measurements of the extract content of their grains and mash, and can then predict the alcohol yield for each batch fermentation. The same can be said for sugar-based spirits manufacturers. Their predictions will be monitored by a follow-up alcohol analysis often by High Performance Liquid Chromatography (HPLC) (see Heist, 2015). This process will form the topic for a future issue, but illustrates the first point in the distilling process at which alcohol is often measured — following fermentation. The distiller can then make predictions on spirit yields from distillation itself. Alcohol content needs to be determined following distillation to ready for cask filling, after maturation (perhaps even at several time points during maturation), and at bottle filling. Bottles (or cans) may be tested for alcohol content for regulatory compliance and tax purposes. Distillers must learn to measure alcohol at the very least. Today, with highly sweetened spirits, they also need to be able to measure the residual extract or real extract (the extract representing the sugar, protein and mineral content in the absence of alcohol) (detailed and defined further below — see Apparent and Real Extract — An interlude). This value can then be used to help determine total product calories and other nutritional data (also detailed below). If fats are present this represents a more complex topic and it is recommended that the distiller making spirit products with fats present (cream or egg-based liqueurs for example) consult with a food or alcohol beverage testing lab familiar with assessing such products for reporting complete nutritional profiles (and see www.ttb.gov/ssd/documents/ssdtm407carbshsld.pdf); there are noted issues with this documented method — in particular this author has reservations about the solids determination methods outlined by the TTB in this directive — the reasoning is complex and not discussed here but see Spedding (2016) for details and a final note at the end of this present paper). One highly noteworthy point here is that the TTB agency draws upon many samples from the trade each year. Their published reports always reveal a significant percentage of erroneously listed alcohol values on spirit labels. Clearly distillers are either not correctly determining the alcohol content of such spirits, or their third-party test facilities are not doing their job properly. Getting this right is thus of the utmost importance! A comprehensive review on how to determine alcohol content and extract values has appeared recently (Spedding, 2016); and, even though the reference mainly deals with beer, it shows the use of proper tools, methods, and robust algorithms needed to obtain accurate data. Currently user error, both through incorrect instrument use and method performance, is the main cause for many calculation discrepancies. A final important note on alcohol values for nutritional (calorie) determinations. The alcohol by volume is converted to a weight basis by use of conversion factors based on the specific gravity of alcohol and the actual spirit specific gravity. Many brewers and distillers get this value wrong if using hydrometers and or refractometers or simpler density meters. And more importantly here is that many testing laboratories also either miss this point and/or get this wrong! Amounts are expressed in grams (see Spedding, 2016 for a full discussion on alcohol determination methods and respective WWW.ARTISANSPIRITMAG.COM
calculations). The % alcohol by weight values (ABWt) will also be utilized below in example calorie calculations. A quick note on this to show the conversion for an accurately determined ABV to ABWt is shown here:
ABWt = ABV x SG alcohol SG sample
[Eq. 1]
Alcohol by weight (ABWt) and by volume (ABV) are expressed as % by weight (w/w) or by % by volume (v/v) respectively. The specific gravity (SG, or “relative density”) of pure alcohol is taken as 0.7907 (for 20°C) and the SG of the sample is the actual determined value obtained via density meter (either with or without prior distillation depending upon solids or extract content). Alternative methods for alcohol content determination when extracts are in high concentration are not further considered here (see references cited earlier in this section).
APPARENT AND REAL EXTRACT
An interlude
see Artisan Spirit online for more definitions: artisanspiritmag.com/definitions-01/ So, what do we really mean when discussing extract values? Brewers measure changes in density as sugars (the original extract being mainly carbohydrate in nature) are consumed during fermentation and converted into alcohol. This causes a drop in the density and the extract value. Measurements are obscured (the true gravity is “hidden”) by alcohol (of lower density than water, sugar solutions or beer) causing “buoyancy effects” with hydrometers, for example. Thus, false or apparent readings of gravity are made when instruments measure beer (containing water, sugars and alcohol); hence “apparent extract.” For distillers, the same principles are in effect, but the extract is from the addition of sugars, proteins, and other solid materials from flavor additions, such as fruit. So, in cases of high solids content, the distiller needs to run laboratory scale distillations to separate the alcohol from the extract (solids) and to determine the alcohol SG in the distillate (largely the alcohol and water). The solids are left behind in the “distillation residuals” but can be determined by bringing the distillation pot contents back up to the initial sample volume and measuring the density of the extract-containing solution (with no alcohol present) to obtain the extract content; tables and algorithms being used for the distiller to be able to convert the density into the Plato extract values. The real extract is a true(r) measure of remaining sugars — and proteins etc. — as determined in the absence of alcohol (removed via distillation or boiling). When distillers measure a sample containing sugars this will be an “apparent” gravity and neither the true alcohol content or extract content can be directly determined. The true or real extract is ultimately expressed in grams per 100 grams of sample (a Plato value) and is needed to obtain, along with the alcohol by weight value, the correct caloric content of a spirit sample. Moving on we now consider calories and other nutritional values.
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