I ran across this thread a couple of weeks ago and was instantly intrigued by the prospect of a low-ABV/high-flavor brew. I love my Belgian quads, but they are not the ideal beverage for losing the weight I gained over the past 18 months. Yesterday was my first attempt at low-T mashing. Here's my report:
I do mash-in-a-bag (MIAB) in a 10 gallon cooler. My target was a 2.5 gallon batch with OG=1.020. As suggested here and elsewhere, I plugged in 25% efficiency to the Brewer's Friend calculator to develop the following grain bill:
4.5# Maris-Otter
0.5# Aromatic
0.25# Crystal 75
I chilled the strike water to 58 degrees F. After dough-in, the temp was 63 F. Over 3.5 hours, I stirred occasionally and then lifted the bag. Left behind was a very cloudy, starchy suspension. After draining off the wort, a fair bit of starch sludge was left behind in the cooler. A small amount of additional starch came out of suspension in the pot. I followed with two batch sparges. For each running, I attempted a gravity measurement with a refractometer. In all cases, it was hard to get an accurate reading because the field was blurry. But for the record, here they are:
Running | Volume (gallons) | Approximate Gravity |
1 | 1.85 | 1.017 |
2 | 1.3 | 1.007 |
3 | 1.05 | 1.004 |
I heated the 4.2 gallons to 152 F and turned off the electric burner. Over the next 25 minutes, the temperature rose to 154 then dropped to 148, at which point I turned the heat back on. I took another gravity measurement, and it was 1.021. Oops! Too high! This equates to 1.035 at 2.5 gallons (though I have found that these simple calculations are typically overestimates). Clearly there was more starch in suspension that got converted than I had hoped.
To keep the gravity reasonably low, I decided to boil down to ~3 gallons rather than 2.5. In the end, after boiling, chilling, and filtering, I ended up with 3.1 gallons of wort with OG=1.026 as measured by a hydrometer. I pitched a pack of WLP002 yeast and it's now bubbling away.
The Brewer's Friend calculator indicates that my actual efficiency was 41% -- much higher than expected. The issue I think is that I didn't make much of an attempt to limit the amount of starch in suspension or let it settle, especially after sparging. Next time, I will try giving at least 30 minutes for the starch to settle after lifting the bag. For now, it looks like I will end up with a 2-3% beer rather than my target of 1-2%.