How much water do I need?


For new brewers, it’s often easy to get overwhelmed by the glut of information available online. Experienced brewers will read grain bills and magically turn it in to beer. They’ll provide recipes that give a list of grain in pounds or kilos and rarely tell you how much water to add, or when. This is because each brewer adapts the amount of water to their specific system, which requires a bit of trial and error to figure out. So here’s a handy explanation of water additions and how they fit into the brew process.

The first thing to decide is whether you’re doing a full-boil or partial-boil mash. A full-boil mash is simpler, but less efficient. It also requires a very large mash tun as both the grain and all the water need to fit. Many Brew-In-A-Bag brewers do full-boil mashes.

Partial-boil mashes are often used with the traditional 3 kettle set-up with a dedicated mash tun, a hot liquor tun and a boil kettle.

Strike water

Strike water is the initial amount of water you add to the grain in order to reach your rest temperature. It’s probably the easiest amount to calculate, because it’s simply a ratio based on how much grain you have. I like to do thick mashes as I don’t have to pump them between the mash tun and the lauter tun like commercial breweries do, and it’s more efficient and protects the enzymes against both pH and temperature changes. My ratio is 1.2 qts/lbs, (or 2.5L/kg) That means if I have a grain bill of 10 lbs, I need to add 12 qts of water. The rest remains in the hot liquor tun until the conversion is complete.

Sparge water

For those beginners, let’s go over sparge vs lauter. Sparge is water (aka liquor) that is poured into the mash tun after conversion is complete. Lauter is wort that comes out of the mash tun and goes into the kettle to be boiled. The beginning of the lauter is the strong worts flow – the wort hasn’t been diluted and is probably somewhere around 1.080-1.090 in gravity. As the lauter continues and sparge is added, the gravity decreases. Sparging rinses the sugars that aren’t carried away during the strong wort flow. If you are doing a full-boil mash, you won’t do a sparge.

The amount of water you use to sparge can’t be determined yet because there a few other things you need to know first – your grain adsorption rate and your evaporation rate

Grain adsorption rate

How much water is your grain going to adsorb? This is an important number because it determines how much wort will be lost after your mash is complete. For me, my grain adsorption rate is 1.35 fl oz/oz. That means in one pound of grain, I will lose 21.6 fl oz. because 1 qt contains 32 fl oz. (If you’re using L and kg, it’s 1.31 L/kg.) This means that for a 10 lbs grain bill, you will lose 216 fl oz, or 6.75 qts. For the same amount in L/kg, it’s 4.54 of grain, and you lose 5.94 L. This seems like a lot, and it certainly is compared to your initial strike water, but compared to your total volume, it isn’t really.

To determine how much water your grain will absorb, you simply need to measure out one pound or one kilogram, depending on which system you’re using. Add a known quantity of hot water, let’s say 2qts or 3L, wait for an hour and then drain off the amount of liquid without squeezing. Subtract the amount of liquid you get from the amount you initially added and you’ll have your grain adsorption rate.

Keep in mind that certain malts will have different adsorption rates, particularly torrified or rolled grains.

Evaporation rate

Lastly, you need to determine your evaporation rate. This rate can change based on a few factors, including the shape of your boil kettle and the power of your heating method. Your altitude is also going to affect the temperature at which water boils (as well as a great many other things not covered here).  This is best calculated by simply brewing a batch and seeing how much evaporates in one hour, then using that as your hourly rate.

Now that you have all these figures, calculating how much water you need is simple:

Amount you want to end up with + (evaporation rate per hour x hours) + (grain adsorption x amount of grain)

So if I want to end up with 5.5 gallons in the fermentor and I lose 1 gallon per hour and I boil for 1.5 hours and my grain is going to absorb 1.35 fl oz per oz and I’m using 10 lbs of grain, the numbers are:

5.5 gal +

(1 lbs x 1.5 hours) = 1.5 gallons +

(1.35 fl oz x 16 oz x 10 lbs) = 216 fl oz, converted to gallons = 1.7 gallons =

5.5 + 1.5 + 1.7 = 8.7 gallons.

In practice, this assumes that you aren’t counting any losses to trub or hops. Experimentation is going to be needed for this because it depends on a bunch of factors, including how much protein makes it into your kettle, and how comfortable you feel about sucking some of that trub into the fermentor. A good figure to start with, however, is between 3/4 and 1 gallon lost to trub, and then calculating an additional 12 fl oz per oz of hops, or in metric, 3-4 L of trub and 12 mL per gram of hops.

To my original figures, I'll estimate on the high side and calculate an extra gallon of trub (I don't like trub in my fermentor), which puts me at 9.7 gallons, and then an additional 24 fl oz for 2 oz of hops. That puts me at 10 gallons even for a basic, 10 lbs grist with 2 oz of hops. 

Your figures may not be 100% accurate to start, but they will be close enough that you don't end up ruining your first few batches while you figure out the ins and outs of your system, and as John Palmer says, "relax, don't worry about it, have a home brew".