I just finished brewing a Mild yesterday. It’s in the fermentor bubbling away at about 167F, but the gravity is a bit higher than I was planning. I ended up at 1.039-1.040 when I was aiming for 1.038. Initially I had 1.043 until I added a quarter gallon of water before pitching the yeast.
I thought back through my process and can attribute the higher gravity to two things: 1) I boiled off more water than I expected and 2) my efficiency was higher than the 70% I planned.
After the sparge, I ended up with 4.5 gallons of 1.036 wort, which is a total of 162GU. My expected GU was 152, and the max potential GU was 217.27, so I was closer to 162/217.27 = 75% efficient.
I might have been a few percentage points over 70 during most of my brews, but I close enough, and often I hit my targeted original gravity right on the dot. So I’m pretty sure that two things caused this: I mashed out with hotter water than normal and kept the grain bed at a slightly hotter temperature during the sparge. Rather than dump in water at around 175-180F, I boiled two quarts separately in a small pot and dumped it in at around 210F or so, close to boiling.
I sparged with water at 170-180F or so, which kept the grain bed above 160F. I’m not sure if I ever got close to 170F (the recommended mash out temperature), but I was definitely closer than in previous batches.
I also boiled off .75 gallons, slightly more than the .5 gallons I usually boiled off, which will be important to note in the future.
The key takeaway, though, is this: Raising the temperature of the grain bed with a significant mash out and maintaining that temperature during the sparge will increase your efficiency.
I think it might be time for me to start calculating recipes with 75% efficiency.