All About Efficiency

When brewers speak of efficiency, what do they mean? Basically it means the percentage of sugar you extract from your grains during your mash and/or lauter. Breweries need to get as much sugar out as possible because this will affect their overall cost of goods and their bottom line. Plus it allows them to have a consistent product. Home brewers need to know their efficiency so they know how much grain to use to hit their target original gravity and for consistency. Plus there are bragging rights when you have a high efficiency. If you are brewing on your system for the first time you won't know your efficiency. Most people assume 70% to start off. There are different points in the mashing/brewing process that you can test for your efficiency, after conversion, in the kettle and in the fermenter. But first you must know about points per pound per gallon. Points per pound per gallon (ppg) tells us the yield of sugars that you extract from your grains. In the case of malt extracts it tells us how much sugar there is per pound of extract. Simply put, one pound of grain that has had 100% of it's sugars extracted (yield) will give you a certain gravity in one gallon of water. For example, if a pound of a grain has a 100% yield of 37 ppg, you would end up with a gravity of 1.037 in one gallon of water. (We drop the numbers before the decimal point when talking about ppg). But this is only if you are able to extract 100% of the grain's sugars, which no one can really do. The yield of a grain is based on a scientific mashing method called a Congress Mash. Most malt sheets will give you both an extract fine grind dry basis (fgdb) or an extract course grind dry basis (cgdb) which is the percent of sugar that is available after the congress mash. I like to go by cgdb because most mills grind fairly coarse. I said percentage because there is usually about 20% of the grain that does not convert to sugar in the mash, i.e. hull and proteins. The percentage to ppg is based on sucrose having a ppg of 46. So if your cgdb is 78% of 46 then your 100% yield is 36 ppg. Most base malts like two row have a ppg of around 36. If you are not into math don't fret, there are plenty of charts that will tell you the ppg of every grain, usually they will call it yield. For malt extracts, most dry malt extracts (DME) have a ppg of 45 and most liquid malt extracts (LME) have a ppg of 35 (lower ppg since they are around 20% water). This is very helpful to the extract brewer who wants to figure out their original gravity. Every pound of DME added to a five gallon batch will raise the gravity 9 points, or 1.009, every pound of LME will raise the five gallon batch 7 points. Knowing the ppg of the grains you are using is the only way to know the efficiency of your system. Knowing the percentage of sugar you are able to extract will allow you to calculate the amount of grain needed to hit your OG (Original Gravity). But there are different times in brewing that have different efficiency calculations. The first point you can test is called the conversion efficiency. This will determine if you have converted all of your starch to sugar in your mash. Sometimes people will use an iodine test to see if the starch converted to sugar, a drop of iodine in a sample of wort will turn black if starch is present. This does not tell you if all of your starch has converted to sugar though. It just tells you that the starch that the saccharification enzymes got to have converted. There can be starches still left in the hull from a bad crush that did not get hydrolyzed. You want 100% conversion efficiency or close. I know I said no one usually gets 100% efficiency but that is after the lauter/sparge, I will get to that. For conversion efficiency you want all your starch converted to sugar before the lauter/sparge. The math is simple. Take a gravity reading of your mash after you are finished mashing, before lauter/sparge. Adjust for temperature, (a refractometer as opposed to a hydrometer helps with this. Uses a lot less wort and adjusts for temperature almost right away). Add the ppg of all your grains according to weight and divide by your mash water volume in gallons. This is the ppg (yield) of your grains combined at 100%. Then divide your measured mash gravity by the ppg of your grains and that is your conversion efficiency. Hopefully your grain ppg and your mash gravity are very close. If not, you know you have conversion problems and this can be due to temperature, water to grist ratio and ph among other things. Those are topics for a different time. For example, lets say your grain bill for your 5 gallon batch is 10 lbs of 2 row malt at 36 ppg and 2 pounds of caramel malt 20L at 34 ppg. Your overall grain ppg is 428 points. Divide this by your mash water at 1.3 qts per pound which is 3.9 gallons. You will have 109.74. This is your 100% ppg extract yield. Divide this number by your mash gravity reading, this is your conversion efficiency. Anywhere in the high 90's is close enough for rock and roll. I rarely take a conversion efficiency reading unless I am having a big problem with my kettle efficiency. The pre and post boil gravity numbers are what most people are looking at. Conversion of the well modified malts we have now days is easy. I swear sometimes if I look at those grains long enough they will turn to sugar. What we really care about is the amount of sugar that gets into the kettle. This is usually measured pre-boil, after the lauter/sparge. This is a combination of conversion efficiency and the amount of sugar we rinse during our lauter/sparge. The type of sparge we do after mashing is very important to our kettle efficiency. Batch sparging, where we lauter off our first runnings completely and then add more hot water to the mash, letting it sit to dissolve the sugars and then lautering again is the easiest way, but the least efficient. Continuous, or fly sparging where we continuously add our sparge water to the mash while we lauter until we get our pre-boil volume is the most efficient, because sugar that is suspended in water will stay suspended, making for a better yield. Figuring out our kettle efficiency lets us know how efficient our overall mash process was and allows us to adjust our recipe accordingly. The math is similar to the conversion efficiency math. First we take a temperature adjusted gravity reading of our wort at pre boil volume. Be sure to mix your wort gently before taking this reading because sugar tends to stratify during the lauter/sparge. We still want to know the total ppg of our grain bill. We then divide that number by our pre-boil volume in gallons. That is your grain bill 100% ppg yield in the kettle. Then divide your pre-boil gravity points by your grain bill ppg and this will be your pre boil kettle efficiency. Using our grain bill example from above, we still have 428 ppg of the grain. Divide this by our pre boil volume, let's say 6.5 gallons for a typical 5 gallon batch. This gives us a ppg of 65.84. But the gravity reading you took was 1.052 or 52 points. Divide 52 by 65.84 and you end up with an pre boil kettle efficiency of 79% which is pretty darn good. Your post boil OG will be higher because you are boiling off water during the boil and concentrating the sugars, but the efficiency will remain the same. To figure out your post boil gravity from your pre boil gravity, times you pre boil gravity points by your pre boil volume and divide by your post boil volume. In our example, 52 x 6.5 = 338 / 5 = 67.6 or an original gravity (post boil) of 1.067. Here is a calculator to make this easier. There is one more efficiency reading you can do and this is called the fermenter efficiency. This is the efficiency after the wort is cooled and transferred to the fermenter. There are points lost due to hop absorption, kettle loss and loss to hot break. If you really want to hone in the efficiency of your system you will write your recipes using this number. The math is the same as the kettle efficiency only this time you take the gravity reading of your final amount in the fermenter, use the volume that is in the fermenter and still use the same grain bill ppg. When writing a recipe you do all this kind of in reverse. I usually write for five gallons. I would add up my grain ppg, divide it by 5 (gallons) then times that by my efficiency percentage. In our example, 428 / 5 = 85.6 x .79 = 67.6. Knowing my efficiency allows me to adjust my grain bill to reach my gravity points. Thank goodness we have online calculators to do all this for us! Efficiently yours, John
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