A major difficulty follows from the habit of measuring the pH of worts or mashes at
room temperature and assuming that these values apply at higher temperatures, when they
do not (Hopkins and Krause, 1947). Weak acids, like water (see Appendix), dissociate
more as the temperature rises and so the pH values of their solutions fall, like the pH
values of mashes (Table 4.
. Thus at 65 C (149 F) the pH of a wort is likely to be about
0.35 pH unit lower than at room temperature and 0.45 lower at 78 C (172.4 F). As the
temperature of a mash changes (decoctions, temperature programming, sparging) so will
the pH. These differences are significant, yet in many reports it is unclear if pH values
have been determined at wort- or mash-temperatures or on cooled samples. Probably the
latter is most usual. The pH optimum of -amylase, determined at room temperature, is
about pH 5.3, but its optimum estimated from mashing experiments is often reported to be
about 5.7. This error is due to the pH having been determined on the mash after it was
cooled, when the pH had risen. Because of this difficulty the pH optima of changes
occurring in mashes are a little uncertain (Table 4.9).
Mashing pale malt in distilled water usually gives a wort with a pH of about 5.8ÿ6.0,
this value being maintained by the buffer substances (including phosphates and proteins)
Table 4.9 `Optimal' pH values for `normal' isothermal infusion mashes made with pale malts
lasting 1±2 h. at 65.5 ëC (150 ëF). Data from various sources. As far as possible the temperatures
(mash temperature,m , and cooled wort, w), at which the pH values were determined are indicated
(see text for a warning)
Characteristic `Optimal' pH
Shortest saccharification (dextrinization) time 5.3 m±5.7 w
Greatest extract obtained 5.2±5.4 m?
Greatest extract from a decoction mash 5.3 m±5.6 m?
The most fermentable wort 5.1±5.3 m?; 5.4±5.6 w?
Mash impossible to filter <4.7
-Amylase most active (+ Ca2+) 5.3 m±5.7w
-Amylase most active 5.1±5.3 (4.7?)
Maximum yield of PSN 4.4±4.6 m; 4.9±5.1w
Maximum yield of formol-N 4.4±4.6 m, 4.9±5.2w
Maximum protease activity (depends on substrate) 4.3 m; 4.6±5.0 m?
Maximum phytase activity about 5.2m
Carboxypeptidase activity maximal 4.8±5.7
Αυτά γράφει ο Briggs στο βιβλίο του και συμφωνεί με τα γραφόμενα του Braukaiser
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