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This article on density meters assumes that you have a good understanding of proofing/gauging and the associated vocabulary. Check out our previous blog post “Proofing & Gauging 101” for that overview if you haven’t already.
A density meter is a device that determines the density of a liquid or gas, which you inject or pump into the measuring cell. The measuring cell is a small, U-shaped glass tube. The cell is mechanically driven to oscillate back and forth. The period of the oscillation varies with the density of the sample. Higher periods of oscillation correspond to denser liquids. Using a density meter, alcoholic proof (and % ABV) can be determined on spirits with a high degree of accuracy. Modern density meters can measure proof to TTB specifications in 1-3 minutes with as little as 2mL of sample. Compared to alternatives like hydrometers or pycnometers, the time savings are substantial. There are also major benefits to being able to proof with only a few mL of sample.
This article focuses on Benchtop Density Meters approved by TTB for use in place of Hydrometers & Thermometers. A list of those appears on TTB’s Website: https://www.ttb.gov/approvalalternatedevices
If you choose to purchase a non-approved density meter, such as the ever-popular handheld Snap series by Anton-Paar, you should know that you cannot legally use it for formal gauging. Such devices can be useful for quick measurements on the production floor, but you’ll still need a set of hydrometers and thermometers for compliant measurements.
There are three manufacturers that produce approved benchtop density meters:
| Manufacturer | Built In | Factory Warranty | Current Model |
| Anton-Paar | Graz, Austria | 1 yr, 3 yr if paying for annual PM | DMA 5001, 4501 |
| Mettler-Toledo | Switzerland | 1 yr | D6 |
| Rudolph Research | New Jersey, US | 3 yr | DDM2911+ |
Anton-Paar was first to market a digital density meter back in the 60s. They are well known in the market, and they price accordingly. Rudolph Research Analytical entered the market in the mid-2000s and has rapidly gained share, especially among distilleries. Mettler-Toledo, on the other hand, does not market as aggressively in the US.
All the meters on the approved list will work just fine for distilled spirits proprietors. The only downside is the cost – which is typically around $20,000-$30,000 for a new instrument. Financing is often available. Newer meters tend to be faster and require less frequent calibration. Older meters require more maintenance and time but can be found for $7,000-$10,000. If you are considering a used density meter, be aware that Anton-Paar and Mettler will not service discontinued models, while, in my experience, Rudolph will.
Unlike Hydrometers, density meters don’t have to be re-calibrated by a lab service; you simply test the density of distilled water and air in order to establish that the instrument is measuring correctly. There are meters from the 80s still in service, so you do have a good opportunity to amortize your cost over a long useful life. If you are considering replacing a suite of hydrometers with a used density meter, your break-even point might be only a few years away, given the relatively high cost of hydrometer recertification/replacement.
Both Anton-Paar and Rudolph Research Analytical offer additional instruments to enhance your density meter. Both firms have add-ons which allows you to measure the proof of obscured spirits (i.e. spirits to which sugar or other solids have been added). Rudolph Research offers a Refractometer for this purpose, while Anton-Paar sells a product called an Alcolyzer, which uses Near-Infrared for the same purpose. These add-ons are very useful but cannot legally replace the required bench-top lab distillation protocol for a formal gauge of obscured spirits. With that said, it is possible to petition the TTB to allow you to use a Refractometer or Alcolyzer for formal gauging of certain obscured spirits products under limited circumstances.
If you’d like guidance on choosing the right gauging instrumentation for your business needs and budget, reach out to me for a free 20-minute call with no further obligation. I have purchased and used both Anton-Paar and Rudolph instruments, used and new, and can advise you from my personal experience.
Tyler Derheim is Fx5’s in-house consultant, using his expertise to help distilleries of all sizes make it easier to make great things. Tyler first entered the regulated beverage industry in 2010, when he started working harvest and crush at a midsize winery in Slovenia. After returning to California in 2017 he joined a startup DSP, with responsibilities for formulation, production, compliance, lab services, and more. In 18 months, he led the DSP from mason jars and buckets to tankers and trailers, then moved into a freelance consulting role, helping distilleries of all sizes with every aspect of production, operations, and compliance. A long-time Fx5 user, Tyler brings a wealth of experience unmatched in the industry.
