How to track the trajectory of your gravity through the mash process?

[Fishin-Jay]

I've seen in a couple posts people mentioning that it's better to use your refractometer to check on your gravity throughout the sparge and to "brew to hit your target gravity rather than brew to hit your target volume." Essentially they were saying it's better to have 4 gallons of beer at the right gravity rather than 5 gallons at too low of a gravity.

I agree with this sentiment, but I don't know how to tell if my gravity is going to be correct or not.

For example, I know that my system boils off 1.5 gallons per hour in the kettle and I leave .75 gallons in the kettle with the trub. So, if I want 5.25 gallons in my primary I need to start with 7.5 gallons of wort, boil for one hour down to 6 gallons, then transfer to the fermenter.

In the same scenario if I want 6 gallons of 1.080 wort remaining after the boil, I need my preboil gravity to be 1.064 at 7.5 gallons.

My question is this: As I am fly sparging and my volume is at 5 gallons, what should my gravity be if I am going to hit 1.064 at 7.5 gallons? Since the wort gravity coming out of the mash tun is continuously decreasing (ie the first few drops out of the tun are higher gravity than the last few drops), how can I tell if I'm going to hit my target while I'm mid-sparge?

 

[Fishin-Jay]

That's why in fly sparging it's important to keep an eye on the gravity of the runnings. When the gravity decreases, the PH increases. I believe the general rule is stop sparging when gravity drops below 1.010.

I just saw this from "steve-o" in another post. Is this the rule of thumb I'm looking for?
He was talking about the ph increasing and getting too many tannins in the beer, but it might be a good stopping point for any fly sparge regardless of whether or not I've hit my target gravity.

 

[david_42]

Yea, 1.010 is the point of diminishing returns.

 

[lschiavo]

My question is this: As I am fly sparging and my volume is at 5 gallons, what should my gravity be if I am going to hit 1.064 at 7.5 gallons? Since the wort gravity coming out of the mash tun is continuously decreasing (ie the first few drops out of the tun are higher gravity than the last few drops), how can I tell if I'm going to hit my target while I'm mid-sparge?

This sounds like it would require a very involved calcuation that would likely be different for every brew.

I think the best thing as homebrewers is to shoot for is consistency. If you are off on one batch, make adjustments to that one and corrections to your process for the next. That is my philosophy anyway.

 

[Fishin-Jay]

Thanks for the replies. 1.010 it is then! If I haven't reached my desired preboil volume by the time the wort reaches 1.010 I'll stop the sparge where it is and go with what ever I've got. (Adjusting hops utilization accordingly of course)

 

[IrregularPulse]

Thanks for the replies. 1.010 it is then! If I haven't reached my desired preboil volume by the time the wort reaches 1.010 I'll stop the sparge where it is and go with what ever I've got. (Adjusting hops utilization accordingly of course)

I've always seen, sparge until your volume or 1010, which ever comes first. Then you can top up to volume with water. Not water ran through your grain, just water. But I suppose this comes down to which is more important to each brewer. Hitting volume or gravity. Me personally would rather have a extra 1/2-1 gallon of slightly lower ABV beer.

 

[JVD_X]

I find with fly sparging that I will often exceed my targeted collection volume well before I get to 1.010

What I usually do is go all the way to 1.010 regardless of collected volume. Since I use beersmith I will bump the efficiency up and this will prevent me from overshooting next time.