Lesson 4 - The Mashing Process

Mash thickness is set by the ratio of water to grist (L of water:kg of malt) and is also known as the water to grist ratio. Ratios used vary depending on the method of mashing and wort separation employed and also the nature of the wort required.

Water to grist ratios from 2:1(thick mash) to 5.4:1(thin mash) can be used, and the ratios in the table below are ranges for each of the common wort separation devices.

Table: Water to grist ratios for the common wort separation devices

Thicker mashes are harder to pump and agitate and produce more viscous worts.

In thicker mashes, there is a high concentration of enzymes and substrates, and there is less water around. The high concentration of sugars and dextrins can slow amylase activity by competitive inhibition. Competitive inhibition of enzymes is when molecules block the active site on the enzyme preventing it from binding with its substrates and preventing it from catalysing the reaction. This means that starch conversion is slower in a thicker mash. Very thick mashes have low extract efficiency, but within the range displayed in the table above, there is only a minor difference between the thickest and thinnest mashes.

At high mashing temperatures, thicker mashes produce wort with a higher proportion of fermentable sugars. However, at standard mashing temperatures, thinner mashes produce a more fermentable wort. At lower temperatures, thin mashes favour proteolysis, while at higher temperatures, they favour starch breakdown.

Thick mashes produce higher levels of total soluble nitrogen (TSN), and FAN and more high molecular weight nitrogenous substances remain in solution. However, there is a lower proportion of foam enhancing polypeptides and proteins leading to poorer foam stability in the finished beer. This is due to the increased stability of the proteolytic enzymes in a thicker mash. The increased stability results from the solid material in the mash protecting the enzymes from temperature fluctuations, almost like insulation.

As there is a higher concentration of grist, the pH of a thicker mash tends to be lower and resists changes in pH more readily. By way of a summary, let’s compare and contrast thick and thin mashes in a table.

Table: Thick versus thin mashes