I’ve got a similar situation to singindave’s missed target gravity, but for the most part I’m hoping for some ideas as to what could have gone wrong (my yeast is already working happily, so I’m a little late to fix it now).
The other night I was brewing a stout with a target OG of 1.069, and wound up with an actual reading of 1.062. Going into the brewkettle I had a SG of 1.056 (after temperature correction), 1 point under my target of 1.057. My usual target volume before boiling is 7 gallons, but for this batch it was probably closer to 7.25 gallons.
Was it the extra volume that threw off my brew, or can you think of anything else that could affect it?
Did you end up with a greater volume than you expected? It’s not like the sugar boiled off, so if you went from 1 point off to 7 points off then I suspect your boil wasn’t as vigorous as usual and you ended up with a greater volume than normal. Or one or both of your measurements is wrong.
Were you brewing a stronger than usual batch- IE batch-sparging with a lower than usual pound/qt ratio? This could be a loss of efficiency. Often times it helps to add extra grain to compensate for stiffer mashes.
Sure… it’s great to take preboil measurements but beware of the beer faeries or gremlins. You’ll go mad… The only measurements I make are pre-pitch and post-ferment.
I’m the same way. Unless you have a reasonably accurate way to measure your pre-boil volume, and unless you stir really well to make sure the wort is completely mixed, any calculation you make to determine gravity points from the mash is going to be off.
If it bothers you, you can add a lb of sugar to the fermenter. Just make sure it is fresh store bought and sealed or use a lb of honey heated up in a pyrex measuring cup and take it to ~140-150, cover it and let it cool then add it to the fermenter. Yeasties will know what to do. Of course it may thin the body of the finished stout a bit. Your call.
I take multiple gravity readings with a refractometer all throughout my process and then use total Gravity Units (GUs) to see where I am at on the fly. Typical readings I take along with volumes are:
First & Second Runnings from Batch Sparge
Preboil
30 min Boil
45 min Boil
60 Min Boil
Post-Boil
It only takes me a minute or two and it’s helped me refine my boil-off. What I really like is determining my target Gravity Units for the batch (SG X V, e.g. 1.066@12 gal = 66 X 12 = 792 GUs). I use that to determine how close I am to pre-boil fermentables. One time on a low gravity partial mash batch, I had my total gravity units after my first run-off, so I just topped with water and boiled and did not need the DME. Lately I’ve been trying to record my first batch sparge numbers to figure out my efficiency for a no-sparge batch.