# Calculate Original Gravity when adding water to batch after chilling wort

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#### Wil Prim

##### Beer Breath
I am trying to calculate what the original gravity of my brew will be taking into account the fact that I will be adding water to my batch before pitching the yeast to top off up to 5 gallons. The formula I have been using from the How To Brew book I am reading by John Palmer is:

mass of extract x PPG = gravity points x volume of wort

now my question is, do I take into account the water I will be adding post chilling (5 gallons) or do I use my boil amount ~ 3 gallons?

Also, the extract I am using is called muntons light LME. Is the PPG going to be 1.036? (36 for sake of formula)

Thanks in advance! This is also my first post

#### balrog

##### Supporting Member
HBT Supporter
You use total sugar added and total volume ended up with to calculate OG into fermenter.
36 is the correct rough number to use per pound of LME

using 6 pounds LME in 5 gallons therefore would give you 6 * 36 points / 5 gal = 216 total pts / 5 gal =~ 43 or OG of 1.043

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#### Wil Prim

##### Beer Breath
You use total sugar added and total volume ended up with to calculate OG into fermenter.
36 is the correct rough number to use per pound of LME

using 6 pounds LME in 5 gallons therefore would give you 6 * 36 points / 5 gal = 216 total pts / 5 gal =~ 43 or OG of 1.043

Thanks for the reply! So, you do account for the water you add after boil and chill? Is there any benefit of adding water before boil rather than top off before pitching yeast?

#### Yooper

##### Ale's What Cures You!
Staff member
Mod
HBT Supporter
In general, the more you can boil, the better. It increases hops utilization, reduces excess maillard (browning) reactions, etc.

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#### Wil Prim

##### Beer Breath
In general, the more you can boil, the better. It increases hops utilization, reduces excess maillard (browning) reactions, etc.

Okay cool, and it doesn't have an effect on final alc? or og?

#### balrog

##### Supporting Member
HBT Supporter
When using extract, you are adding all the sugar points you are going to get, and they do not (we're talking macro level here, not atomic) boil off.

So if you add 216 points, and boil 3gal, 4gal or 6gal, you still have added only 216 points. The volume of water ending up in the fermenter divided into that 216 points, will be your OG. That OG will affect the final alcohol by volume, depending on the final gravity.

#### kh54s10

##### Supporting Member
HBT Supporter
I am not really understand why you are calculating. Are you trying to determine how much water to use? If not just add the water, mix it up really well then take your OG reading.

Alcohol can be determined from your OG and final gravity readings. I use this calculator: https://www.brewersfriend.com/abv-calculator/

Or do the math: ABV = (OG - FG) * 131.25. ABV = alcohol by volume, OG = original gravity, and FG = final gravity.

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#### Wil Prim

##### Beer Breath
I am not really understand why you are calculating. Are you trying to determine how much water to use? If not just add the water, mix it up really well then take your OG reading.

Alcohol can be determined from your OG and final gravity readings. I use this calculator: https://www.brewersfriend.com/abv-calculator/

Or do the math: ABV = (OG - FG) * 131.25. ABV = alcohol by volume, OG = original gravity, and FG = final gravity.

I am just trying to see how much water to use and how that affects the alc content in the end (the og). My recipe is saying to only boil 2.5 gallons of water and then top off to 5 gallons before pitching. This seemed low to me and weird.

#### kh54s10

##### Supporting Member
HBT Supporter
I am just trying to see how much water to use and how that affects the alc content in the end (the og). My recipe is saying to only boil 2.5 gallons of water and then top off to 5 gallons before pitching. This seemed low to me and weird.

If you are doing a kit or a good recipe, that is the normal procedure. You boil the 2.5 gallons, cool it, top up to 5 gallons then take your gravity reading. If you use all the ingredients and end up with 5 gallons in the fermenter your OG will be within a point or two what the kit says it will be.

There is no need to make any calculations on how much water to use. You need to use what will give you 5 gallons going into the fermenter.

#### VirginiaHops1

##### Well-Known Member
I am just trying to see how much water to use and how that affects the alc content in the end (the og). My recipe is saying to only boil 2.5 gallons of water and then top off to 5 gallons before pitching. This seemed low to me and weird.

It's called partial boil(boiling only part of the water being used). Instructions for most 5 gallon kits tell you to do it this way because they assume people are doing this in their kitchen, where they don't have the ability to boil 6 gallons of water for a 5 gallon batch. So you have to top off to get there. As another poster said, the more you are able to boil the better though and just top off with less.

If you ever end up doing a full boil though and not topping off you'll have to have some idea of what your boil off rate is though, to try to hit the final ferment volume you're shooting for. But you can figure that out by trial and error(I did).

#### ncbrewer

##### Well-Known Member
In general, the more you can boil, the better. It increases hops utilization, reduces excess maillard (browning) reactions, etc.

If you change the boil volume, keep Yooper's post in mind. You would need to adjust the hop additions to keep the bitterness as-is.

#### DVCNick

##### Well-Known Member
Is that why my partial boil extract kits so far have come out darker and less hoppy than the description and pictures would seem to suggest?

#### kh54s10

##### Supporting Member
HBT Supporter
Is that why my partial boil extract kits so far have come out darker and less hoppy than the description and pictures would seem to suggest?

Darker is somewhat normal with extracts. They are almost always darker than an all grain version of the same. Has to do with the making of the extract and then boiling again with steeping grains.

One way to combat dark color is to add 1/2 the extract at the beginning of the boil and the rest at the end.

Less hoppy depends on how different your boil volume is compared to what the kit was designed for. I did a full boil of an extract kit once and did not notice much difference.

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