Colloidal Stability and Whiskey (and other aged Spirit) Hazes. Gary Spedding, PhD. BDAS, LLC, Lexington, KY

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1 Colloidal Stability and Whiskey (and other aged Spirit) Hazes Gary Spedding, PhD. BDAS, LLC, Lexington, KY At BDAS, LLC we are frequently asked about hazes and particulate formation in craft spirits. While there can be several causes, and the precipitates seen may be of different chemical compositions and identities, we focus here on the so called chill haze issue. Some craft spirits producers want to distinguish themselves by using a specific artesian spring/well source. While this might be acceptable for the actual spirit production for reasons we will not delve into here, these spring waters harbor too high a concentration of certain mineral ions (calcium and magnesium of key concern) for the water to be used for spirit dilution purposes. This can result in mineral hazes. But I digress here so let s get to colloidal stability. Colloidal stability. As colloidal stability is a term pertaining to whisky and other spirits this important topic is briefly entertained here. Over time many alcoholic beverages are likely to form a haze or show a light precipitate or may exhibit a potential for significant turbidity. The turbidity is caused by colloidally dissolved substances. As this issue of colloids and stability is an issue that is confusing to many a few definitions are also in order here before proceeding. A colloid is a homogeneous, non-crystalline substance consisting of large molecules or ultramicroscopic finely divided particles (1 to 1000 millimicrons [= 10-9 meter or nanometers] in size) of one substance dispersed within a continuous medium in a manner that prevents them from being filtered easily or settled rapidly. Colloids include gels, sols, and emulsions; the particles do not settle and cannot be separated out by ordinary filtering or centrifuging like those in a suspension. The term also refers to the particulate matter so dispersed. Mayonnaise and blood are both examples of colloids. The colloidal stability of beer, for example, refers to its propensity to form non-biological hazes due to interactions between beer components - principally polyphenols and proteins leading to formation of visible precipitates; colloids in beer can take the form of gelatinous (jelly like) masses. The issue with respect to spirits follows. Whiskies and other aged spirits are also subject to the physical and chemical principles related to colloidal stability and the production of colloidal particles. Grain based spirits may see the contribution of lipids via extraction from the barley or other cereals and these carry through all the processes and to the maturation phases. Other lipid class molecules the sterols are derived from the wood and are related to the largest class of plant derived chemicals known as the terpenoids. The Scottish whisky industry in particular is known for the use of the chill filtration process to reduce the propensity for chill haze formation. This will apply to Bourbon whiskey production also. When whiskies are above 46% ABV at around C no hazes or major effects on clarity will usually be evident. However, and for example when reducing aged spirit to bottling strength the spirit may become cloudy (hazy) reducing its visual appeal to the consumer. Based on the actual composition different whiskies will also have different levels of lipids and so some will show the issue of chill-haze or clouding more intensely and/or more often than others. The chemical explanation for the appearance and disappearance of cloudiness in spirits such as whisky is related to hydrogen bonding and to so called hydrophilic (water loving) and hydrophobic (water hating) 1

2 properties of water, ethanol and lipids. Lipids (from the fat class of molecules) consist of a portion known as the head and a portion known as the tail. The head portion, which is hydrophilic meaning it prefers to be in contact with like-minded molecules (those that are water or water-like or loving) is characterized by an electrically charged hydroxyl (OH) group. The tail group which hates water (water fearing = hydrophobic) is composed of one to three variable length hydrocarbon chains. Figure 1: Structures of Phospholipids and Steroid Lipids Again we see the different solvent properties of water and ethanol at play here as in other aspects of distilled spirits chemistry including congener flavor issues. With respect to fatty acids, the dominance of the long hydrocarbon chains (see Figure 1) prevents the oil (many fats at typical room temperatures are oils) from mixing with water. However, ethanol also has a hydrocarbon chain and an OH group yet mixes easily with water. The carbon chain is so short it is not an issue with respect to its interaction and association with water (and in fact ethanol and water are mixable miscible in scientific terms - in all proportions). In fact the tails of ethanol slide into the structural matrix of water and this formation of water and ethanol leads to a volume contraction of simple (binary) ethanol water solutions. The short chain of ethanol is also chemically compatible with long hydrocarbon chains of lipids and allows the mixing of them with ethanol. The ethanol is said to participate in the solvation of both water and fats and can help keep fats in solution under certain conditions of course. This phenomenon is both dependent upon the ethanol concentration and temperature and structural perturbations by other volatile and non-volatile species in distilled spirits. Much is yet to be understood in this matter. In addition to hydrophobic and hydrophilic interactions (molecular forces of attraction and repulsion) ethanol and water structure is held together by hydrogen bonding and this affects the solvation (the 2

3 solvent) properties and potential for interaction of the two species water and ethanol and their bonding with other components. In whiskies, as the ethanol concentration drops (during proofing and bottling for example), at some point it can no longer assist keeping the oil and water together and separation will occur. This happens somewhere around 46% ABV at C. At much lower temperatures even the higher concentrations of ethanol cannot prevent the separation. Hence the chill-haze separation or chill-proofing operations sometimes implemented by whisky/bourbon distillers. When lipids and water are not compatible together the lipids will try to push themselves together and away from water (conversely it could be said that water tries to aggregate and push away the lipids). Lipids will form spherical structures called micelles where the lipid molecules orient themselves to present the hydrophilic (water loving) head group exposed to water while burying their tails in the center of the sphere to form a hydrophobic core. The formation of the micelle structure is a fundamental property that helped give rise to biological systems. See Figure 2. Figure 2: Structure of a micelle hydrophobic hydrocarbon chains are buried in the interior and the hydroxyl hydrophilic head groups are exposed to water; think of as a sphere. While only one hydrocarbon chain is seen attached to the head groups, in biological membranes they are usually existing with two hydrocarbon chains per head group. Now these micelles are very small but when masses of them form they scatter light which results in a cloudy suspension. It is such a suspension of solid particles in a liquid that we referred to above as a colloid. Colloids are not easily filtered out as discussed above. However, such particulate matter can be removed by chill filtration. Now different lipids have different length hydrocarbon tails the length determining solubility. The longer hydrocarbon chains make the lipids less soluble and these form micelles just below 46 % ABV. Other lipids will only form micelles with a further drop in ethanol content. In lipid chemistry this is also dependent upon the amount of the lipid present and is known as the critical micelle concentration. Different whiskies, based on raw materials and processing, will harbor different compositions and concentrations of lipids and so a one size filtration operation may not fit all situations. 3

4 Some non-chill filtered whisky batches will be troubled with haze issues while others won t. And sometimes hazes could be caused for other reasons. The hazes will be dependent upon not only lipid content and composition but also on the ethanol concentration, temperature, possibly on mineral content, and sometime just time itself allowing for the aggregation of molecules. The Chill filtering and haze process is not detailed here references can be provided upon request. A final point to make concerns the presence in mature whiskies (and including Bourbon whiskies) of sterols which may also precipitate upon chilling and, as we have seen recently with many calls, even as stored at room temperature (20-25 C). Several steroid based lipids (see schematic in Figure 1) which are related to the better known cholesterol have been identified in Bourbon; campesterol, stigmasterol and beta-sitosterol included in the list and even sugar derivatives such as sitosterol-d-glucoside. Figure 3 summarizes some details on fatty acids and sterols as taken from an ACSA seminar presented by Gary Spedding and Johnny Jeffrey. 4

5 Figure 3. Organic hazes a summary of the fatty acids and sterols which can be responsible for hazes in whiskies. Summary: In summary based on a number of requests we see on the sudden appearance of hazes in aged spirits the above review has been provided by way of an explanation of fatty acid and sterol based hazes. These can sometimes be remedied by a chill filtration process. However, many craft distillers and some major Scottish whisky distillers prefer not to touch filtration as it may rob the spirits of some flavor components. The process of chill filtration and details may be found elsewhere though one final note is that filters used in the process can cause metal ion-induced hazes if they carry high amounts of calcium and or magnesium ions into the spirit. This is an issue which could be the focus of its own article and for now we end the present discussion. [As always references and further input available upon request) Gary Spedding, Ph.D. for Brewing and Distilling Analytical Services, LLC, KY. August 27 th,