Ask Mr. Wizard

Wort Volume


Thomas A. Adamczak • Grand Rapids, Michigan asks,

I have been homebrewing for more than a year and a half. I’ve mainly been extract brewing with great results, but I have reached that point that every homebrewer has reached, or will reach: the need to move on to grain brewing. Almost every grain recipe (partial mash or all-grain) suggests bringing the volume of wort to six gallons before boiling, even if the runoff after sparging is less than six gallons. Typically in an extract batch I use two to three gallons of water to boil my wort, then add enough pre-boiled and cooled water to bring my volume to five gallons prior to pitching.

What effects could boiling an all-grain or partial mash wort at a volume of less than six gallons have on my overall batch if I were to add preboiled tap water to the wort (to five gallons) prior to pitching? It seems the pre-boiled, cooled water would help cool the wort quicker to pitching temperature.


This question really has more to do with sparging than it does with the volume of wort to boil. An all-grain brew begins with the mashing process. During mashing, starch is converted to fermentable sugars. A good portion of the sugars are released into the liquid portion of the mash and create wort, but many of the sugars stay trapped in the malt particles. When wort run-off begins, the first wort that flows from the grain bed is the wort outside of the grain particles. In winemaking, this would be termed the free-run and represents the highest quality must (wine’s equivalent of wort) flowing from the grape. Winemakers press the juice out of the grape, and brewers rinse the malt sugars from the grain bed by sparging. In both cases the objective is to increase yield.

Most brewers sparge long enough to rinse most of the extract from the grain but stop sparging when the wort gravity drops below about 1.008 specific gravity. Some brewers measure wort pH as it flows from the grain bed and stop collecting wort when the pH approaches six. The reason for rejecting high pH and low specific gravity wort (the two cases usually correlate well) is that unwanted materials begin to dominate the composition of wort. The last runnings from the grain bed will contain more tannins (polyphenols) than fermentable sugars if too much weak wort is collected. This can give beer an astringent mouthfeel. As a rule of thumb, it’s time to stop sparging when the wort ceases to taste sweet and begins to taste like a weak cup of tea.

In a controlled system where everything relating to extract yield (malt milling, mash temperatures, mash thickness, sparge temperature, grain-bed thickness, wort flow rate from the grain bed, and so on) is held constant brew after brew, the point at which wort collection stops is fairly constant. This is why many commercial breweries collect a constant volume of wort in the brew kettle for a given recipe.

Homebrew recipes always should be read with a grain of skepticism, because the author of the recipe may have different equipment than you do. When I use another brewer’s recipe, I follow the ratio of malt specified in the recipe and use the recipe’s hopping schedule, but that’s about it. I have my own preferences regarding mash thickness, sparging technique, and fermentation practices. I view recipes as a general guide. If a recipe says to collect six gallons of wort, I read that as somewhere around six gallons depending on when the wort gravity drops below my own benchmark of quality. The main goal I try to hit relating to the recipe is wort original gravity, because that has a big influence on beer flavor.

Another variable to watch with respect to wort volume is hopping. If the recipe calls for 2.5 ounces of hops for a five-gallon batch and you end up with 2.5 ounces in a four-gallon batch, be prepared for more bitterness than the recipe describes.

The bottom line is if you get all the extract out of the grain before hitting six gallons, then you’ve done well. In fact if you get a good yield, you may have to add water to dilute the wort gravity down to the gravity called for in the recipe. You may also have to use more hops to get the same bitterness because of the increased wort volume. In most cases this tweaking will be minimal and you probably will end up collecting somewhere between five and six gallons of wort to get all the sugar out of the grain bed.

If you collect less wort than specified by the recipe, the wort you boil will be a higher specific gravity. This means you may get a little more wort darkening during the boil and your hop utilization will probably go down a bit. If you then add water at the end of the boil to bring the volume up to five gallons, the wort gravity will most likely be low because that water should have been used to rinse the goodies from the grain.

There are commercial brews that actually sacrifice extract yield for flavor (imagine that!). One notable example is Kirin Ichiban. Ichiban has several slightly different meanings in Japanese, but in vague terms it means “first” and is often used to denote premium quality. Kirin Ichiban beer is made by collecting just the first wort or “free run” from the grain, and the wort gravity is diluted to a normal level with water. This practice eliminates all the “nasties” potentially extracted from the grain during sparging but in the process reduces the wort volume yield from the grain. Kirin markets this brewing practice in the same way many wineries market using only “free run” must for their wines. If you did this at home, a five-gallon recipe would turn into a three-gallon batch or you could use about 12/3 times the amount (five-thirds more) grain and produce five gallons of wort post-dilution.

I’m not sure what type of answer you were in search of, but hopefully I have addressed your concerns. Kampai!

Response by Ashton Lewis.