Specific Gravity and You

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After my last “high flying” post on why American whiskey is so problematic, I thought I’d bring things back to earth and teach some foundational concepts. This lesson was part of my consultancy, but my time is a little pressed so I’m not exactly out marketing it anymore. What is specific gravity and how far can we stretch measuring techniques to harness it?

I’ve long preached to distilleries that they should make a bunch of very small scale secondary products. Most all these business school types turned distillers think it is a terrible idea. It will dilute their core product, not strengthen it like I propose. It will confuse their sales efforts. It will confuse their investors. What no one seems to admit is that they have near no clue what the hell they are doing on a technical level and they need to practice on stuff. They also need to enrich their retail businesses plus benefit from new products having PR synergies with their core products (this last point is more powerful than anyone realizes). Many operations also need new retail scale products to help them retain top talent. I do not work in a distillery because no one has figured out how to properly pay me.

Before we get into it, a whole category of products simply does not exist (in practice) because firstly there are no dreams and secondly most new distillers have not figured out how to accurately vat complex multi component blends. I’ve seen distillers so frustrated by proofing that they bought bench top Anton Paar densitometers for startling money while their labs had near no other analysis equipment. Most new liqueurs are nothing but mono, no doubt both because of a lack of dreams and technique. Our understanding of vatting has not advanced an inch despite 10,000 bitters producers working in the territory. What’s up with that?

Specific gravity is the density of a substance compared to another which in most all cases is luckily just water. It doesn’t have to be water, but another reference might only be used in petro chemical industries and may be a yesteryear concept now that analysis procedures are different.

Specific gravity is basically density (independent from either metric or imperial measuring systems) which is mass/volume. g/L

If you know the density, the mass can tell you the volume and vice versa. Distilleries typically use this with quite large scales, weighing entire barrels to gauge them. This also becomes conversely very useful on the small scale or anywhere in between when the containers become tricky. There are techniques to measure the density of mere drops of essential oils (there is a technique for a mere drop that requires a special type of microscopy slide as a pycnometer).


A hydrometer is the distiller’s go to specific gravity tool, but it is often the least appropriate option. Cheap, fast and good, pick two. Hydrometers are cheap and you can own a ton for a fraction of the price of great scales. You can stick one in a fermenter and get a quick reading without making a mess of glassware. You can stick a hydrometer in a still parrot and get inline continuous measurements that can become actionable such as starting or stopping a run. Hydrometers typically, however, will never give a lot of significant digits.

Refractometers are a tool we should quickly get out of the way. They convert refractive index measures to either density or related measures. They are not exactly cheap, but they are fast and can work in challenging circumstances. They can also take a single drop and give you actionable advice such as when to harvest a crop. They do not provide many significant digits. I have low and high brix scale refractometers, but I use them far less than I used to. You cannot use brix refractometers on alcoholic solutions because the results get very significantly biased.

The fine coffee scene has been loving digital refractometers lately, but it may not be their best option. Or actually it may, because of how companies like VST have made the advice so actionable (they even have an app!) Refractometers for coffee require filtration because particles obscure and haze the reading. Coffee is typically sucked through a syringe filter before it is put on the refractometer. Another method very useful to the distiller may actually serve the coffee scene well, but so far it is not widely explored and we’ll get to that (I actually have a rare 1970’s text called The Coffee Hydrometer that I’ve been meaning to digitize).

The most accurate tool a distiller can use probably isn’t legal with the gaugers and that is why it is not practiced for tax work like proofing. The revenuers have long endorsed certified hydrometers and certified thermometers, but they are not exactly the most accurate.

The most accurate way to measure density may be with the specific gravity bottle (pycnometer) and a very good scale (and thermometer!) which is what many spirits researchers used in the old school. The bottles come in various sizes and are designed to hold very precise round number measurements (at 20°C). The bottle is filled to its neck and a special stopper forces excess liquid up a tube so at the top of a narrow aperture it hits 1.000 liters or some such number with confidence. Cheaper brands I’ve bought were never accurate (or my temp was wack?), but you can still calibrate them yourself, though next time I’m going to spend money for quality. When your volume measure has significant digits your density measure is only limited by the quality of your scale. My favorite scale vendor is Old Will Knott. I’m glossing over temperature, but modern sous-vide immersion circulators make it much easier to control for. If you need all the significant digits, a liquid can be held at constant temp before it is put in the pycnometer and weighed. Be aware, for each percentage point of alcohol, the change in specific gravity is roughly 0.0016 so you will need a scale (at that point what is called an analytic balance) which has that many significant digits.

I have done a ton with scales. Remember, I developed the idea that you can weigh carbonation for sparkling beverage production with a kitchen scale.

We can walk all those pycnometer concepts down into practicality. An outstanding distillery tool is the 5 mL automatic pipettor (5000µl). They are about $70 and can be paired with a $100 jewelers scale to get many significant digits. Their repeatability is excellent and can be tested. A portion of liquid can be put on a scale and the pipette tip primed then liquid zeroed (youtube is full of technique videos). A 5 mL amount can be removed twice to prove repeatability and get the measurement into base ten (10 mL) so density is easy to calculate.

Density should be recorded constantly in competitor analysis scenarios. Basically everything that comes through the shop. With the printed alcohol content, sugar content of liqueurs can be extrapolated or the slighter measure of obscuration investigated. This is important for vintage spirits where you want to get an idea of either sugar content or obscuration, but you don’t want to destroy a large sample. With a density measure and then a 5 mL sacrifice to dehydration lots of vintage spirits can be investigated for alcohol content in their current state and obscuration in their pre-ullage original state (Weigh the bottle before you open, weigh it again after you drink and empty it. Coupled with the specific gravity, you’ll know its volume in its present state and not mess with your good drinking. Never put that stuff in a graduated cylinder). So much vintage booze is being consumed where we would all benefit from rudimentary 5 mL sacrifice analysis projects.

The pipettor process will likely work for coffee quite well with no filtration. The 5mL pipettor can also be used to fill tasting room glasses for nosing and gratis samples. The pipettor with its digital scale can also be used to rapidly assemble different generation of vatted products in 100 mL or less batches. Precision at 100 mL means you can quickly assemble ten prospective generations of a recipe for assessment progressing a single variable at a time. You are left with no reason to not see ideas fully elaborated. I also create sketches, but more on that some other time.

The most profitable idea I’ll share is the rule of 1.587 which is the density of sucrose (or 1.59 if you don’t need that many significant digits). The density of sucrose can reveal how much volume a mass of it takes up and thus reveal other measures we need to hit certain targets.

If we are making an Amaro that we know we want to have 280 g/L of sugar and 24% alcohol, what do the parts look like? What volume will the sugar take up? 280 / 1.587 = 176.43 mL. So the sugar free rest of it has a volume of 823.57 mL. Now how much alcohol does that start with if it is going to be diluted by sugar to 24.00% on the revenuers nose.
(823.57 * X) + (176.43 * 0) = 1000 * 24.00.
(823.57 * X) = 24,000
X = 29.14

That 823.57 mL is going to be a vatted collection of individual concentrated components. As they take shape, they can be shifted, subdivided, even combined. Certain components may bring a sugar content that needs to be deducted from the 280 such as a fruit juice. Pretty soon you’ll have a spread sheet.

Some components may exist in such small quantities that a hydrometer just isn’t going to work, but you still should know the specific gravity of everything so the SG bottle or pipettor must be used.

Now you have to scale it up. Sometimes this is to roughly five gallons (tasting room) and maybe to 500 or so gallons (wholesale). You should have a plan for the order of operations in which you combine components that harnesses all your available scales to quickly get you to a target with confidence. Proprietary narrow range hydrometers could be used to quickly check your work (and check off sheets made in case the phone rings and you walk away, but SG knows all). Eventually a final check has to be made and a plan for correction. The final point of concern is percent alcohol to satisfy the revenuer so either water has to be added or concentrated ethanol. The added sugar should be very easy to hit accurately so the error is most likely with the alcoholic quotients. Any addition to average up or down the alcohol content will have to preserve the sugar content so sugar might need to be added to your bump.

These operations should be practiced at different scales and employees should be given sample puzzles to solve before they risk expensive ingredients. This is basically the premise of my distillers workbook exercises.

Elaborating a vatting procedure can keep you safely away from all in the pot cooking and push you firmly into the progressive process. Fragmentation of the product is literacy in the product. Ideas can move towards deeper involvement.

The amaro challenge can push beyond mere assembly for a distiller and into wielding special effects to create sensory differentials and tone refinement to push expressions from ordinary to extraordinary. Every distillery should have an Amaro and it should be a measure of their relationship with beauty and capacity for abstraction.

None of this is too complicated, but none was spelled out in educational books for distillers. Modern texts only teach the maintenance and continuation of large scale products, not the origination of small scale products. I have used this all to develop two notable products on the market that have done more than $300k per year in wholesale revenue. One is more than ten components while the other is merely three, but extrapolated all the way from a single cocktail to a nearly 250 gallon batch. I’ve developed countless others that exist only as one-offs or as proof of concepts in the event extraordinary source materials become available.

Good luck!

As far as data tables goes, for the specific gravity of sugar solutions, the data table I’ve used the most is C440. For ethanol solutions, it comes from a text because most do not have the full range at the lower ethanol contents which becomes important to certain types of work. Your vatted projects may never require charts, but you will definitely need them for competitor and role model analysis when you want to become hip to the common structures liqueurs and amaros take. If you use a great resource, please share it up.

4 thoughts on “Specific Gravity and You

  1. Anyone who gives a damn should certainly have pipettes and the knowledge and observation skills to use/maintain them. We use 200uL, 1000uL, 5mL pipettes to exact recipes after quickly roughing in ratios with a disposable 5mL squeeze pipette. Very precise blends (by most standards) are made on the 10-20mL scale using a slick spreadsheet that lets us manipulate components without losing track of what’s going on. It all gets scaled in the end with consideration for the nuances of our particular set of equipment.

    I am curious if you have a specific sugar you use for your sweetener? I ask because it’s interesting that the density of pure sucrose works for volume effects. With a lot of solutions there is some funny business that happens as molecules reorganize during mixing. For example, if you were to utterly enthrall yourself by calculating the volume of all the actual molecules within a cubic cm crystal of sucrose, you would find that volume to be significantly smaller than the cubic centimeter crystal. The space between individual molecules in the crystal lattice represent this difference, and it’s there that water or other solvent are often quite happy to reside. This can *potentially* to throw volumes off in one way or another, similar to what we see with ethanol and water solutions. That said, standard mL/g contributions are very helpful here for sugar, honey, maple, etc, in our batching process. I prefer to just find “density” values empirically though in order to avoid unexpected deviations, like moisture content. We find stock solutions work best to rough in an ingredients’ contribution while also allowing for quick and precise additions during development stages. In the end, I generally just scale the milliscale recipe with simple math, distill it to find true proof, then make the requisite adjustments to hit the target profile and bottling proof. Distilling to determine proof is inconvenient but there’s really no way around it with a lot of liquids, so we try to just let it work in our favor.

    I would also advocate for secondary products at a facility with the proper resources. They are a lot of fun and are great opportunities to think well outside the box. Some of ours are very targeted while others serve to fulfill the potential of our plant’s capacity. There was a point where we threw a lot of “waste” in the compost but not anymore. I’ll reiterate that it can be a bit of work to make ideas happen, but you’re absolutely correct that they enrich the tasting room experience. We also find it expands the market to those who are reluctant to even taste “liquor”.

  2. Thanks for supporting and validating the ideas. I’m aware of the contraction and hope eventually to find some rules of thumb for estimating it that can be shared. The point is that many have avoided such products because they couldn’t handle or reinvent the broader concept. We should be sharing these ideas with each other because the confidence that we build in new distillery products (as opposed to mass market) raises all ships.

    I have really hit brick walls talking about secondary products and even byproducts with prospective employers. How do you create an extraordinary well evolved gin? well you just may need a well selling sloe gin to pull it off.

    cheers! -Stephen

  3. Sloe gin because of the flavor layers beyond aromatic? Byproducts aside, those kinds of variations always seemed one of the great things about the gin category as a whole. There really is a ton of flavor-space out there that falls under gin’s classification and perceptual umbrella but hasn’t been fully realized in one way or another. No reason gin can’t have as much evolutionary potential as an IPA or the nuance of an aged rum or whiskey. Finessed extractions & distillations, botanical terroir, water chemistry, fractional aging & blending, bioflavoring, and even post-distillation additions of stuff like fruit or ultra-low volatility elements. They’re all great ways to evolve the class and sculpt a new liquid moonscape.

  4. The next step with gin, I think, is botanical charge standardization. I have a great set of lab protocols for it. I thought what I have was completely unknown, but someone I correspond with from Sacremento knew where I got them when I hinted. He is however, unusually smart.

    I think it is dangerous to encourage people to branch out until protocols for consistency become well known and easy to apply. A lot of ideas should start at the tasting room scale and grow. The market is so flooded as it is. Sadly there is no one employed at the tasting room scale that can execute anything.

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