Nick Carr on July 24, 2020 0 Comments We can’t brew without water. It makes up 90 to 95% of every single beer made. But, water volume in the brewing process can be a tricky thing to get a handle on, especially for those just coming into the hobby. Water is lost at several different points along the road to a finished batch of beer. All of us, at one time or another, have finished a brewing day with the sudden and sinking realization that we have less than our predicted volume size sitting in front of us. When this happens you’re basically left with three options, each of them not great. You can leave it alone and be happy with a lesser volume at the right starting gravity (the best option in my opinion); add water to get you’re desired volume and lower your starting gravity; or add water and adjunct sugar of some type to get the desired volume and keep the starting gravity, but likely change the beer’s character. Knowing the places you lose water, how to calculate average losses, and then accommodate for them gives you a much better chance of hitting your targeted package volume. Water can be lost at four different points. Grain absorption Dead spaces in brewing equipment Evaporation during the boil Trub loss (hop/yeast) There is a fifth, often talked about change in density (shrinkage), but as we’ll see this isn’t really a loss unless you forget about it. All of these are going to vary to some degree, depending on your particular equipment and brewing practices. For the most accurate quantities, carefully measure water volumes and water loss over several batches. Always take detailed notes. Let’s look at some calculations and averages for each of these “places of loss.” Water Absorption By Grain There are several different, “average loss” numbers used to calculate grain absorption. One of the most prevalent is .125 gallons of water per pound of grain. In his book Designing Great Beers, Ray Daniels uses .2 gallons. Another way to look at this is: spent grain is 78 to 80% water and a measly 22 to 20 percent actual grain mass. But, these numbers don’t really help us unless we take into account that spent grain will weigh less after the mash (when spent) than before. This is something many homebrewers simply don’t know or forget to consider. Weight will vary somewhat depending on the efficiency of your system, but Daniels gives an average of spent grain weighing 60% less than it did before being mashed. Carrying this logic forward, your spent grain will weigh 40% of its original weight. Now, remember, spent grain weight is only 20 to 22 percent actual grain. The rest (78% to 80%) is water. Using these numbers we can estimate water loss. The weight in water will be close to 4 times the spent grain’s weight (80 divided by 20 is 4). Daniels gives an example of brewing with 10 pounds of grain which ends up weighing 4 pounds when done mashing: 10 pounds x .4 (or 40%) = 4. Since the water is 4 times the grain, we would multiply 4 lbs by 4 lbs and get 16 pounds of water. Then, since water weighs roughly 8.34 pounds we could divide 16 lbs by 8.34 lbs/gallon and get 1.9 gallons of water lost. This falls near the .2 gallons/lb. that Ray Daniels suggests. But, it’s .65 gallons more than if you used the .125 gallons/lb. What does all this mean? It means you need to find the number that works with your system and brewing practices. These numbers are good places to start. But, maybe you fall somewhere in the middle; .16 gallons/lb. anyone? Experiment, measure all your ingredients including your water and take good notes. Dead Spaces in Brewing Equipment You’ll never get all of the water/wort out of your brewing equipment. Pockets are left below the level of valves and in transfer lines, and again, water loss from dead space is completely tied to your particular brewing equipment. You can discover this volume by simply measuring what is left behind in the normal process of one of your brew days or you could do a “dry” run through your brewing equipment with just water, measuring the volumes wherever water is left behind. Generally, it won’t be more than a gallon and for some brewers much less. Evaporation During The Boil It’s important that you let your boil roll. That is to say, don’t turn it down to a simmer in hopes of reducing evaporation. Account for the expected evaporation beforehand. A rolling boil is important for hop utilization, getting rid of volatile compounds such as DMS, color development, etc. Water loss during the boil is dependent on the shape and size of your kettle (wider and shorter kettle = more evaporation), the heat source, even things like temperature and wind (if brewing outside) can make a difference. The Handbook of Basic Brewing Calculations, by Stephan R. Holle, uses a basic evaporation rate of anywhere from 5 to 15 percent per hour for commercial brewing, which for a 5 gallon batch of beer would look like 0.25 to 0.75 gallons. However, homebrewing systems tend to be less efficient than commercial systems and can average from 1.5 gallons/hr. all the way up to 2.5 gallons/hr. depending on the factors already listed. Generally, 1.5 gallons/ hr. is the number most often used as an average in brewing calculations. Getting a better number for your particular situation is just a matter of measuring loss on your system. To do this simply put a measured amount of room temperature water in your brew kettle and boil it for an hour. After the hour is up, cool the water down to room temperature so you don’t get a false measurement due to change in density (more about this below) and measure what’s left. Water Loss To Trub In every batch of beer a certain amount of water gets locked up in hop and yeast trub. Not accounting for this loss can cause a situation where you have to rack right down to the trub to get the right volume, which, inevitably, means more particulates get through to the next stage. It’s better to account for a certain loss and have the ability to leave a planned amount of wort behind in the kettle, ensuring you also leave behind as much trub as possible. The same goes for racking from the fermentor, where some beer will be left behind, locked in the yeast bed. The amount lost can range widely depending on variables such as dimensions of brewing vessels, amount of hops used in the boil, dry hopping, and the type of yeast used. Measuring this over a few batches will get you a ballpark for your setup, but also keep in mind it will vary somewhat between different recipes. The actual amount lost can be anywhere from half a quart to one full gallon between the kettle trub and the yeast bed. Many recipes are built from the beginning with this particular loss in mind, i.e. a 5.5 gallon or 6-gallon brew often means 5 gallons are packaged. Loss Due To Change In Density Density change, or shrinkage, can also cause water loss, or more accurately cause a false measurement. When water is heated it expands. When it is cooled from boiling down to fermentation temperatures the change in density can show as around a 4% drop in volume. But, this doesn’t matter much if you measure your water volumes at room temperature. This way you have the right volumes at the beginning. The water expands when it boils then contracts back to the original volume when it cools (minus evaporation loss, of course). Really the only time this is a concern is when measuring your hot runoff for the pre-boil volume. If your pre-boil volume is, say, 6 gallons and you stop at 6 gallons, this is a false measurement and you’ll end up with slightly less after the wort shrinks. You can account for that shrinkage here by going slightly over your 6-gallon pre-boil mark. Because your hot runoff isn’t actually boiling, expansion is less than 4%, but using 4% ensures you’ll have enough. This addition would make your pre-boil volume 6.25 gallons. Quick Reference of Average Water Loss Numbers Grain Absorption: .125 to .2 gallons per pound Dead Spaces: Up to 1 gallon Evaporation: 1.5 to 2.5 Gallons per Hour Trub: 1 quart to 2 Gallons Shrinkage: 4% of total water volume So, taking all these numbers together let’s look at a quick example. We’ll say we want to end up with 5 gallons after fermentation. Our recipe calls for using 10 pounds of malt with a 60-minute boil. Ok, let’s work it backward from our finished volume, and for the sake of simplicity, I’m going to use mid-ranges for the water losses listed above. 5 gallons [packaged] + (.16 x 10 = 1.6) [grain absorption] + 1 gallon [trub loss] + 1.5 gallons [evaporation loss] + 0.5 gallons [dead space loss] = 9.6 gallons of water Once you have the total volume you can split it between your mash and sparge. To do this you’ll need to know how thick (liquid-to-grist ratio) your mash will be. Here, I’m going to use the homebrew average of 1.25 quarts per pound of grain. So, multiply the grain weight (10 lb.) by 1.25 and get 12.8 quarts or 3.125 gallons. To this, we’d add any water loss from dead space in your mash (false bottom, etc.). Let’s use .3 gallons for dead space loss, which means we need 3.425 gallons for the mash. The remainder of the water, roughly 6.2 gallons will be used to sparge and hit the pre-boil volume. Final Thoughts Though you can get away with simply guessing at the amount of water you’ll need there’s always the chance you’ll either heat too much and waste water, or worse, not heat enough and end up in a situation where you’re scrambling to heat more. We can get close by trial and error, especially if you continually use the same system. But with a little thought, you can really dial in your needed volumes. This can be especially important if you change something in your system or are breaking in a brand new one.
