Dear Mr. Wizard,

I am looking for a formula and instructions for calculating extract efficiency in all-grain brewing. How important is it to calculate this number? I hear other brewers claim they got 75, 80, even 90 percent extract efficiency from their all-grain brews. How do you calculate extract efficiency?

Tony Bell
via e-mail

Mr. Wizard replies:

Professional brewers strive to brew the same wort day after day to achieve the most consistent beer possible. At least that’s the plan. One of the many things required to brew a consistent beer is knowledge about extract efficiency or extract yield. Malts change from lot to lot and brewhouse efficiency may change with time, so commercial brewers naturally want to account for these natural variations.

Almost every batch of malt produced in a commercial malt house is analyzed for the maximum amount of solids that can be extracted from the malt in a laboratory mash. The number produced from this analysis is called the laboratory yield. When brewers produce wort using the same batch of malt as a lab they almost always get less extract from the malt. This is because brewers use a coarser malt grind than the lab method and they collect less of the weak "last runnings" from the grain bed. The relationship between the brewery yield and the laboratory yield is a reflection of brewery efficiency and is referred to as brewhouse yield. To calculate brewhouse yield you only need to know three numbers: wort volume after boiling, wort gravity after boiling, and the laboratory yield.

This really is easy to calculate if you have a hydrometer and a way to measure wort volume. Suppose you produce five gallons of a 1.040 OG wort. If you multiply five gallons by 40 gravity points (the number following the decimal in the OG reading), you can determine the number of gallon-points in the wort. In this example there are 200 gallon-points. Although this is a strange unit, it works well.

Next, compare the gallon-points actually produced with the number theoretically possible. Suppose you used seven pounds of malt that had a laboratory yield of 36 gallon-points per pound. Theoretically you could produce 252 gallon-points of extract (7 x 36). Comparing the 200 gallon-points produced with the 252 gallon-points theoretically possible gives a brewhouse yield of 79 percent.

This calculation is easy on paper. However, calculating it at home is another story because very few malts purchased at homebrew supply stores state their theoretical yield. Even if the malt comes with a laboratory yield number, the number can’t always be trusted. Malts settle and small samples may not have the same properties as the whole batch, bags get mixed, old data sheets hang around longer than the malt bag they came with, and many malt suppliers give "typical" lab results to homebrew suppliers. Falling short of analyzing the malt yourself, you probably won’t know the laboratory yield of the malt you are using.

Most homebrewers (and many pub brewers) make educated guesses at the theoretical yield of different malts. This works reasonably well because the modern maltster is pretty good at being consistent; after all, we brewers demand it! Pale malt usually has a lab yield of about 78 percent, crystal is about 72 percent, rice is around 98 percent, and black malt is near 65 percent. Malt labs typically report yield as a percentage, and these numbers can be converted to gallon-points per pound by multiplying by 0.46.

The great thing about knowing your brewery efficiency and your malt yield is that they help you become consistent and are very helpful when trying to hit a target original gravity with grains you have never used. Those are really the only brewing issues related to efficiency unless you brew commercially.

If you make as much beer as Anheuser-Busch, the difference between 95 percent and 90 percent efficiency is about $15 million per year if the price of malt is only 15 cents per pound. For homebrewers making the legal limit of 200 gallons per year, the difference is a whopping $11.06 if our price of malt is a $1.50 per pound — not a big deal considering a couple rounds of good beer cost more than $11.06.

The other hobbyist aspect of efficiency is machismo. I mean, what good is 95 percent efficiency if you can’t brag? Kind of like the guy with the imported sports car that goes from zero to 60 in 4.9 seconds. All of his friends surely know his car’s prowess, but has he needed that acceleration lately, let alone used it?

Give me a system that is reliable, predictable and, most important, makes great beer!

Dear Mr. Wizard,

I buy bottled drinking water for brewing. The label indicates the water was purified by reverse osmosis and then "ozonated." Adding ozone disinfects, decolorizes, and deodorizes, but does the extra oxygen add any risks, especially since I’ve always read to "siphon quietly" to avoid oxygenation? Or is the term "ozonated" just a buzz word?

Jon Bakehouse
via e-mail

Mr. Wizard replies:

Water purified using reverse osmosis (RO) has been stripped of any chemical preservatives, such as chlorine and chloramines, that are added to municipal water. Thus, RO-purified water must be stabilized before it is sold. Although water exiting an RO purification usually harbors no microorganisms, the storage tanks and interconnecting pipework following the purification unit may. This is why bottled waters must be treated before packaging.

Two common methods used to kill microbes in water before packaging are ultraviolet light systems and ozonation. UV systems work by passing the water through a clear pipe that has a UV lamp shining on it. The UV light energy kills contaminants and imparts nothing to the water.

The other common method is ozonation. Ozonation works by bubbling ozone (O3) through the water. Ozone is a potent oxidizing agent and oxidizes anything and everything that it contacts. That’s why ozonation kills, decolorizes, and deodorizes — pretty nifty stuff! The only thing left in the water by the ozone is oxygen. However, any bottle of non-ozonated water allowed to sit around for a day or two after bottling will become saturated with oxygen from the atmosphere because plastic water bottles are oxygen permeable. This means that all bottled waters contain about the same oxygen concentration, roughly 10 parts per million, regardless of how they were treated before packaging.

Mr. Wizard, BYO's resident expert, is a leading authority in homebrewing whose identity, like the identity of all superheroes, must be kept confidential.