Low OG, how and when to raise

Yesterday I began work on only my second brew - a DFH 90 min all grain. The recipe called for an estimated OG of 1.075-1.090. I struggled a little with the mash temperature and it took me about ½ hour to get the temperature right. Once I did I let it sit for about 40 min after reaching that temp (probably not long enough?). I sparged and got my boil kettle to 6.5 gallons (that’s all it would hold) and everything else went good, but I boiled off a lot of wort over a 105 min boil and I ended up with just over four gallons 4 gallons. I will note that it took a long time to achieve a boil.

Before transferring to the fermenter I took a hydrometer reading and got 1.06. I then transferred to the primary, added almost 1 gallon of water to get to 5 gallons and pitched the yeast. Shook it all up nicely and took another hydromerter reading and this one came in woefully low at 1.04. This morning I looked at the fermenter and it looked like the contents were boiling there was so much activity. The airlock didn’t pop off, but krausen did escape and splattered the wall. That seems to have receded a bit so no big time blow off hose is necessary at this point.

That all said, it looks like I messed up and did not get good extraction. I want to raise the gravity and was wondering how I would do it and at what point in the process I should do it. As always, thanks in advance for all the help.

I got a frustratingly low OG reading last batch, but realized that I simply hadn't mixed the added water and the wort well enough. Maybe this is the cause? If you mixed it well, then I have no idea :x

It's too late now, but I would have boiled up some DME in that 1 gallon you topped up with. That would have keep you from diluting the wort. So, keep that in mind for next time- I always have some DME on hand for starters and just in case I miss my OG.

In this case, you could boil up some DME in some water, cool it and add. If you have brewing software, it could help you figure the exact amount, but 2 pounds DME in a little water should add about 16 points to your OG.

4 gallons for 1.060 = 240 points... dilute that to 5 gallons and you get 240/5 = 1.048.

You could have sparged about a gallon more and held it in a bucket until your main wort evaporated enough to fit it in. That way you wouldn't be topping with water. It also sounds like you might want to look at your general AG technique to increase your efficiency.