My first article on this topic was titled “80 Years of Rapid Maturation Studies – Why Are We Not There Yet?”[1] We are now just five years distant from the publication of the first part, so why, then, did the date in the title change by over a half century, from 80 to 136 years?
A visit to the last Worldwide Distilled Spirits Conference in Edinburgh (May 2023) led to a meeting with Scottish whisky expert Alan Wolstenholme, who reminded me about a very neat book originally published in 1887 entitled The Whisky Distilleries of the United Kingdom, by Alfred Barnard.[2] Mention was made therein of “rapid maturation machines” (more on this later). In addition, that colleague pointed me to another work: The Manufacture of Whisky and Plain Spirit, by J.A. Nettleton. According to the Scotch Whisky Auctions website, Nettleton’s book, first published in 1913, is regarded as one of the rarest and most important books on distilling.[3] In 2009, it was painstakingly reprinted in a facsimile edition of just three hundred copies (Classic Expressions, Pitlochry, 2009.) Thanks to another colleague I now have a copy of that original print edition volume. That volume also cursorily discusses rapid maturation (from 110 years ago) and some “tweaks” to maturation processes or conditioning of warehouses to effect a quicker release of product to trade. Some mention will be made as to those processes, which preceded those noted from 80 years ago, which were based on U.S. research and publications.
This first section of this revamped preamble briefly introduces earlier published notes on “rapid-maturation methods” and other papers and patent details not covered in the edition from five years ago and briefly reviews material from those first stories. The reader is encouraged to seek out the earlier publications — available online at the ADI website or via e-book — so that repetition could be avoided here. In the months to come, look for another installment in this series presenting the newest research, ideas, and concepts applicable to an understanding of the maturation of brown spirits in wood, be it in traditional barrels or by the addition of chips, staves, etc., as is sometimes done in modern craft distilling practice.
Barnard and Nettleton Tell Their Stories (With some interjections regarding modern research notes)
Barnard: The Yoker Distillery near Glasgow is covered by Barnhard, and a walk-through discussion of the distillery leads to an interesting though cursory statement: “It is a smaller building than the others, and contains a Patent ‘Ageing Apparatus,’ where new Whisky is subjected to an immense pressure of heat. This process is said to have the power of destroying the aldehyde or fieriness of new Whiskey and converting it into a mature spirit of three to five years old. This patent is at present in its infancy, but arrangements are being made to work it in this Distillery on a larger scale,” writes Barnard.
Exactly what an “immense pressure of heat” means eludes us, though heating up any chemical reaction usually affects an increase in the rate of product formation (forward or reverse direction, equilibrium, or fully reversible processes). The physicochemical/thermodynamic principles may be found in textbooks and with neat short outlines (dealing with the important Le Chatelier’s principle).[4] Additionally, Lost Spirits filed a modern-day patent dealing with light and heat processes.[5] Distillery Trail described the patents filed by Lost Spirits for rum maturation in 2017.[6]
The Lost Spirits patent authors describe processes for maturing distilled spirits that involve heat-driven esterification reactions and photocatalytic polymer degradation of oak barrel staves. Such chemical processes need to be better understood and related to sensory profiling as discussed in the original “80 Years of Rapid Maturation,” and which will also be covered in Part 2 of this revisit to the topic. Key principles and bringing big data analysis — under the umbrella of so-called OMICS technologies as related to the maturome or spiritomics — will give us further insight into this complex topic, and some details on these approaches are covered elsewhere by the author[7] (4) and are treated in Figures 2 and 3. The maturome is the coinage for the complex spirit-in-wood barrel engine maturation process, and spiritomics represents the concept for the complete process from raw materials through process to final matured and bottled spirit. The oak wine barrel as an active vessel was also proposed by del Alamo-Sanza and Nevares.[8]
Nettleton. Nettleton’s book covers several notes and sections on artificially maturing spirits. “Vignier’s patent,” noted by Nettleton, refers to the maturation of spirits in vats by passing alternate currents of hot and cold air, or hot and cold oxygen or ozone, through the spirits. As we understand it today, a “controlled uptake” of oxygen (micro-oxygenation) leading to micro-oxidation is considered necessary and sufficient to promote controlled reaction chemistry and not lead to over-oxidation of beer or spirits, which could lead to old/stale flavor notes. Thus “Vignier’s” method seems to be a little excessive or uncontrolled, at least as far as the details provided by Nettleton seem to describe. Much more work has been done with wine in barrels (and bottles) and oxidation processes to date than for spirits. However, a few cogent articles worthy of review, and to be covered in greater detail in Part 2, have seen recent publication.[9] [10]
Nettleton further states: “More successful methods of imitating maturation are those which aim at exaggerating or multiplying those slow natural influences which are known to effect the same result in the course of time.” Such tenets were covered in a patent by Mills and Barr, No. 18,212, 1890 (cited in Nettleton but no longer readily discoverable, it seems). However, new whisky was subjected to the passage, through the liquid, of alternate currents of cold and slightly warmed air.[11] Before and after such aeration blasts, some sherry or other wine was added to the spirit along with small amounts of either sulfuric acid or potassic hydric sulfate (potassium hydrogen sulfate or potassium bisulfate), the latter supposedly to intensify the action of the wine. The mineral acid and/or potassium salt were subsequently removed via neutralization and precipitation, and “the whisky is eventually removed from the small sediment which occurs.”
Why such additions, then removals? Are the details still out there in old archives (or recoverable patent files)? Or lost to the Scottish mists of time? Other patents with some variations on the above processes and conditions and involving the use of wine leading to alterations in maturation are mentioned and detailed by Nettleton: “Such a process undoubtedly improves the casks and imports a softness to the spirit, but it in no way solves the difficult problem of maturation.” What the nebulous, hedonic term softness meant is of course lost to us.
We should note, though, that in winemaking excessive potassium levels are associated with high juice pH and possibly “wine development” (a somewhat nebulous topic, but widely discussed in the literature[12] and often referring to the “brightness” of wine). During winemaking, a high concentration of potassium causes precipitation of free acids (mainly tartaric acid) leading to an increased wine pH. This high pH may reduce the color stability of red wines and may also reduce respiration and the rate of degradation of malic acid.
It is known, for example, that the acidity level in the barrel needs to attain a certain level before any other spirits maturation chemistry can occur[13] and, as pH is important in many reaction processes (pH dependency), could that be why potassium salts were used in the process for patent No. 18,212? Or was the value of acid addition merely for sulfate addition, or again, for pH changes? The rise in acidity required for subsequent spirit maturation reactions to occur is described in the original installments in this series. However, it raises the question: Did the wine add something else to the process, and could this assist maturation of spirits matured in previously wine-filled barrels? Furthermore, micro-oxygenation and oxidation reactions and ion-dependent or stimulated reactions may also be important here (activities of wine phenolics or flavonoids, etc.). Time for some new experiments with new state-of-the-art monitoring devices and analytical instruments?
Hints about the relationships among acids, esters, color, and solids in “a properly aged whiskey” were first noted by Crampton and Tolman in 1908, whereby they concluded that such relationships “will differentiate it from artificial mixtures and from young spirit.” How such relationships work with spirits in barrels or alternate vessel systems must be understood too. A patent assigned status in 2003 (Brown-Forman[14]) covers solvent extraction and additions of extract to ethanol to generate a “beverage having the taste of a mature oak aged alcoholic beverage.”
Another patent process described in “80 Years of Rapid Maturation” dealt with the addition of ethyl acetate to maturing spirit and was said to promote a rapid maturation of that product.[15] However, due to subsequent changes to composition of the bulk spirit, many other reactions would either be limited or enhanced due to kinetic flow relationships. Many other variables need to be considered.[16] Adding tiny amounts or an excess of a specific component or removing something from the milieu is not a simple matter and will affect all subsequent reactions. Nor does studying a reaction in vitro (out of the milieu) necessarily answer the important questions involved in the overall scheme.
Other details concerning oxidation (micro-aeration) of crude spirits were also entertained and covered by Nettleton. Thus, working with wood chips or staves instead of barrels with the application of oxygen, as performed in some micro-distillery-based maturation programs, could work, but is not a new idea. And what control of oxidation is possible with such systems? As will be further detailed in Part 2, numerous oxidation studies have been done for wine in barrel resting or maturation. Not so much yet with respect to spirits — this really needs to be addressed going forward. Micro-oxygenation processes that happen while aging/storing wine in barrels are noted as ensuring that quality red wines achieve their final trait and, moreover, determine aging rates.[17] Will this apply to spirits maturation and final trait quality? Comparable spirit-in-wood maturation experiments and more research are needed!
In addition to the above concepts, processes, and variables, contact of spirit and wood varies depending on barrel size and surface area to fill/content volume and upon the use of wood powders, chips, staves (smooth, rough, or with ridges or grooves), discs, etc. Extraction of components and chemical reactions also depend upon the proof of the spirit, ethanol-to-water ratios, and congeners present. Barrel size has been evaluated in spirit maturation experiments along with extraction rates for accelerated aging of wines and whiskeys.[18] [19] [20] [21] [22] [23] Parker covers the benefits of using small barrels with increased barrel surface area per volume of spirit and the use of oak staves inserted into barrels on RedHeadBarrels.com.[24] A much more serious discussion concerning small barrel maturation and conditions was presented by Jeffery and Berglund.[25] The basics of maturation in wooden barrels was also detailed recently.[26] There is much more to come in Part 2 on alternative wood species and chips, staves, powders, and more in place of barrels and maturation.
Back in time, Nettleton had also noted the use of different sized casks, strengths on bonding, and warehouse conditions. To show there is nothing new under the sun (at least when it comes to what craft distillers think of as modern ideas), Nettleton also notes that “Every conceivable method for imparting flavour and ‘age’ is recommended; previous proposals appear again dressed up somewhat differently: these are agitation processes, oxidation, treatment in vacuum, treatment with chemicals, with flavouring ethers, with electric light, ultra-violet rays, X-rays, &c.” Everything except playing Beethoven and heavy metal music to the slumbering casks! One caveat is that some of the methods covered by Nettleton might be considered as simply varying warehouse maturation conditions rather than rapid-aging machines or methods.
Significantly, Nettleton also observes: “Storage in casks, especially in wine casks, masks the true effects of natural maturation.” It is again important to note that much wine maturation research work has been done, but little directly with spirit in wooden barrels, and that work with spirit in prior-fill barrels (or reused barrels) could be a variable process, as already alluded to above, to watch carefully in terms of product consistency and maturation profiles. Lessons are being learned from the wine industry that may apply to our coverage of spirits maturation.
“But storage in bulk in vessels made of materials impervious to air and moisture, such as earthenware or metal, would not be comparable to cask-storage; it is doubtful whether even prolonged storage under such conditions would afford any evidence of change traceable by chemical analysis,” wrote Nettleton. Fair warning for studies of systems that are out of the box… er… barrel, perhaps — and why major players still insist on traditional maturation times, as expensive as that might be. A statement by a Government Laboratory official (1908–09) says that “Our knowledge of chemistry (as applied to whisky) is by no means so complete as it should be” (cited on p. 313 by Nettleton). So it is today in this author’s humble opinion! This key topic to be covered with some recent research in the right direction in another installment to come. For now, the limitation of both past and present studies is noted below as presented by Mosedale.[27]
Mosedale’s Tenets
Nearly 35 years ago, the Scottish whisky expert J. Mosedale (thesis available online) posed four guiding principles as to why a study of maturation is complex. Here they are, with brief comments.
“The difficulty in summarizing the effects of oak wood on the maturation of alcoholic beverages reflects the diverse range of disciplines and subjects that it involves, and the numerous approaches and motivations behind the studies undertaken.”
People involved include the forester, cooper, distiller, etc. Craft Distillers, “Rapid Maturation Types.” Relevant subjects include biology, biochemistry, chemistry, engineering, forestry science, mechanics, microbiology, and physics.
“It is perhaps not surprising therefore that there is often a notable lack of clarity in many of the studies that have examined the process of whisky maturation.”
Especially when it takes at least five years to a decade or more to complete a typical experiment! More reviews are needed on the current research as works are presented in so many disparate journals. Couple this with inadequate sensory evaluation programs with their inherent biases.
“Each study tends to focus on a single factor that may influence the maturation process, while frequently failing to control variation of other factors adequately.”
Consider the myriad variables: Natural seasoning of wood — a new term, Secretomics, for the enzymes released from fungi to effect wood macromolecule breakdown. Complex reaction cascades in the toasting and charring of barrel wood. Complex Maillard reactions. Mastery of blending spirits might also have some bearing here. Raw materials, mashing, fermentation. Impact of cask (wood) history on distillate composition has been noted, with chemical markers identified allowing for the discrimination of whiskeys, for example.
“Both the solvent and the conditions under which the extractions from and within the wood occur, influence the resulting composition of the extractive.”
Maturation may be defined as the aging of one type of spirit of a defined composition, in one type of wood — perhaps adding, under “more, or less defined conditions.”[28] Noting that we barely understand traditional maturation, let alone alternative systems. What are we comparing to what here?
A clear comprehension of the tenets above will assist in any further distilled spirits research as will big data collection (OMICS) and holistic thinking. Major distilling companies, cooperages, and spirits research institutes may be harboring important data and findings that are only available to members or staff. A handful of important U.S.-based distilleries publications from 80 years ago are available to us as an important baseline to guide future research efforts. Thereafter, not so much was published from operational distilleries or their research groups in the U.S. or elsewhere.
Maturation Chemistry Summary: OMICS and Overall Production of Distilled Spirits
A complete overview of distilled spirits maturation and the components involved, including solvents, congeners, and wood components, and interactions as understood to date, was presented in the 80 Years articles and used by Tarko, et al., in the 2023 publication. A summary is presented here in three figures.
Figure 1 shows a rendition of reactions involved in the spirit-barrel engine. Figure 2 is an overview schematic of the entire process flow, from raw materials to finished goods, in distilled spirits production and introduces OMICS approaches.[29] OMICS, or big data collection, and the questions posed in the figure may lead to a holistic understanding of consistent and authentic, flavorful, packaged matured brown spirits — traditionally or rapidly matured! All stages affect final product quality and flavor profile, and details from each step or process should form part of a quality control program for the distiller.
Figure 3 then presents an overview schematic of the six component chemistries and associated physicochemical processes involved in spirit-in-wood or spirit-on-wood maturation leading to the data set composite for the maturome and thereby defining maturomics (relate Figure 3 to Figure 1). A complete understanding of all the data to be gleaned from OMICS approaches, terms, definitions, and questions posed will be needed when altering maturation conditions or wood species or type of wood. See Sidebar 1 for a reverse engineering approach to spirits production as pioneered by the late Dr. James Swan, a highly influential consultant to the industry. Maturation and warehouse design and consideration of the environmental conditions which would impact the aging or maturation of the spirit serve as the starting points for product development. Brilliant!
In addition, sensomics approaches, whereby a complete understanding of flavor profiles and the sensory detection and interpretation of all key flavor volatiles that define that spirit style by the human sensory apparatus, will be needed to satisfactorily compare a traditionally matured product versus a rapidly aged or post-production/maturation “tweaked” product.
Summary
The reader is encouraged to go back and read the three-piece article published in Distiller in 2017/18, or find the e-book on Amazon, which includes an added discussion of another major set of key topic references. Review the details first on the ethanol/water solvent properties, then how congeners affect solvent structure and how solvent affects the suppression or release of volatiles from solution in maturing spirit or the glass being held by somebody consuming their favorite whiskey or rum. The reader is also encouraged to review the basics of wood seasoning and cooperage operations, toasting, and charring. Refer to Figures 1–3 here to view the complexity of the “in-barrel” spirit-in wood maturation engine or maturome. Furthermore, a consideration of the four principles outlined by Mosedale will illustrate why this is a complex topic to tackle, at least in a timely manner. Some history and brief details on rapid-maturation systems here will be complemented by much further detail in Part 2 of this treatise in the next issue of Distiller, wherein we will try to address if the next installment will need to go beyond 136 years before craft.
SIDEBAR:
Dr. James Swan: Putting the barrel or wood before the raw materials.
As seen in this article, the complexity of seeking answers to maturation — rapidly attained or not (traditional time frames) — encompasses the entire spirits production process. We can call this big data or “multiomics” in today’s lingo. Many distillers do not take this holistic view, but it was supposedly not lost upon the late Dr. James Swan. It has been suggested that, when invited to help establish a new distillery in India, for example, he first envisioned how things would mature in a rickhouse under Indian climatic conditions. Then Swan reverse-engineered the process from maturation all the way back to water and raw materials.
Such a full approach may not be necessary for “rapidly” maturing raw white spirit already consistently well produced by a distiller. However, it is necessary to understand how that spirit matures in wooden barrels and assess all the conditions and multitude of variables at play, which may then allow the maturation to take place under alternative system conditions. That is the challenge ahead.
Physics, chemistry, thermodynamics, kinetics, chemical flux, biochemistry, microbiology, sensory evaluations, and more will all be important subjects of consideration. See Figures 1–3 for the generalized scheme of questions and concepts the distiller must consider in designing and building their own system of production. Even if the details are not correct or fully represented, the idea here of reverse engineering a concept is quite germane to looking at alternate maturation or production process schemes. A study of the composition and flavor profile of a spirit related to how it got there is the key here.
Figure 1. Key principles involved in the Maturome – The spirit-in-wood maturation process.
Some key concepts, processes, and terms are needed to comprehend the complexity of the “in-the-traditional barrel” spirit-in-wood maturation engine. How such a system can be replicated in an open or non-wood-based vessel, along with wood chips, staves, powders, etc., or with synthetic chemical mixtures, and then lead to a near-identical flavor profile spirit is an incredibly intricate system to fathom. Big data manipulation is required, covering raw materials through processing to maturation. Complex, well-designed experiments are still needed to fully understand spirits production and maturation. Sensory evaluation and sensomics (holistic data collection and avoidance of many biases) and full flavor profiling are also needed to compare traditional with alternate maturation systems. Some progress is being made; however, a lot of research is still needed in this fascinating arena. Some details are provided here and in Part 2 of this treatise.
Figure 2. An overview schematic of process flow in distilled spirits production and introducing the OMICS approaches that may lead to holistic understanding of consistent and authentic flavorful packaged matured brown spirits – traditionally or rapidly matured!
This figure presents an overview of all stages in distilled spirits production, with relevance to brown spirits production. Such key concepts, processes, and terms are needed to comprehend the complexity of the “in-the-traditional barrel” spirit-in-wood maturation engine and to understand potential alternative maturation schemes. Some terms are not covered in any detail or at all in the text, but the diagram provides a global list of terms applying to OMICS/big data approaches to a holistic understanding of the complex spirits production program (4, 18). All stages apply to delivering a quality flavorful product. That said, for this topic of discussion the most pertinent sections are: Distillation for quality of raw white spirit — the solvent-congener mix — Maturation (see also Figures 1 and 3), and Dumping/Filling/Packaging. Mastery of blending spirits could also eliminate minor differences noted between traditionally matured and rapidly matured spirits. Introducing OMICS (the overlapping shapes) and some of the modern laboratory methods used to study the composition of spirits and the application of sensory evaluation methods — instrumental or human-based — are also included here. Further details can be gleaned from many of the references cited in the body text.
Figure 3. An overview schematic of the six component chemistries and associated physicochemical processes involved in spirit-in-wood or spirit-on-wood maturation leading to the data set composite for the maturome and thereby defining maturomics.
To compare spirit-in-barrel vs. alternative spirit-in-contact-with-wood maturation systems, we must understand a complex set of extractions, reactions, interactions, molecular collisions, proximity attractions, trapping of molecules, oxidations, and synergistic and antagonistic reaction concepts and kinetic and chemical fluxes. The barrel system is an engine — an enclosed, though semi-permeable “cell,” at least as it relates to intake and release of gasses and smaller volatile molecules. Systems open to the air, such as those using different material vessels or contact with wood as chips, staves, etc., must act differently. Many of the concepts and processes involved here are outlined in this figure. Again (see legend to Figure 2), mastery of blending spirits could play a key role here. Additional references supply information on the aging and oxidation reactions and will be covered again in more detail in Part 2 — including for baijiu and rum.
[1] Spedding, G. 80 Years of Rapid Maturation Studies: Why Are We Not There Yet? American Distilling Institute, 2021. ASIN: B091KH4ZN3. Kindle.
[2] Barnard, A. The Whisky Distilleries of the United Kingdom. Edinburgh: Birlinn Limited, 2008. Reprinted 2017, 2018. First Published 1887 by Harper’s Weekly Gazette.
[3] Nettleton, J. A. The Manufacture of Whisky And Plain Spirit. Aberdeen: G. Cornwall & Sons, 1913. Reprint, Pitlochry: Classic Expressions, 2009.
[4] See “Equilibrium and Le Chatelier’s Principle,” CompoundChem.com, compoundchem.com/wp-content/uploads/2023/10/Reversible-Reactions-and-Equilibrium-2023.pdf, and the entry for “Le Chatelier’s Principle” on Siyavula.com.
[5] See United States Patent 9637713, May 2, 2017, https://patentimages.storage.googleapis.com/bc/04/49/5a8a235dba40f1/US9637713.pdf.
[6] “Newly Issued Patents Will Chemically Age Rum and Whiskey 20 Years in 1 Week,” Distillery Trail, Apr 3, 2017, https://www.distillerytrail.com/blog/newly-issued-patents-will-chemically-age-rum-and-whiskey-20-years-in-1-week.
[7] Spedding, G. “OMICS and the Future of Brewing and Distilling Research.” In Chemistry of Alcoholic Beverages, ACS Symposium Series, vol. 1455. American Chemical Society, 2023. DOI: 10.1021/bk-2023-1455.ch007 10.1021/bk-2023-1455.ch007.
[8] Del Alamo-Sanza, M., and I. Nevares. “Oak Wine Barrel as an Active Vessel: A Critical Review of Past and Current Knowledge.” Crit Rev Food Sci Nutr 58, no. 16 (2018): 2711–2726. DOI: 10.1080/10408398.2017.1330250.
[9] Echave, J., M. Barral, M. Fraga-Corral, M. A. Prieto, and J. Simal-Gandara. “Bottle Aging and Storage of Wines: A Review.” Molecules 26, no. 3 (2021). DOI: 10.3390/molecules26030713.
[10] Krüger, R. T., A. Alberti, and A. Nogueira. “Current Technologies to Accelerate the Aging Process of Alcoholic Beverages: A Review.” Beverages 8, no. 65 (2022). DOI: 10.3390/beverages8040065.
[11] Mills and Barr, 1890, cited by Nettleton.
[12] Michela Centinari,”Assessing and Managing Potassium Concentration in the Vineyard,” Penn State Extension, May 4, 2023,
https://extension.psu.edu/assessing-and-managing-potassium-concentration-in-the-vineyard.
[13] Spedding, G. “OMICS and the Future of Brewing and Distilling Research.” In Chemistry of Alcoholic Beverages, ACS Symposium Series, vol. 1455. American Chemical Society, 2023. DOI: 10.1021/bk-2023-1455.ch007 10.1021/bk-2023-1455.ch007.
[14] United States Patent 6506430, Jan 14, 2003, https://patentimages.storage.googleapis.com/87/e6/7f/7eca86acac2e82/US6506430.pdf.
[15] Patent US6703060B1 en (9).
[16]See below under “Mosedale’s Tenets” for more on the limitations of studies and ways around the problems (10).
[17] See 11 regarding wine aging technology.
[18] Jeffery, J. D. E. “Aging of Whiskey Spirits in Barrels of Non-Traditional Volume.” MA thesis, Michigan State University, 2012.
[19] Jeffery, J. D. E., K. Arvid, and Berglund. “Extraction of Wood Constituents from Non-Conventional, Small Whiskey Barrels.” J Food Processing & Beverages 4, no. 1 (2016):7. DOI: 10.13188/2332-4104.1000017.
[20] Kupetz, M., M. Pistel, F. Lehnhardt, and T. Becker. “Woodbased Flavorings in Spirits (Part 1): The Basics.” Brauwelt International V (Oct 18, 2022): 333–338. https://brauwelt.com/en/topics/quality-assurance/644904-woodbased-flavorings-in-spirits-part-1-the-basics.
[21] Del Toro, N., Rial J. Ayan, J. Yperman, D. Vandamme, R. Carleer, and Sariol H. Crespo. “Optimized Criterion Based on the Surface Area to Volume Ratio for Wood Casks Re-Filling Time Calculation during Long-Term Rum Maturation Process.” J Food Processing & Beverages 10, no. 1 (Sept 2023): 9.
[22] Tarko, T., F. Krankowski, and A. Duda-Chodak. “The Impact of Compounds Extracted from Wood on the Quality of Alcoholic Beverages.” Molecules 28, no. 620 (2023). DOI: 10.3390/molecules28020620.
[23] Oberholster, A., B. L. Elmendorf, L. A. Lerno, E. S. King, H. Heymann, C. E. Brenneman, and R. B. Boulton. “Barrel Maturation, Oak Alternatives and Micro-Oxygenation: Influence on Red Wine Aging and Quality.” Food Chemistry 173 (2015): 1250–1258. DOI: 10.1016/j.foodchem.2014.10.043.
[24] Parker, “Accelerated Aging: How Long to Age Whiskey in a Small Barrel,” RedHeadBarrels.com, Mar 31, 2023, redheadoakbarrels.com/accelerated-aging-how-long-to-age-whiskey-in-a-small-barrel/.
[25] Jeffery, J. D. E., K. Arvid, and Berglund. “Extraction of Wood Constituents from Non-Conventional, Small Whiskey Barrels.” J Food Processing & Beverages 4, no. 1 (2016):7. DOI: 10.13188/2332-4104.1000017.
[26] Kupetz, M., M. Pistel, F. Lehnhardt, and T. Becker. “Woodbased Flavorings in Spirits (Part 1): The Basics.” Brauwelt International V (Oct 18, 2022): 333–338. https://brauwelt.com/en/topics/quality-assurance/644904-woodbased-flavorings-in-spirits-part-1-the-basics.
[27] Mosedale, J. R. “Effects of Oak Wood on the Maturation of Alcoholic Beverages with Particular Reference to Whisky.” Forestry 68, no. 3 (1995): 203–230.
[28] Del Toro, N., Rial J. Ayan, J. Yperman, D. Vandamme, R. Carleer, and Sariol H. Crespo. “Optimized Criterion Based on the Surface Area to Volume Ratio for Wood Casks Re-Filling Time Calculation during Long-Term Rum Maturation Process.” J Food Processing & Beverages 10, no. 1 (Sept 2023): 9.
[29] Spedding, G. “Oh, Distiller, Distiller — How Does Your Complex Spirit Arise? Only Fully Understood by OMICS I Surmise.” Artisan Spirit 44 (Fall 2023): 86–90.
