REFERENCES: Lahne, J.; Abdi, H.; Collins, T.; Heymann, H. bourbon and Rye Whiskeys Are Legally Distinct but Are Not Discriminated by Sensory Descriptive Analysis. J Food Sci 2019, 84 (3), 629-639. DOI: 10.1111/1750-3841.14468. Barwich, A.-S. Smellosophy: What the Nose Tells the Mind; 2020. DOI: 10.4159/9780674245426. Barwich, A.-S.; Smith, B. From Molecules to Perception: Philosophical Investigations of Smell. Philosophy Compass 1903 2022, 17. DOI: 10.1111/ phc3.12883. Chambers, E. t.; Koppel, K. Associations of volatile compounds with sensory aroma and flavor: the complex nature of flavor. Molecules 2013, 18 (5), 4887-4905. DOI: 10.3390/molecules18054887. Lawless, H.; Heymann, H. Sensory Evaluation of Food Science Principles and Practices. 2nd Edition, Ithaca, New York. 2010. DOI:10.1007/978-1-44196488-5. Lawless, H. Quantitative Sensory Analysis: Psychophysics, Models and Intelligent Design. 2013. DOI: 10.1002/9781118684818. Meilgaard, M.C.; Civille, G.V.; Carr, B.T. Sensory Evaluation Techniques. 5th ed. Boca Raton: CRC Press/Taylor & Francis Group. 2016. DOI:10.1201/b19493. Meilgaard, M. C. Testing for Sensory Threshold of Added Substances. Journal of the American Society of Brewing Chemists 1991, 49 (3), 128-135. DOI: 10.1094/ ASBCJ-49-0128. Lee, K.; Paterson, A.; Piggott, J.; Richardson, G. Measurement of Thresholds for Reference Compounds for Sensory Profiling of Scotch Whisky. Journal of the Institute of Brewing 2000, 106. DOI: 10.1002/j.2050-0416.2000. tb00068.x. Barnes, Q.; Vial, J.; Thiébaut, D.; De Saint Jores, C.; Steyer, D.; Contamin, M.-A.; Papaiconomou, N.; Fernandez, X. Characterization of Flavor Compounds in Distilled Spirits: Developing a Versatile Analytical Method Suitable for Micro-Distilleries. Foods 2022, 11, 3358. DOI: 10.3390/foods11213358. Miller, G. Whisky Science: A Condensed Distillation; 2019. DOI: 10.1007/978-3-030-13732-8. Spedding, G.; Aiken, T. 18 Sensory analysis as a tool for beer quality assessment with an emphasis on its use for microbial control in the brewery. In Brewing Microbiology, Hill, A. E. Ed.; Woodhead Publishing, 2015; pp 375-404.
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ASCENDING METHOD OF LIMITS
PANEL FLAVOR THRESHOLD
Test Method
Example for DMS
A more involved method for flavor threshold determination involves a series of triangle sensory tests, see, for example, American Society of Brewing Chemists (ASBC) methods and the key references noted earlier for complete details (Lawless & Heymann, 2010; Lawless, 2013; Meilgaard, Civille & Carr, 2016 and Meilgaard, 1991). Such methods are based on the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO). This method also covers training on new compounds and gets the threshold value for an individual. Here is a considered example: six (6) triangle tests — each with two reference beers (lager with no addition) and one test beer (e.g., isoamyl acetate) are set up for presentation to a team. For a test beer sample, the concentration of the ester was increased each time by a factor of 2 in each subsequent triangle set; triangle tested in increasing concentration of spike (e.g., 1, 2, 4, 8, 16, and 32 mg/L). In each triangle set the question is asked: Which sample differed from the others?
With some repetition of the details from above, a simple example here will serve to illustrate the process and calculations. This example is from the spiking of beer samples with dimethyl sulfide (DMS). Some caveats to note: Most tests are run on beer/spirits where the concentration of the substance being tested is not actually known as it exists in the sample prior to the addition of the spiked test component. Thus, BET values are noted as concentrations (quantitative amounts) on top of that already present in the sample. Typically, a set of samples would be presented starting with a zero addition to the sample (a “control”), then Y ppm (or ppb) of the known/ test/training compound is added to the next glass, followed by successive doublings of the concentration (Example, 0, 12.5, 25, 50, 100, and 300 ppb) of the compound would be present in successive glasses. Such values are usually determined based on the known or estimated group BET as a central starting concentration. Here 50 ppb (anchor) is halved and halved again and doubled and doubled again. Noting here that the terminal value was set at 300 ppb, not 200 for this actual example — not a print error here. The assumption is that no one will selectively identify the component in the first non-zero (control) concentration sample glass (12.5 ppb) and certainly not in the control. Otherwise, the concentration that exists in the beer/spirit sample might need to be determined (as it is already at a detectable level, and that might reflect a naturally high presence in the base spirit). In that case, some thought on redesigning the experiment may be needed. Some people are eager to please — a natural bias — and want to “show off ” a bit. For very low threshold detectable compounds (those with high volatility that vaporize quickly) we have found that biases occur based on smelling the compound in the air from the higher concentration glasses (diacetyl a prime example). The volatile is released into the surrounding air and sensory booths or stations as others perform the assessment. So, we suggest that closed bottles be provided with instructions for a group to open each bottle at the same time and then in successive order and assess the sample (by pouring a small amount into an acceptable sensory evaluation glass or cup). Then all participants are instructed to close their current test sample bottle (pour back the remaining sample from glass to bottle or have the glass covered and set aside or perhaps removed by the panel leader before moving to the next sample). Panelist stations should be well separated if possible, and testing performed under suitable taste panel room/environment conditions,
Results The data are worked through similarly to that described above for the simpler method and although a bit more involved, simple programs can speed up the work. For example, in one study (see above) after training, the isoamyl acetate threshold in beer was shown to decrease (dropping from 7.8 to 3.9 ppm). This showed performance improvement for panelists as a whole and illuminated any need to recalibrate any individual palate. Distillers need to get up to speed with such methods and training, but be aware of the impact of high ethanol concentrations. Groups and organizations such as FlavorActiv, Aroxa (Cara Technologies), and the author of this article can assist here, but it is important to start looking at this type of training. An important note deals with the question of where to begin with the concentrations to use for such threshold testing. Threshold values are being increasingly reported upon in the literature and by suppliers of sensory stocks (FlavorActiv and Aroxa). See the article by Jeffrey & Spedding in Artisan Spirit issue 12 for some key values for starters. The American Society of Brewing Chemists member-accessible website has details of many component threshold values for beer, which also form a good base to launch from. A key starting point for whiskies is the early work of Lee et al., (2000). With an extensive list of many whiskey-related and other components provided by Miller (2019). A recent work by Barnes et al., (2022) is of current note.
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