Lesson 4 - The Mashing Process

With our focus on gelatinisation and enzymes, it’s easy to miss the other effects of temperature. Let’s find out more.

An increase in temperature increases the energy and movement in the mash. At a molecular level, this can break down some material, especially if the temperature is high. Increasing temperature also increases the rate at which substances are dissolved into water. This means at high temperatures, significant amounts of compounds that we do not want in wort can dissolve. Polyphenols, pentosans and β-glucans can be extracted in problematic amounts at the higher temperatures associated with decoction mashing where portions of the mash are boiled. Boiling mash also leads to colour and flavour formation, which is welcome in dark beers but must be avoided at all costs in pale ones.

With lipids, there is an interesting relationship with mash temperature. Higher temperatures favour their dissolution (or at least that of their breakdown products,) but higher temperature also denatures the enzyme(s) (LOX) that oxidises them to precursors of stale beer flavour. That said, minimising the amount of heat the wort is subject to has been identified as key to keeping beer tasting fresher for longer. Using a high mashing in temperature just to denature LOX is not a practical option but avoiding low mashing in temperatures in most cases is.

Last but not least, wort viscosity falls as temperature rises which is one of the reasons for the higher temperature selected for mashing off. Less viscous mashes are easier to pump.

Brewing, and by implication mashing, has been described as a process of compromise. Nowhere is this so true as with mashing temperature. We need to minimise temperature to save energy and minimise damage to enzymes and dissolution of polyphenols but maximise its effects on starch dissolution and gelatinisation. We will learn the clever ways we can strike this compromise when we discuss mashing methods later in the lesson.

Control of temperature

We have two main means of affecting mash temperature. Our first is the temperature of the water used to mash in. The temperature of this water is called the strike temperature. This is adjusted to the temperature required to achieve the target starting temperature for the mash. The grist added should always be at a lower temperature than the water, so the strike temperature needs to take account of the probable reduction in temperature caused by the grist. Interestingly the hydration of the grist actually produces heat. This is called the slaking heat or heat of hydration. We can estimate the start temperature of the mash from the amounts and temperatures of water and grist using this equation:

Where:

This is only a rough estimate because it does not factor in any ambient heat losses or losses or gains from the mashing vessel. For very thick mashes (1.5 parts of water to 1 part of grist), it is not possible to achieve high starting mash temperatures if the grist is cold.

Once in the mashing vessel, we can increase the temperature by heating via external jackets filled with steam or by adding steam or (very rarely) hot water to the mash. Control of temperature is typically automatic with temperature probes in the mash connected to a temperature controller that applies the heat to the vessel. Owing to the heterogeneous nature of mash, it is very difficult to obtain an accurate temperature measurement. A common problem is clumps of hydrated grist sticking to the sensing probe, hence insulating it from the bulk mash temperature. We will cover mash temperature control in more detail in the Mashing Technology lesson.

Temperature and time

It is important to appreciate that mashing and its component processes take place over a specific period. The time that the mash is subject to particular temperatures affects the extent to which the processes of dissolution and hydrolysis proceed. The time at which an enzyme is subject to a temperature at the upper limit of its operating range also affects the denaturation of that enzyme in the mash. The most important time in mashing is, of course, the amount of time allocated to it in the brewhouse cycle. We need to complete the objectives of mashing in the minimum possible time.

We can now move on to discuss another important factor in mashing, pH.