Beer Forum

Is there a way to calculate approximate og from 2nd runnings? I plan on mashing 6.5 gallons of 1.007 (pre-boil) wort for a barley wine using 21# of 2-row expecting 72% percent efficiency. I'd like to have an idea of what I might still get out of the grains before drafting a 2nd runnings recipe. Only mashing base grain to max-out my mash tun; all specialty malts will be steeped. I'd like to brew a second 5.5 gallon batch of something in the 1.060 og range and am willing to bump up og with a little dme if necessary.

Since every system is different, I'm not aware of any such universal calculations. If you did it on the same system the same way a handful of times you could probably begin to predict how your system is going to react.

Right on Ozwald. I guess another way to look at it is if I'm expecting 72% efficiency from my 1st runnings would it make since that the most I could expect would be 28% from the 2nd runnings? Logically that would make since, right?

No, it doesn't work like that. Figure it out more like this:

1) The first batch, you are doing no sparge, just collecting first runnings and that is it. Typically you'll see efficiency from 50-55% for that, forgetting that this is a partigyle and pretending this is just a no-sparge beer.

2) Then the second batch, which is really the sparge, you collect whatever is leftover. So if your normal efficiency would be somewhere around 72%, then your efficiency here is the other 72-52 = 20%. Only if you sparge a second time and then just plan for a really long boil, you can do better than that, close to 30%.

These numbers are all theoretical but should get you into the ballpark.

Kai Troester (braukaiser.com) has a page describing the physics for extraction in a batch sparge or parti gyle, along with a convenient spreadsheet to take care of the math. I have used it for batch sparging and find it to be quite accurate. You may have to make some small adjustment for fly sparging on your own system, but I expect it will do a good job there as well.

I just posted yesterday with some questions on the topic of what you actually get with the later runnings. I measure gravity and volume of my final runnings, make a correction to the gravity for expected boil evaporation, then decide how much DME to add. It requires some simple math, but that never scares me.

You may be able to find a way to do it in your software. If you can make a reasonable color estimate of the runnings you can use a similar procedure to estimate the final color of the wort.