Low ABV

Mashing
1

IPA recipe from NB (Sierra Madre).
I mashed at 150. Could have been slightly cooler (147) for one hour.
Gravity of 1.034
fermented for 2 weeks. Yeast starter 12 hours ahead of pitching.
Final gravity 1.015

What could account for a low ABV?

Thank you.
Tim

2

Most likely causes, in order:

  1. A poor crush. Crush till you’re scared next time and that will most likely fix the problem.
  2. High volume. Did you get more than 5 gallons? This will obviously dilute the gravity.
  3. Thermometer reads low by like 10 degrees. This would kill some of your enzymes and cause poor conversion and attenuation.

My guess is #1. Fix that and you’ll probably not need to worry much about the other 2.