One thing I’ve been able to do consistently since my AG excursion began 1 1/2 years ago is miss my FG on the low side. :( It seems that every time my fermentation is done, I find my self several points below my target. This time, I started at 1.084 one week ago and today it’s already down to 1.016. My FG should be 1.021. I dry hopped today so should I crash it to stop fermentation or let it go? Any ideas as to why I’m missing my FG?
Are you certain your hydrometer is accurate?
Temperature correction on the hydrometer?
I don’t seem to recall an issue when doing extract :-\
It was taken at 68°.
Have you calibrated your thermometer? You could be mashing cooler than you think.
1. No, I wouldn’t crash while you are dry hopping - it needs to be done @ ~ 65 - 70F to extract the best hop flavor and aroma…
2. Are your OGs consistently low too, or just FG ? If you regularly are a few points low on your OG, it would carry over to making your FG low too.
3. Yeast attenuation rates are an estimate at best - a lot of factors go into determining what your actual FG will be - grist, mash temp, yeast health, pitching rate.
4. What temp are you mashing at ? Since it seems to be an AG problem and not an extract one, I wonder about the accuracy of your thermometer. If your thermometer is not very accurate, you could easily be mashing several degrees cooler than you think. This would make a more highly fermentable wort and would give you a lower FG than you anticipated.
5. What yeast did you use? Going from 1.084 to 1.016 is 80% attenuation and would not be out of line for a number of yeasts.
I had the same trouble for a while. Are you batch sparging or fly sparging? I batch sparge and used to let my first runnings sit in the kettle while I sparged. I now turn on the flame right away and start heating my first runnings while I sparge/vorlauf/drain my second runnings. It fixed my over-attenuation problem and I get to a boil faster. Win-win!
Thermometers are calibrated. I have 5 on hand 
I almost always hit my OG and I’m using 1056 for my yeast. I did a starter because the OG was high but that’s not always the case. With this batch I was aiming for 153° but overshot to 162°. I quickly got it down to my target temp but lost a lot of heat during the mash. It got down to around 148° but I brought it back up with boiling water. Now that I think about it, it was kind of a roller coaster mash :
Funny because I do that every time! Just out of curiosity, what impact would that have?
Heating the first runnings will help to denature the enzymes. If you just let your first runnings sit while you sparge, the enzymes in the liquid will continue to work on the sugars (at a lower temp), which leads to a more fermentable wort and low final gravities… At least, this is how things go on my system. YMMV.
Good luck! I hope you figure it out!
Beersmith (and other software) will help you estimate your strike temp for mash water pretty accurately. It might stabilize your process for mashing a bit. That could be one solution. But thermometer inaccuracy could be an issue too. I use a digital lollipop thermometer (NIST traceable) that works very well :
It’s very affordable too.
+1 on the thermometer!
Thanks for all the insight! It’s about time for a new thermometer anyways so now I have an excuse
Are you looking at mash ph? That could also be an issue in the fermentability of your wort.
This is the first time I’ve used RO water and made water adjustments. I’m using pH strips for now and initially, it was in the appropriate range but when I did my sparge, I forgot to add the calcium chloride which resulted in the pH dropping a bit low.
It really sounds like you need a good accurate thermometer and getting your mash process more consistent. Always having to raise or lower the temp is not a good practice. Also, if the raising or lowering requires hot or cold water additions then you’re also screwing up all your volumes in the process as well.
As I read the responses, I get that feeling as well 8)