Mash temperature: 148 versus 156 on the same grain bill
I had read many times that mash temperature controls how much body a beer has, and I believed it in the way you believe things you have never tested. In March I brewed the same recipe twice, one week apart, changing nothing except the temperature of the mash. The grain bill was 5 pounds of pale malt and 8 ounces of a medium crystal, mashed in a small insulated cooler with 1.5 quarts of water per pound, which for this bill is a little over 8 quarts. Same hops, same yeast from the same packet split in two, same water from the same tap.
Before either batch I checked my thermometer in a glass of crushed ice and water. It read 33 °F, so I subtracted a degree from everything that followed. It is a two-minute check and I had never done it before; I now do it every brew day.
The first mash I aimed at 148 °F. I preheated the cooler with a quart of hot water for ten minutes, poured that out, and added strike water at 160 °F, which after stirring in the grain settled at 149. Over the 75 minute rest it dropped to 147. The wort tasted thin and sweet, as expected. Preboil gravity was 1.038 in 3.4 gallons, and after the boil I had 2.5 gallons at 1.049. It fermented out to 1.008. The second mash I aimed at 156 °F, with strike water at 168. It landed at 156 and finished the 60 minute rest at 154. Preboil gravity was 1.039, the finished wort 1.050, almost identical to the first batch. It fermented to 1.015.
The difference in the glass is bigger than seven gravity points sounds. The 148 beer is dry, crisp, and a little hollow in the middle, with the hops standing out sharply. The 156 beer is rounder and fuller, slightly sweeter, with the crystal malt more obvious and the hops softer. Both are drinkable. Neither is what I would call balanced; the truth for this recipe is probably somewhere around 152, which is where I had been mashing all along by habit.
What I take from it: the starch conversion at the cooler end takes longer, so the extra fifteen minutes of rest was worth it; a two degree drop over an hour in a small cooler is normal and I should aim a degree high; and the cheapest experiment in brewing is to change one thing and brew twice.