Homebrewers Association  AHA Forum
General Category => All Grain Brewing => Topic started by: Beer Monger on May 02, 2011, 03:44:05 PM

Someone help me with the math here.
If I'm brewing a 5 gallon batch and want an OG of, for example. 1.060, how much should I expect my OG to drop if I wind up with six gallons of wort isntead of 5?
I guess the basic question here is, if you have wort that's 1.060, what would the reading drop to if you added a gallon of water?

Easy....5 gal. at 60 gravity gives you 300 gravity units (5*60+300). If you have 6 gal., it becomes 300/6=50. So the gravity would be 1.050.

Easy....5 gal. at 60 gravity gives you 300 gravity units (5*60+300). If you have 6 gal., it becomes 300/6=50. So the gravity would be 1.050.
OK. Thanks, Denny. That would partly explain the lower OG on my batch this weekend. I think I wond up with 6 gallons instead of 5. I must have overcompensated for the losses I was experiencing when doing 10 gallon batches (the batch this weekend was 5).

To make it even more simple: gravity is points/gallon, so if your volume increases by the ratio 6/5, your gravity lowers to 5/6.
Now, you might get a little bit higher efficiency from the longer sparge, but that will be small compared to the loss of 16.66667% due to dilution.

Easy....5 gal. at 60 gravity gives you 300 gravity units (5*60+300). If you have 6 gal., it becomes 300/6=50. So the gravity would be 1.050.
OK. Thanks, Denny. That would partly explain the lower OG on my batch this weekend. I think I wond up with 6 gallons instead of 5. I must have overcompensated for the losses I was experiencing when doing 10 gallon batches (the batch this weekend was 5).
Just curious... why do you think you'd get greater losses in a 10 gallon batch? Things like mash tun and boil kettle dead space, as well as boil off, should be a fixed volume and not proportional to your batch size, so you'd have less loss in a 10 gallon batch as a percentage. Unless you're using different equipment, that is.

I can think of one situation where the (lautering) efficiencies would be different between a 5 and 10 gallon batch, and a lowgravity versus a highgravity batch, especially with a round 10gallon Rubbermaid/Gott cooler due to grain bed compaction. There is just too much height to the grain bed given its base. You can still get the sparge done, but it takes a lot longer. If you're regularly doing large batches and/or high gravity brews, go for the bigger and rectangular cooler in order to keep the grain bed height low relative to the base.

Easy....5 gal. at 60 gravity gives you 300 gravity units (5*60+300). If you have 6 gal., it becomes 300/6=50. So the gravity would be 1.050.
OK. Thanks, Denny. That would partly explain the lower OG on my batch this weekend. I think I wond up with 6 gallons instead of 5. I must have overcompensated for the losses I was experiencing when doing 10 gallon batches (the batch this weekend was 5).
Just curious... why do you think you'd get greater losses in a 10 gallon batch? Things like mash tun and boil kettle dead space, as well as boil off, should be a fixed volume and not proportional to your batch size, so you'd have less loss in a 10 gallon batch as a percentage. Unless you're using different equipment, that is.
I don't think I'll get greater losses in a 10 gallon batch. I don't believe I said that.
The last few batches I made (which were 10 gallon batches), I was coming up a bit short. What I was saying is that I must have overcompensated for equipment losses (by adding too much more water to the mash & sparge). So even though this batch was only 5 gallons, my overcompenstation means I wound up with over 5 gallons.
No big deal. So I have more beer that's slighly less potent.

Beersmith has a dilution calculator that seems to work pretty well also. As Denny pointed out the math is pretty easy but if you have the soaftware it's there also.

Beersmith has a dilution calculator that seems to work pretty well also. As Denny pointed out the math is pretty easy but if you have the soaftware it's there also.
Yeah, I'm just being lazy today. Had a crazybusy weekend & wish I could have stayed home in bed today. lol