Surprisingly low OG on an Imperial Stout extract kit

So I just brewed the Imperial Stout extract kit, which calls for an OG of 1.086. The fermentables are simply 2 6lb jugs of Dark LME and a small bag of steeping grains. Somehow though, my OG only hit 1.076. I’m having a hard time determining where the deficit could’ve happened. I’m fairly new to brewing (I think this was batch 10) and I know OG isn’t always going to be exact, but it’s always been close and 10 entire points seems extravagant. No wort was spilled, Oxygenated/mixed a solid 5 minutes before taking sample, and it was topped up to exactly 5 gallons. Any thoughts? Can the LME perhaps get old and lose potency somehow? I doubt that, but I can’t really think of any good explanations.
Also, I decided right after I pitched the yeast to try to bump it up a little and added a 5 oz package of dextrose (only thing I really had sitting around) straight into the carboy. How much of a gravity increase can I expect from that? Poor decision? Again, I’m pretty green yet so bear with my relative ignorance.

It’s possible you experienced stratification in the wort. So the reading you took may have not been as mixed or homogenized. This happens often when brewing extract and topping off with water.

5 oz of dextrose won’t have much of an effect at all. Just let it ride as is and I’m sure the beer will turn out just fine

Had it had a chance to sit and stratify for awhile I’d think that a possibility, but i’d shaken the bejesus out of it for a good 5 minutes right before taking the sample. It was about as mixed as anything could ever be.

If it was topped up to exactly 5 gals and you used all the extract then it is impossible to miss the OG. You would be surprised at how difficult it can be to get it to mix 100%.

I had a similar problem with low OG on the Imperial Stout. Being new to brewing, this is my 6th kit and the first time I have seen a lower OG than advertised. Mine came out 1.066 instead of 1.086. I had about 5.5 gallons of finished wort and used a complete boil, so no water was added to the fermentation vessel. The only thing I did differently was added 2 packs of yeast. I had the Safale 05 that came with the kit and a pack of Safale 04 that I added. I started both a couple hours before pitching. My fermentation took off immediately and the airlock blew off the first night. I sanitized it and put it back in the next morning and it was bubbling ferociously the rest of the day, then suddenly stopped bubbling. I have not opened it since. The krausen has fallen on day 2 and there are no bubbles. Temp has been higher than I like at 75 by late afternoon. That drops to a low of about 66 at night.

Any suggestions/observations that minght lend to a better understanding of what happened on my part? Thanks.

The OG reading on an extract kit is usually due to stratification, or not mixing the wort, but if you did a full boil it should be mixed. I’d guess the extra .5gl lowered the OG. As for the aggressive ferm, at an ambient temp of 75, +the heat generated by the yeast you were probably around 80+. That’s why it took off so aggressively and subsided so fast. I do not think it’s done yet, though. For a big beer like that I would leave it for no less than a month in the fermenter.
You may want to look into temp control (such as a cheap swamp cooler, or a wet towel wrapped around your fermenter with a fan blowing on it). With your temps being that high, you are more than likely to get some undesirable flavors (very aggressive alcohol taste right up front).
Also, let this beer age for quite some time to let it round out the corners and for the flavors to meld.

Namaste!!! :cheers:

Thanks for the reply. I was planning on adding bourbon soaked oak chips in a couple weeks and was going to let this one sit for at least 6 months. Hopefully that amount of time will balance out any abrupt up-front alcohol taste.