Can you calculate pre biol gravity from runnings samples?

The obvious question is why wouldn't you wiat till the sparge water is in the kettle chris? Well because it just dawned on me that I should do that next time. I was brewing my second AG this afternoon and took samples of the mash out and sparge runnings to analyse later. What I didn't do was take a sample of the mixed. So I am wondering f there is a way to calculate the pre biol SG from the samples. If it is possible I will post the recepie and dough in temps and volumes, ect...

All in all it was a better AG experience then last time. Hit the sparge temp this time, but had crazy boil off that I don't understand.

anyway all help would be appreciated.

Yup. If you know both the gravity and exact volumes of each of your runnings, you can do the math. Probably something like (og1 x vol1)+(og2 x vol2)+(og3 x vol3)/total gallons where og is just the number of "points" like 67 and not 1.067 for example.

Let's say 3 gal of 1.070, 2 gal of 1.050, and 2 gal of 1.022.
(70 x 3)+(50 x 2)+(22 x 2) = 354 total point/7 gallons = ~51 or 1.051 total OG.

If you really want to take the OG of preboil, make sure you stir it up well so you don't get stratification of varying gravities. This will usually take care of itself if you've just acheived boil, but you'll probably take the sample when the wort first hits the kettle.

cool this will atleast give me an idea of how well I did.

So I crunched the numbers and well I didn't do so good... But hey the last batch was undrinkable (tannin extract) and I think this one is going to make it to the bottles. I think I need hotter sparge water to get more out of the grains..