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One of the biggest hurtles of going all-grain can be the task of determining how much water you need for your mash. But when it comes down to it, it’s pretty simple. All you need to know is how much water you:

• Use
• Waste
• Boil off

This all occurs while you’re mashing, boiling, cooling, transferring and bottling.

If you add too much water, you’ll get a lower OG than you planned. Too little and your OG will be high or you won’t have a lot of beer in your fermentor.

If you want to go the easy route, use brewing software. I feel that most are a little off. Or at least have been for my system. So I’ll draw this out the long way if you’re in the same boat – or you just like to visit the Curiosity Shoppe.

First let’s do a few experiments to find your constants.

Constants

In order to find out how much water we need, the first thing we need to figure out is how much we lose along the way during brewing. More importantly, YOU need to find out how much YOUR system loses along the way as everyone’s brewing system is different.

Grain Absorption

This can vary depending on your setup, grain crush ratio, if you stir or not, etc. But on average, you lose .2 gallons of water per pound of grain. Start here and keep track of your volumes for a few batches to get a more accurate picture of your absorption rate. Once you nail this, you’ll have a more accurate picture of how much water you need to add to your mash.

Dead Space

So there’s another area of loss – dead space in your tun. This would be if you have a false bottom or a manifold. You can measure this by draining your mash as you normally would, remove your grains and then measure what’s left in the tun.

Adding it all up

 Let’s say I have 10 lbs grain and a sparge of 3.5 gals. I collect 2 gals in my first runnings and end up with .3 gals left in my tun. Let’s apply this formula:

 Sparge Volume – First Runnings Collected – Dead Space = Grain Absorption

OR

3.5 – 2 – .3 = 1.2

So my grains absorbed 1.2 gals and my tun makes me lose .3 gallons.

If I do this now I have a base line. I can adjust my next batch to take into consideration these loses so I can add a little extra and end up closer to my targeted OG and volume. Keep track of this over time and see if your consistent with these or if you need to still slightly tweak. A perfectionist job is never done.

Kettle Loss

Now that the mash is out of the way, on to the boil and more loss. Loss of volume in the boil is unavoidable, however it can be minimized. Having a less vigorous boil can trim down evaporation a bit more than a raging boil. I’ve heard of people putting a lid on their kettle and leaving it cracked so it doesn’t boil over. While this might help with evaporation loss, I don’t recommend it as it traps DME precursors in your wort that would normally have been carried off in the boil. A little volume loss is a small price to pay for better tasting beer.

On average you lose 5%-10% per hour of boil. You can easily track your by using this formula:

Evaporation Percent = 100 – (post-boil volume * 100 / pre-boil volume)

(note: this is for a 60 minute boil longer boils will lose more)

Shrinkage

Not as uncomfortable as it sounds. But liquid loses density (thus volume) when it cools. From 212 degrees (boiling) to 60 degrees, you’ll lose 4%.

Trub

This loss happens twice. Once in the kettle and once after primary fermentation (maybe again in the secondary but I’ll get to that in a sec)

In the kettle all the cold break, hop matter and anything else that doesn’t make it to your fermentor is a loss. Just subtract the volume of trub from the amount that makes it to the fermentor and you’ll have your trub loss in the kettle. I usually lose about .2 gallons (but I only brew 3 gals at a time so use less hops)

Second trub loss is in the primary. As you rack to the secondary, you’ll want to leave behind as much of the dead yeast and other sediment that’s settled in your primary. You can lose up to .5 gal here. So again, subtract what’s left in your primary from your total that was in there and you’ll have what’s left in the secondary.

This one might not be typical, but if you’re dry hopping, adding fruit or anything else to the secondary, there will be some absorption there as well. You know the drill, subtract what’s in the secondary from your bottling bucket

Total Water Needed

OK now let’s put it all together starting with kettle loss

 ((Final Volume + Loss to Trub) / Shrinkage Factor) / Evaporation Loss Factor) = Kettle Loss

Now let’s factor in mash loss which is everything from this formula

Sparge Volume – First Runnings Collected – Dead Space = Grain Absorption

And finally anything lost in your fermnetors. So our final equation is

Kettle Loss + Dead Space + Grain Absorption + Total Fermentor Loss + Water Needed for Recipe = Total Water Needed

And that friends, is everything you’ll ever need to calculate how much water you need for brewing.