Post-boil gravity adjustment

[steveo929]

So for some reason or another (being a noob) I thought that the OG reading was taken before the boil. Now I realize through some research that I was completely wrong and should have been taking the readings after the boil, whether in the carboy before pitching yeast or in the brewpot and adjusting for temp.

So needless to say my OG readings have always been a little lower than expected, but still not that bad. So I'm assuming that after the boil it does increase quite a bit.

Does anyone happen to know if there's a formula to adjust my gravity readings for a 60min, 90min, etc boil? If there's no formula does anyone know how much higher I can expect the gravity reading to increase?

Thanks so much! I've learned so much on this site.

 

[kryolla]

you need to know your boil off rate then take a gravity reading pre-boil and pre-boil volume them minus your boil off rate you will get your post boil volume and with some formula you will get your OG. I have a spreadsheet so I dont know the formula off the top of my head but its in Designing Great Beer or when I get home I can get it

 

[Catch-22]

If you are using pre boil readings as your OG, your real OG will be much higher due to the concentrated wort. I calculate what my expected Preboil and Postboil gravity should be using Beersmith and adjust with DME or water accordingly. Your real OG could be as much as 15 points higher depending on your starting volume, ending volume and boil off.

 

[steveo929]

Cool, the formula would be great! Thanks guys, that makes me feel a lot better about my system...I have put a good deal of money into a killer setup and was hoping for good efficiency.

 

[Frank99]

Someone gave me this formula when I had a similar type of issue.
In your case you'll need to know your initial volume/final volume:

FinalGravity = (InitGravity - 1) * 1000 * InitialVolume / FinalVolume / 1000 + 1

 

[pkeeler]

You can take your OG before the boil, if you know how many gallons (liters) of wort you have then and how much you have at the end of the boil. If your kettle is symmetrical, it is easy to figure out how many inches from the top is how many gallons.

In fact, if you are at target OG, at 6 gal. before the boil, then you can simply add water to the fermenter to get to 6 gal. Marking gallons on your fermenter helps Lets say you measure your boil kettle and you have 6 gal. at 1.050, but you want 1.055. You know that if you put 5.5 gal. in your fermenter it will be at target.

But...it will be off somewhat because of hops and break material. But it is something to fall back on if you forget to take OG during the heat of battle and don't remember until after you have buttoned up the primary.

 

[steveo929]

Cool, thanks everyone