This is the fifth installment in the All-Grain Brew Day Walkthough, which started with a post on strike water preparation.
When the mash is over, there is a sudden flurry of activity by the brewer. The brewer should mash out by heating the mash directly, or infusing it with boiling water, to raise the temperature to 170 °F (77 °C). If a brewer has mashed in his or her kettle, he or she may heat the mash to a couple degrees above this, then scoop the contents over to their lauter tun (where it will hopefully settle in around 170 °F (77 °C). In addition, if the brewer expects — based on past experience — that the grain bed temperature will decrease during recirculation, he may heat the mash to a few degrees over 170 °F (77 °C). With the relatively low pH of an undiluted mash, excess tannin extraction is not a problem, even when the grain bed exceeds 170 °F (77 °C).
Many brewers new to all-grain brewing are surprised at the amount of boiling water it takes to raise the temperature from around 150 °F (66 °C) to around 170 °F (77 °C). As a rough rule of thumb, it takes a volume of boiling water equal to half the volume of the mash to make this change. In other words, if your mash occupied 6.0 gallons (23 L), you’d need at least 3.0 gallons (11 L) of boiling water for the mash out. If the brewer lacks space in his mash tun, such that a boiling water infusion is insufficient to raise the temperature to 170 °F (77 °C), add as much boiling water as possible. Even a small raise in the temperature of the grain bed can be beneficial. Plus, you can raise the temperature of the grain bed during wort collection by sparging with extra hot water. After mashing out, or transferring the mash to your lauter tun, let the mesh sit for about five minutes before proceeding to recirculation. Mashing out is not an absolute necessity, but the added heat (and stirring) help with lautering and your extract efficiency.
Recirculation is the act of drawing wort from the mash and returning it to the top of the grain bed. This filters and clarifies the wort. At the homebrew scale, a brewer will typically collect around 10–20 fl. oz. (300–600 mL) of wort per minute while recirculating — about the same rate as when collecting the wort, or slightly faster. Sometimes worts will clear quickly. Dark beer worts often clear very quickly. When making a lighter colored beer, clarification may take longer. If the wort does not appear to be clarifying with further recirculation, simply proceed to work collection. If you have recirculated for 20 minutes, or recirculated more than 25% of the wort, stop and proceed to wort collection.
On RIMS and HERMS brewing set-ups, recirculation and the mash out are combined into one step. In theory, a brewer with a picnic cooler mash tun could attempt something similar. By running off small amounts of wort, heating them to near boiling, and returning them to the top of the grain bed, he could recirculate and mash out at the same time. In practice, this may take a very long time.
For brewers who manually recirculate, this step is accompanied by a loss in temperature. This can be compensated for by mashing out to a few degrees higher than 170 °F (77 °C). The drop in temperature can also be minimized by stopping recirculation as soon as the wort is clear. In addition, the grain bed temperature can be re-raised by sparging with extra hot water during lautering.
Recirculation is another step that is not absolutely necessary. However, it will reduce the amount of break material produced during the boil and may help limit astringency because small pieces of husk material aren’t carried over to the kettle and boiled.
Once you are mashed out and recirculated, it’s time to collect the sweet wort from the mash. This process is called lautering. Lautering involves draining the wort entrained in the grain bed and rinsing the grain bed to further extract sugars and other carbohydrates. The wort that you would yield from draining your mash tun without adding any sparge water is called first wort. The volume and gravity of first wort depend on your mash thickness and how well your mash went. At a usual homebrew mash thickness around 1.25 qts./lb. (2.6 L/kg), and reasonable extract efficiency (around 70%), the specific gravity of the first wort can be around SG 1.090. It is common to rinse the grain bed after the first wort has been collected, and this process is called sparging. This recovers sugars from the grain bed, but yields less dense wort than the first wort.
In the next installment in this series, I’ll cover how to lauter, either by batch sparging or continuous sparging.