Lesson 8 - Mashing End of Unit SAQ

** Describe the effects of oxygen and calcium in mashing and how each can be controlled.

Response

Oxygen

Oxygen damages beer flavour stability and can lead to colour pick up in mashing. Oxygen reacts with fatty acids in the mash to cause precursors to compounds that give beer a stale flavour. These precursors are converted into stale flavour compounds in the package. The presence of oxygen in the mash and lipoxygenase (LOX) enzymes catalyses the oxidation of fatty acids. The most significant staling compound is E-2-nonenal which is formed from the oxidation of linoleic acid. Fatty acids also oxidise without LOX (autooxidation). It is therefore essential that we exclude oxygen from the mash. We can help exclude oxygen in the following ways:

• Fill vessels from the bottom under a cushion of deoxygenated water

• Purge oxygen from the mill, conveyors and vessels using CO₂ or nitrogen

• Mill the grist under deoxygenated water or aspirate the mill with CO₂

• Use deoxygenated mashing water

• Use an agitator design that avoids swirling and the formation of vortices

• Use mash transfer pipework that allows mash to flow evenly, keeping the pump flooded

• Flush transfer pipework with deoxygenated water before moving mash

• Use low agitator speed when mixing the mash

• Use low pump speed when transferring mash and ensure the pump is at the correct point on its design curve

• Design pipework to avoid sharp bends that cause shearing of the mash

• Prevent the pump from running dry at the end of mashing by chasing out mash with deoxygenated water

Calcium

Calcium is an essential ion in the mash. It is required as a cofactor by ɑ-amylase and also helps stabilise the enzyme at high temperatures. Calcium ions interact with substances dissolved in the mash, such as inorganic phosphate, phytic acid and other phosphorylated compounds displacing H⁺ ions into the mash and 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 helps buffer (enables it to resist changes) the mash and wort pH. This buffering effect is in part caused by an increase in the activity of phosphatase enzymes which operate more effectively at a lower pH. Phosphatase enzymes release further phosphate into the wort, increasing buffering capacity. Levels of 50 – 100 mg/L of calcium in mashing water are commonly suggested as optimum for the control of mash pH. Above a certain concentration, calcium and the anions associated with it are likely to affect the palate of the beer, so it is important we do not overdo it.

To control calcium ion concentration, we need to measure the amount of calcium in the mashing water and then add or remove calcium to achieve the target concentration. We can remove calcium with reverse osmosis or ion exchange. If the ionic composition of the water is otherwise acceptable, we can treat a proportion of the water with reverse osmosis or ion exchange before blending the treated part with untreated water to achieve the correct calcium concentration. If there is not adequate calcium in the mashing water, we can add calcium chloride and calcium sulphate in order to raise the level.