The Methods of Mashing
A popular multi-rest mash schedule is the 40°C - 60°C - 70°C (104 - 140 - 158°F) mash, using a half hour rest at each temperature, first advocated for homebrewers by George Fix. This mash schedule produces high yields and good fermentability. The time at 40°C improves the liquefaction of the mash and promotes enzyme activity. As can be seen in Figure 79 - Enzyme Ranges, several enzymes are at work, liquefying the mash and breaking down the starchy endosperm so the starches can dissolve. As mentioned in the previous chapter in the section on the Acid Rest, resting the mash at this temperature has been show to improve the yield, regardless of the malts used. Varying the times spent at the 60 and 70°C rests allows you to adjust the fermentable sugar profiles. For example, a 20 minute rest at 60°C, combined with a 40 minute rest at 70°C produces a sweet, heavy, dextrinous beer; while switching the times at those temperatures would produce a drier, lighter bodied, more alcoholic beer from the same grain bill.
If you use less well-modified malts, such as German Pils malt, a multi-rest mash will produce maltier tasting beers although they need a protein rest to fully realize their potential. In this case the mash schedule suggested by Fix is 50 - 60 - 70°C, again with half hour rests. The rest at 50°C takes the place of the liquefaction rest at 40°C and provides the necessary protein rest. This schedule is well suited for producing continental lager beers. These schedules are provided as guidelines. You, as the brewer, have complete control over what you can choose to do. Play with the times and temperatures and have fun.
Multi-rest mashes require you to add heat to the mash to achieve the various temperature rests. You can add the heat in a couple of ways, either by infusions or by direct heat. If you are using a kettle as a mash tun, you can heat it directly using the stove or a stand-alone hotplate. (See Fig. 84) The first temperature rest is achieved by infusion as in the Single Temperature mash described above. The subsequent rest(s) are achieved by carefully adding heat from the stove and constant stirring to keep the mash from developing hotspots and scorching. The mash can be placed in a pre-warmed oven (125 - 150 °F) to keep the mash from losing heat during the rests. After the conversion, the mash is carefully poured or ladled from the mash tun into the lauter tun and lautered. The hot mash and wort is susceptible to oxidation due to hot side aeration (HSA) due to splashing at this stage, which can lead to long term flavor stability problems.
Figure 84 - Mashing on the Stove- The grist is added to a pot of hot water on the stove for the first temperature rest. The mash is then placed in the oven (warm) to help maintain the temperature for the desired time. Then the mash pot is returned to the stovetop to be heated to the next rest. After mashing the mash is transferred to the lauter tun and lautered into the boiling pot. The mash tun is then used to heat water for the sparge.
If you are using a picnic cooler for your mash tun, multi-rest mashes are a bit trickier. You need to start out with a stiff mash (e.g. .75-1 quarts per pound of grain), to leave yourself enough room in the tun for the additional water. Usually only 2 temperature rests are possible with this method because the amount of heat necessary to change the temperature of the mash increases with each addition. Reaching a third rest is possible if the change in temperature is only a few degrees. For example, raising the mash temperature for 8 lbs. of grain from 150°F to 158°F at a mash ratio of 2 quarts per pound would require approximately 2.7 quarts of boiling water.