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Why is my efficiency so low? Can someone explain my efficiency? I thought I understood efficiency. These statements are just some examples of the many threads relating to efficiency that I have seen on HomeBrewTalk. It would seem the forum is replete with individuals scratching their noodles in an effort to solve a conundrum their brewing data has presented. Fortunately, there are many helpful members who are ready, willing, and able to crunch the numbers, point out possible errors, and in many instances solve the riddle.
The purpose of this article is not to explore brewing-science's formulae and mathematics, but to illustrate some simple steps involved in the collection and interpretation of useful brewing data. Many homebrewers, myself included, use brewing software to crunch the numbers and calculate efficiencies. Through accurate data collection and analysis, brewers can more easily localize problems with their equipment or methods and find effective solutions. Lets look at two important numbers, mash efficiency and brewhouse efficiency, and explore what each of them means.
Mash Efficiency
This is a measure of how effective your methods are at extracting the starches from the grains, converting those starches to sugars, and getting the resultant sugars out of the mash-tun and into your boil-kettle. In other words, how effective you are at getting the available sugars into your kettle. Its no more complicated than that. To calculate mash efficiency we need to know three things.
  • The estimated maximum potential gravity points in the grain-bill.
  • The specific-gravity of the sweet-wort
  • The pre-boil volume of sweet-wort in the boil-kettle

How Much Sugar Do You Get From Your Grain
Maximum Potential Gravity
Every grain has a variety of descriptive numbers associated with it. One of these is its potential gravity and is measured in points per pound per gallon (PPG). This is the theoretical specific gravity of a gallon of wort containing 100% of the potential sugars in one pound of the grain. A grain-bills potential gravity is the sum of the gravity points available from each grain-type. Unless you perform your own grain analysis, this number is dependent on the accuracy of two things; the malsters grain data and weight of the grain-bill. Accurately weighing each grain-type is therefore very important.
Specific Gravity
A representative sample of the sweet-wort is taken from the kettle, cooled to the calibration temperature of the measuring device, and its specific-gravity measured. Hydrometers or refractometers can be used. I favor narrow-range hydrometers for their ease of use. Both the sample and hydrometer are cooled prior to taking a reading. If only the sample is cooled, adding a room-temperature hydrometer will induce a temperature change and small measurement error.

Potential Gravity Measured In Points Per Pound Per Gallon
The volume of sweet-wort prior to the boil can be measured in a variety of ways. A calibrated dowel, ruler or sight-glass are popular methods. Another approach is to etch volume-markings directly onto the kettle. This is the method I chose. Owing to the high temperatures (~170F) of the sweet-wort, pre-boil measurements must be corrected to account for volumetric shrinkage to the hydrometers calibration point. This correction, approximately a 2.5% reduction in volume from pre-boil temperatures is not automatically made by the popular brewing software I use.
Why is it important to measure mash efficiency?
Multiple enzyme mediated chemical reactions occur in a mash. These reactions produce the fermentable sugars and other compounds responsible for giving a beer its signature characteristics. Knowing how good a job we did at mashing (getting the sugars into our boil-kettle), can highlight procedural problems before and during the mash. Factors negatively impacting the efficacy and efficiency of a mash include:
  • Poorly crushed grain
  • An overly thick or gelatinous mash consistency
  • Excessively low or high mash temperatures
  • A large mash-tun dead-space
  • Ineffective sparging methods
  • Poor management of mash pH*
*Mash pH has greater impact on flavor but does effect efficiency, albeit to a much lesser extent.
After mashing and lautering, the wort is heated and boiling ensues with or without corrective measures. If mash efficiency is not in-line with the brewers objective, such corrections can include an addition of malt extract or an adjustment to the planned boil duration. This is a completely different, albeit related topic, beyond the scope of this article. When the boil is complete, the wort is cooled and transferred to the fermentor. Brewhouse efficiency can now be calculated.

Grain Crush, Mash Thickness And Temperature Contribute To Mash Efficiency
Brewhouse Efficiency
This is a measure of how effective your entire brewing process is. What portion of the total potential sugars made it into the fermentor. It can never be greater than your mash efficiency and is affected by volume losses during and after the mash. To calculate brewhouse efficiency we again, need to know three things.
  • The estimated maximum potential gravity points in the grain-bill.
  • The original-gravity of the wort (OG)
  • The volume of wort in the fermentor

Grain Potential, Wort Gravity And Fermentor Volume Are Used To Calculate Brewhouse Efficiency

Maximum Potential Gravity
This is the same measurement as previously calculated. It is based on the malsters data and accurate weighings of the various grain-types
Original Gravity
After the boil a representative sample of the wort is taken from the kettle or the fermentor. The sample is prepared in the same manner as before, allowing accurate measurement of the original gravity.
The volume of wort transferred to the fermentor is easily measured using calibrated markings on the fermentor. I ferment my beer in glass carboys and added etched volume-markings to them. Accurate markings eliminate any guesswork.

Really Get To Know Your Volumes
Why is it important to measure brewhouse efficiency?
Monitoring and maintaining a high brewhouse efficiency is extremely important for commercial breweries as it significantly impacts their overhead costs and bottom line. Efficiency related cost savings are minimal on the homebrewing scale. I would argue however, that there are important, non-cost related benefits to developing more efficient brewing practices.
Knowing how good a job was done at getting the sugars into our fermentor enables the brewer to more accurately formulate recipes and water volume requirements at each stage of the brewing process. Assuming mash efficiency is known, the value can also highlight volume losses after the mash and areas where ones methods could be improved. Factors negatively impacting brewhouse efficiency include:
  • Mash efficiency (brewhouse efficiency can never exceed this number)
  • Spilled wort
  • Dead-space in the kettle, chiller, and hoses
  • Wort absorbed by hops
  • Kettle-trub
With accurate data collection, and carefully directed refinement of the approach one takes to brewing, a greater understanding and control of its fundamental processes can be gleaned. Improved control of the home-brewery will inevitably lead to increased efficiency and a welcome additional byproduct; consistency. This is all-too-often overlooked when discussing efficiency numbers.

Take And Record Accurate Measurements
Unlike the astronauts in The Simpsons you dont need to be "a mathematician, a different kind of mathematician [or] a statistician", but you do need to take accurate measurements. Consistent and predictable efficiency better allows us to craft beers with intended characteristics, not ones dictated by inaccuracies inherent in our homebrewery. Isn't that a worthy goal?

Brewhouse Efficiency Calculations Aid In Brewing Consistency
The calculations involved in assessing brewing efficiency are not complex. Nonetheless, there are many beneficial reasons for using some form of brewing-software. There are lots of great options from which to choose. Many, like BrewersFriend.com are available for free.
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Wait....am I missing something? Why is the hydrometer photo indicating taking a reading at the top of the meniscus?? I always thought it was the bottom. Did I miss a memo somewhere??
@RunDadRun the photo appears to be done at the bottom of the meniscus.
Re the meniscus TOP not Base. (Read from the top* exceptions exist depending on the hydrometer)
This is only something I learned during the editing phase of this piece. Fortunately I was corrected by one of our more experienced and knowledgable members on HBT prior to publication.
Nope...it should be the bottom of the meniscus. The image on that wiki page link even shows why: the meniscus has the upward curve on both the side of the tube and the hydrometer due to capillary action. If you're reading at the top, you're including this capillary action. True reading is at the bottom of the meniscus, same for reading any sort of calibrated vessel (e.g., graduated cylinder).
If it reads anything other than 1.000 at the bottom of the meniscus when measuring distilled water at hydrometer's calibration temperature, then your hydrometer is off.
First, Excellent article and well researched. Second, When training new lab technicians (been a few years since I've done that!!!), I've always taught the API method, which is to read the instrument based on whether the meniscus is concave or convex. Convex, top of meniscus. Concave, bottom of meniscus.
As I said. I have always read (incorrectly as I've now learned) from the bottom of the meniscus exactly in the manner y'all are describing.
After having the issue explained to me (vis a vis the meniscus and fluid inside/outside a measuring device such as a burette or hydrometer) and reading a Quote from Ray Daniels' book, my error became apparent. I made the appropriate changes to the images in the piece. It is not surprising that this point is debated here as a quick internet search will largely "prove" me wrong. On this point however I will defer to Ray Daniels and work from the top of the meniscus from now on.
[The difference between top and bottom with the narrow-range hydrometers I show is ~0.001 and ~0.0005 with a finishing hdrometer. A hydrometer with a larger range will be subject to a greater potential for measurment error]
I would hope this likely point of confusion and contention doesn't detract too much from the article. Thanks all for reading and adding your feedback. It is very much appreciated.
Great write up Gavin! So many good points made here on how to calculate.
If people are looking to increase (or - gasp - decrease) their efficiency, there are lots of good stickies in the forum, including my own.
I'm not sure that volume adjustment need be done for actual preboil gravity readings. If the wort is consistent throughout, and you're cooling the sample, the sugar content will be appropriate no matter what, because they're all being read at the same temperature. It might affect your technical boiloff percentage, and can influence gravity points, but the difference is within the margin of error, and potentially overshot by things like insufficient mixing of preboil runnings, which can easily throw off a reading by more than 2.5%. Point is, I wouldn't bother with the correction.
Also, everything I have ever read except for Ray Daniels, including scientific texts, and the paperwork for my hydrometer, says to read at the BOTTOM of the meniscus. As hunter_la5 mentioned, it depends on your hydrometer. Some are indeed calibrated to read at the top. Most are calibrated to read at the bottom. Ray Daniels is wrong.
A few more points:
Re: Brewhouse Efficiency- Some things like loss to chiller are a known volume reduction and can be planned for all brews. Other things like hop loss are recipe dependent. You can calibrate brewhouse efficiency for the same beer over and over, or for similar "kinds" of beers from a trub/hop loss perspective (similar size/composition grain bills, similar weights of hops, etc), but the brewhouse efficiency between a Weizen and an Imperial IPA will be vastly different just because of hops alone, and this simply cannot be avoided. You have no choice but to anticipate it and plan for it.
Re: Mash efficiency- I think it's helpful to break that down into conversion efficiency and lautering efficiency. Mash pH, grain crush, water to grist ratio, mash temp/time, and such can have a big impact on conversion efficiency. Lautering efficiency is impacted by grain crush, but also by mash tun design. If you look to Kai Troester's work, you can get an idea of where your conversion efficiency falls, and then you can from there calculate your lautering efficiency. Can help you figure out exactly where your efficiency problems are.
The volume correction is needed as I measure the gravity of the preboil wort at 60F. I also need to measure the volume at the same temperature.
If it is not done the mash efficiency number is inflated. I was seeing this discrepancy between predicted and actual mash efficiency till i started making these required adjustments. Once I started making the correction the mysteriously missing sugars from reboil to post-boil vanished and my data was making more sense.
The hydrometer meniscus is something I was just informed about. After doing some more reading on the topic on the AHA website's forum it seems that it is entirely dependent on the hydrometer. I was not aware there was any debate as I had always read from the meniscus' base.
I did not breakdown the mash efficiency further as those numbers are not something most folks will measure. I was trying to keep the piece as approachable as possible. The factors affecting mash efficiency have their effects on either conversion or lautering and are listed together. Knowing the mash efficiency number is low is enough to prompt more thorough investigations by the brewer.
My lautering is rather simpler than what Kai undoubtedly covers. (I BIAB) My lautering is solely impacted by how much wort the grain absorbs. (Typically 0.045 gallons/pound)
I agree that some factors affecting BH efficiency are fixed and some are variable. Hops absorption as a variable can be easily calculated and factored in in the planning stage. What I have done is to allow for 1 quart of dead-space and trub loss in the kettle-chiller combo. Depending on the hop bill this more or less of this volume will be absorbed by the hops. Either way the amount remains largely unchanged at 0.25 gallons. If no hops were used it would be all wort/break material. With more hops its less wort. The planned BH efficiency remains unchanged. Probably if i did a massive DIPA or something I would need to rework the planned losses at a new fixed amount. Hope I'm making some semblance of sense.
Thanks for reading and providing such in-depth feedback. Much appreciated
Nice job Gavin!
Maybe you should use some sort of software that does adjust for thermal expansion at mash temperatures... :p
I reckon I know of a great online tool that does just that and more.:)
Very good point.
You're not going to plug it so I will.
@Gavin C I just read the 'talk:Hydrometer" link you posted, and I still have to disagree. That person is making the basis of their decision that it should be read at the top because their hydrometer appears to be miscalibrated. I just checked 4 hydrometers I own with distilled water, and 3 of them read 1.000 at the BOTTOM of the meniscus. The other is off by 2 points (and it was sold to me with that knowledge), and sure enough it reads 1.002 at the BOTTOM of the meniscus as well.
Occam's razor - which is more likely, that one guy (Ray Daniels) in one book was wrong, or every scientist in the world is wrong?
P.S. If you're calibrating your hydrometer with tap water, that will account for why you are getting 1.000 at the top of the meniscus instead of the bottom. There are trace salts in tap water that will cause your reading to be off by ~1 point. So your tap water is actually reading 1.001 at the bottom, which is indeed correct and thus you should be reading from the bottom for all samples.
Yea, I'm beginning to think I was too hasty in making the changes to the images prior to the article being published. When I did my calibrations (distilled at 60F) I read from the bottom at 1.000 for all 3 of my hydrometers that have a 1.000.
I assumed I had made a trifecta of errors. It was too late in the day so I just made the changes anyway. I will need to recheck my devices. Like I said, I have always read from the menisus' base. The image is at odds with my past practices. thanks for reading .
Great article, thank you for the work you put in!
As far as the meniscus, in college I was taught to read at the bottom. However, I believe that being CONSISTENT is the key. Those that prefer to read from the top, keep at it and don't change! Those that prefer to read from the bottom, keep at it and don't change! In the end it will be beer.
I believe that the scientific community has "rules" or "best practices" for taking measurements for consistency, not because it is the ONLY or RIGHT way. It just creates repeatable consistency!