Hey, thanks for all the replies! Apparently, I've got some changes to make in my procedure.
First, answer some questions.
How much wort did you leave behind in your mash tun?
Hardly any? Whatever was left on the bottom of the manifold, or soaked into the grain.
What was your intended starting gravity and final gravity?
The recipe says we were aiming for SG=1.050 and FG=1.013, which I didn't adjust at all, but probably should have.
How much did you boil off?
I'm not 100% sure on this, we boiled with covers on the pots, but I'm sure we still lost a fair amount, probably a couple litres. Is there any good way to measure this? Does anyone have some sort of volume markings in or on their boil pots?
How many lbs of grain did you use?
4.5kg, so about 10lbs?
What was your mash temp at mash in and what was your temp before sparging?
At mash in, we started with about 13L = 14qts of water at 77C = 170F, after the thermometer had a minute to adjust we got a reading of 68C = 154.4F, and by the end of the mash, we were at 66C = 150.8F.
Based on my experience a low gravity usually means you used too much water, thus diluting your wort too much.
Well, 9.9lbs of grain with 13.7qts of water is about 1.4 quarts/lb. That's less stiff than I thought, actually. But, we only sparged with an equal amount of water, so I'm not sure that would be the issue.
Did you take a pre-boil reading?
No, I did not. This is probably one place where I went wrong. The SG readings that we took were after the boil and the cooling, immediately before pitching the yeast.
Firstly what efficiency would you expect going on your other brew? Does it fit with the suggested efficiency from the recipe or should you have adjusted to hit the target gravity?
I can't find my brew notes on my last beer, I've moved twice since then, and they've just gotten lost in a sea of crap, which sucks. But I'm pretty sure that my efficiency on that one was somewhere around the 60% mark. But based on the last question there, I may have gotten the measurements at the wrong times, so that could be skewed as well. And yeah, 60% isn't what the recipe was made for, and I didn't adjust for that, my bad. This brew was a bit of a last minute thing, so I just picked a recipe for a beer that I knew I liked and hoped for the best.
Also I'm assuming your pitching temperature was somewhere around the 20 deg C mark but if it was hotter that may give you an extra point or so.
We probably pitched a little higher than that, actually. We only chilled the wort to about 40C, as I don't have a chiller. I've got about 2 feet of snow on my back deck, so the pots just went out in the snowbank for a while until they chilled a bit. But then they sat in the carboys inside while we cleaned up, so I'm sure we probably pitched around 30C or so. And yeah, I probably should have adjusted the reading for that. I kind of forgot to do that too.
For this brew you can accept a slightly lower ABV or you could bump it up with a touch of extract.
Yeah, this brew should be fine if it runs a little low. The LHBS didn't have Northern Brewer, and I didn't know offhand what a good substitute was, and they recommended more Kent Goldings, so the bittering hops we used didn't have a very high AA%, so in the end it may turn out to be more of a mild than a bitter, which is fine.
From most of the comments that are here, I'm thinking that a big part of my problem is sparging too cool. I don't have any kind of propane burner or anything, so I'm using two 20qt stock pots to boil. In this particular brew, I lautered into those two pots, so I had to heat up the sparge water in dutch ovens and regular cooking pots, so I couldn't get a lot done at once. We ended up not heating the water for very long because we needed to heat more than one batch, and we figured it would be better to go a little lower, but have all the water added close to the same time, than to try to go higher, but in a couple of smaller doses spaced further apart.
I think next time I'll run the sparge into a spare brewing bucket and heat up the sparge water in the brew pots, and then once the wort is collected, pour from the bucket into the pots. And definitely bump up the temperatures a little bit.
When should I be taking readings? I've been doing some reading on the site here, and it seems like I should be checking gravity of first runnings, final runnings, and pre-boil? (From an efficiency point of view, at least.) Do most people check gravity that often during a brew day? I've only been checking right before I pitch the yeast so far.
We're going to try to be brewing either 10 gallons once a month, or 5 gallons every 2 weeks, so we should have plenty of opportunity to fix the methods a little bit.
Thanks for all the help so far, all!