Water: How much is enough?

by Ray Daniels

(This article is extracted from Daniels' book entitled Designing Great Beers, available from Brewers Publications beginning in December 1996.)

For years I didn't bother calculating how much water I needed for a brew. I would just heat up some water, treat it and use however much I needed. Of course I sometimes ran short and had to make up some more real quick.

After awhile I learned that lesson and made up a lot of water in advance so I would never run out. When it came time to sparge, I just pumped and pumped that water in there, collecting everything that came out. What happened then is that I usually had twice as much wort as I needed. This led to long boils, wasted time and energy, etc.

Finally, I learned how to calculate the amount of water that would actually be needed. It saves time by making the whole brewing process more efficient. Then too, I can calculate my water salt additions in advance to match the quantity of water. All of this avoids mid-brew confusion and crisis and makes the brewing day a lot more pleasant.

OK. Some pretty good reasons for calculating water quantity. But if you're like me, you just won't do it if it is too complicated. Let's see if we can keep it simple.

The total quantity of water you need for brewing includes five items. The first one is the finished beer! If you are making five gallons of beer, you've got to use at least five gallons of water.

Beyond the final wort volume, all the other water you add is lost somewhere in the process. Generally, these losses can be categorized into four types. They are:

Water trapped in the spent grains
Water evaporated during the boil
Water left behind in equipment, hoses, etc.
Shrinkage of the hot wort as it cools

Let's go through each of these items, discussing how they would be calculated before we do an overall example.

During mashing, the grains absorb a lot of water that can not be drained out in the lauter tun. As it turns out, the weight of the water trapped in the grains is predictable. The total weight of the spent grain mass is 20 percent grain and 80 percent water.

Simple, right? The only thing you have to remember is that the weight of the grain after mashing is not the same as the weight of the grain you weigh out to go in the mash. During mashing, you extract sugar and protein from the grains and that leaves them a shadow of their former self. While you can calculate this more precisely for each batch if you really want to, it is safe to assume that the post-mash grain mass is about 40 percent of the weight of the grain you added.

So, if we mash 10 pounds of grain, it will weigh about 4 pounds when you are finished. Since this 4 pounds is 20 percent of the weight of the spent grains, the weight of the water will equal four times the weight of the grain. (80 percent divided by 20 percent equals 4.) Thus, you will lose 4 x 4 pounds or 16 pounds of water in the spent grains. Since water weighs about 8 pounds per gallon, this equals two gallons.

Once you do this calculation once or twice, it can become second nature. But I know that many people don't get to brew as often as they would like, so Table I shown below gives water loss based upon the weight of the grain you mash. If you work with larger amounts of grain (or simply prefer to use an equation rather than a table), you can predict the amount of water retained by the grains by the following equations:

Grain weight x 0.2 = Gallons of water retained by grains
or
Grain weight x 0.0064 = Barrels of water retained by grains

Table I: Gallons of Water Lost in Spent Grains


Pounds	  Gallons	Pounds	  Gallons

of Grain  of Water  	of Grain  of Water

Mashed	  Lost  	Mashed	  Lost  

3	  0.675		15	  3.25

4	  0.875		16	  3.5

5	  1		17	  3.675

6	  1.3		18	  4

7	  1.5		19	  4.125

8	  1.75		20	  4.33

9	  2		21	  4.5

10	  2.125		22	  4.75

11	  2.375		23	  5

12	  2.5		24	  5.25

13	  2.75		25	  5.5

14	  3

Evaporation losses are usually calculated on the basis of an accepted hourly rate of evaporation, multiplied by the length of the boil. For homebrewers, this can vary rather widely depending upon the amount of wort you boil and the heat source. If you really want a good number to go in here, you can run a little experiment to determine the actual rate of evaporation on your system. In the meantime, you can work with the figure of 5 percent per hour, which is based upon big brewery experience.

By the way, if you plan a decoction mash, don't forget to figure in some additional water to account for evaporation during the boiling parts of the decoction.

The water left behind in equipment is a figure that you can probably determine on a one time basis. This is the stuff left in the bottom of a vessel, in tubing or mixed up with debris that you can't actually move on to the next step in the process. In many homebrew setups this number is pretty close to zero. But before you assume that, really think about your process step-by-step, remembering where you find left over liquid as you go through a brew. In larger setups, you may want to collect all your losses during one brew in order to develop a good estimate of this number.

In my homebrew setup there are two main losses. First, my mash/lauter tun has a substantial dead space below the wort outlet, this accounts for about a half gallon of loss on each brew. Next, I lose about two quarts of sparge water in the holding bucket that I pump from and in the tubing that runs to the mash tun. Based on these two sources of water loss, I add an extra gallon to my water needs for every batch.

We also need to account for losses in trub and hop debris, but here it makes more sense to adjust the volume you target at the end of the boil. Although my fermenters are generally five gallon carboys, I try to hit 5.5 to 6 gallons at the end of the boil. This way, when the wort is chilled and I have siphoned the clear wort off of the trub and hop debris, I get the right amount of wort to fill my fermenter.

Finally, we have shrinkage. This is the change in density, and therefore volume, when water cools from boiling to 68 deg F. This value is 4 percent.

Now that we have all the pieces, let's work and example to see how easy this can be.

Let's assume we are making five gallons of pale ale on my system, using 8.5 pounds of grain. We'll target 5.5 gallons at the end of a 90 minute boil.

Batch size:

5 gallons



Final Boil Volume:	

5.5 gallons	(Trub and hop debris losses.)



Shrinkage:

Divide by 0.96	(Accounts for 4% shrinkage.)



Evaporation:

Divide by 0.925	( = 1 - (evap rate x boil length))



Equals: Runoff volume of

6.2 gallons     (Volume in kettle when boil starts.)



Equip Losses:

Add 1 gallon	(My system value.)



Spent Grain:

Add 1.875	(From Table I.)



Total Water

Required:

9.075 gallons

Once you have this figure, you can easily determine the distribution between mashing and sparging. Multiply your grain weight by the ratio of water with which you will mash. In this case, we'll use 1.33 qts/lb, giving us 2.8 gallons of mash water. If your mash tun has a false bottom like mine does, you'll need to add enough water to fill the space below the false bottom. In my case, this volume is one gallon, so I would use 3.8 gallons of water in the mash process. The remainder of the water -- about 5.25 gallons in this case -- will be needed for sparging in order to ensure that you get adequate volume in the boil kettle.

This procedure is really quite simple and will prevent a lot of confusion during brewing. To make it as easy as possible, use the blank work sheet shown below.

Water Volume Calculation Worksheet

Batch size:

_____ gallons



Trub & hop debris losses:

Add: _____ gallon  (0.5 to 1 gallon)



Final Boil Volume:	

_____ gallons      (Trub and hop debris losses.)





Shrinkage:

Divide by 0.96     (Accounts for 4% shrinkage.)





Evaporation:

Divide by _____    ( = 1 - (evap rate x boil length))





Equals: Runoff volume

_____ gallons      (Volume in kettle when boil starts.)







Equip Losses:

Add _____ gallon   (Your system value.)





Spent Grain Losses:

Add _____ gallon   (From Table I above.)





Total Water Required:

_____ gallons