wort or the mash is at ambient temperatures as weak acids separate more as the temperature increases so the pH of the solution falls. At 65°C, the pH of the wort is approximately 0.35pH lower than ambient temperature and 0.45pH lower at 78°C. As the temperature of mash changes from the different rests and mashing steps, so will the pH (Briggs, 2004).

Mashing a lightly kilned malt with distilled water results in a wort of about 5.8-6.0pH, this value is maintained by the natural buffering solutions from phosphates and proteins from the grist. Single-stage infusion mashes are run at a compromise range of 5.2-5.4pH which results in 5.5-5.8pH at ambient temperatures. Reducing the pH too many results in greater soluble nitrogenous materials but extends the saccharification time and reduces extract yield. Lowering the pH with calcium and other means accelerates the rate of degradation of starch, increases total soluble nitrogen and free amino nitrates and reduces wort colour. Simultaneously, alterations of the solubility characteristics of proteins occur, the buffering power of the wort increases, and eventual hop utilizations decreases (Briggs, 2004).  A result of the increase of the free amino acids released is that they contribute as aromatic pre-cursors while minimizing the formation of ferulic and coumaric acids (Schwarz, 2012). Further lowering the pH using lactic acid from either chemical or biological sources has been shown to improve the quality and processing of beers when the grist consists of 20% (Lowe, 2005) and 50% unmalted barley (Lowe, 2004).

Enzymes optimally within narrow pH ranges: peptidases are at 5-5.2pH; glucanases at 4.7-5pH; and β- and α-amylase are at 5.4-5.6pH and 5.6-5.8pH respectively (Buttrick, 2012).  In mashing, the hydrolysis of a substrate relies on the mixture in the grist, water to grain ratio, grind coarseness and grist distribution of particle. Similarly, the mash conditions and brewhouse operations can affect the optimum pH (Briggs, 2004). Unfortunately, the relationships between wort composition and the temperature are much better understood than that of wort composition and pH as there is limited research dedicated to the matter (Bamforth, 2001). However, the principal method of controlling the pH of the beer is during mashing; the extraction of buffering solutions of hydrolysing barley compounds will directly affect the final pH structure of the final beer (Taylor, 1990).

During wort collection, buffers are rinsed from the mash which increases pH, particularly if there are bicarbonate ions present in the sparge liquor. The higher pH draws unwanted polyphenols and flavours from the grain bed. Best practises are to maintain liquor pH are reducing bicarbonates and by using proper levels of calcium (Briggs, 2004). Additionally, maintaining the temperature of the grain bed during lautering is known to improve filtration by reducing the viscosity of the mash (Bühler, 1996)

During the hot break in the kettle, the wort pH reduces by 0.2-0.3 mostly from the further precipitation of calcium-based salts. This brings the wort near 5pH, which is ideal for vigorous fermentation for many yeast strains. Fermentation causes a drop of 0.5-07pH. At the end of fermentation, barley-based beers are approximately 4.1-4.5pH with wheat beers being slightly more acidic. Depending on the practices in the brewery cellar, beers such as lambics and other sour styles will have an even lower pH level from acid-producing bacteria (Buttrick, 2012).

References

Agu, R. (2011) Effect of Mashing Temperature on the Processability of Malted Barley. Tech. Q. Master Brew. Assoc. Am. 48(1), 4-8.

Bamforth, C. (2001) pH in Brewing: An Overview. Tech. Q. Master Brew. Assoc. Am. 38(1), 1-9.

Briggs, D., Boulton, C., Brookes, P., and Stevens, R. (2004) Brewing Science and Practice. Woodhead Publishing Limited, Cambridge, UK, 104-122.

Bühler, T., McKechnie, M., and Wakeman, R. (1996) Temperature Induced Particle Aggregation in Mashing and its Effect on Filtration Performance. Food and Bioproducts Processing, 74 (4), 207–211.

Buttrick, P. (2012) Mashing, in The Oxford Companion To Beer; Oliver, G. Ed.; Oxford University Press, New York, 576-578.

Kunze, W., Manger, H., and Pratt, J. (2014) Technology Brewing & Malting, 5th ed; Handel, O. Ed.; VLB, Berlin, 220-225.

Lowe, D. P., Ulmer, H. M., Barta, R. C., Goode, D. L., and Arendt, E. K. (2005) Biological Acidification of a Mash Containing 20% Barley Using Lactobacillus Amylovorus FST 1.1: Its Effects on Wort and Beer Quality. Journal of the American Society of Brewing Chemists. 63 (3), 96–106.

Lowe, D. P., Ulmer, H. M., Sinderen, D., and Arendt, E. K. (2004) Application of Biological Acidification to Improve the Quality and Processability of Wort Produced from 50% Raw Barley. Journal of the Institute of Brewing, 110 (2), 133–140.

Muller, R. (1991) The Effects of Mashing Temperature and Mash Thickness on Wort Carbohydrate Composition. J. Inst. Brew. 97, 85-92.

Schwarz, K., Boitz, L., and Methner, F. (2012) Release of Phenolic Acids and Amino Acids During Mashing Dependent on Temperature, pH, Time, and Raw Materials. J. Am. Soc. Brew. Chem. 70(4), 290-295.

Taylor, D. (1990) The Importance of pH Control During Brewing. Tech. Q. Master Brew. Assoc. Am. 27, 131-136.