After fermentation, there is usually still wort left in the grain bed. In order to completely drain the wort, we have to spray hot water into the grain bed through a ring with a nozzle, which is called water spraying. In general, the refilling is divided into three steps and lasts about 90-120 minutes. In the first step a smaller amount of hot water, about 20%, is needed for the extraction of the first wort. In the second step, more water (about 50%) flows through the grain bed, so the remaining wort is much less. Afterwards, we use 30% of the hot water to further clean the grain bed in order to increase the wort yield.
How much hot water will be used in total in this process? This is related to the amount and consistency of the first wort and the concentration of wort in the full brew kettle. If brewing a pale ale/lager, the wort concentration is very low and therefore the amount of hot water required is correspondingly low. On the contrary, if brewing a dark beer, a large amount of hot water is required for refilling due to the high wort concentration.
In addition, we must pay more attention to the temperature of the filling water. The higher the temperature of the refilling water, the faster the refilling will be and the more wort will be discharged. However, it should be controlled within a reasonable range, 76-78℃, and not more than 80℃. Otherwise, too high temperature will make the α-amylase inactive, then the starch can’t be broken down. This means we can’t fully utilize the material.