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FIGURE 1
STRUCTURES of
PHOSPHOLIPIDS and
by resin treatment. It is to be noted that it can take several months to
get calcium oxalate formation in product and the higher the proof the STEROID LIPIDS
higher the risk of formation. Some whiskies, filtered through charcoal
prior to maturation, can also pick up calcium from the wood and here Different solvent properties of water and ethanol are at play here as
the calcium levels may be reduced using ion-exchange treatments. in other aspects of distilled spirits chemistry. With respect to fatty acids,
the dominance of the long hydrocarbon chains pre-
Interesting historical accounts on activated carbon treatment of vents the oil from mixing with water. (Many fats
HEAD
whisky may be found in works by Dudley (1908) and by Williams and at typical room temperatures are oils.) However,
Fallin (1943). Diatomaceous earth (DE) filter pads are used in some TAILS ethanol also has a hydrocarbon chain and an OH
distilleries. As DE is itself made up of tiny calcium-based “sea shells” group yet mixes easily with water. The carbon
it should be obvious that proper quality specifications should be in play chain is so short it is not an issue with respect
HYDROPHILIC HEAD to its interaction and association with water
if this filtration product is used.
CH 2 —N+(CH 3 ) 3 (and in fact ethanol and water are mixable
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The oxalates issue has been resolved by the major distilleries but is | CH 2 – miscible in scientific terms - in all propor-
O |
a very complex topic as recent brewing research has shown. Anything O—P—O tions). In fact, the tails of ethanol slide into the
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O |
that can affect the delicate solubility equilibrium dealing with oxalates CH 2 —CH—CH 2 structural matrix of water and this formation of
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O O water and ethanol leads to a volume contraction of
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(from grains/cereals) and calcium ions (from grains, barrel wood C=O C=O simple (binary) ethanol-water solutions. The short
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and water) in solution can tip the balance in favor of precipitation. CH 2 CH 2 chain of ethanol is also chemically compatible with long
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CH 2
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CH 2
The common thought that limestone water is good for bourbon CH 2 CH 2 hydrocarbon chains of lipids and allows the mixing of
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CH 2
CH 2
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production conveys a bit of myth here and it is best to use dilution FATTY ACID CHAINS CH 2 CH 2 them with ethanol. The ethanol is said to participate in
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CH 2
CH 2
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water absolutely-free of organic matter and minerals to help promote CH 2 CH 2 the solvation of both water and fats and can help keep
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CH 2
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CH 2
=
stability. Though it must be remembered that calcium and magnesium CH 2 CH 2 | fats in solution under certain conditions of course.
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CH 2 CH 2 This phenomenon is both dependent upon the ethanol
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ions are important in fermentation and yeast health so understanding CH 2 CH 2 |
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CH 2 CH 2 | concentration, temperature and structural perturba-
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their levels throughout production is also quite important. CH 2 CH 2 | tions by other volatile and non-volatile species in
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CH 2 CH 2 |
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However, both the calcium ions and oxalate levels need to be CH 2 CH 2 | distilled spirits. Much is yet to be understood in
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CH 2 CH 2
known in the spirit to begin with to ensure they are not too high in HYDROPHOBIC TAIL this matter. In addition to hydrophobic and
concentration at bottling time (see issues related to all this below). It hydrophilic interactions (molecular forces of
attraction and repulsion) the binary solvent
is stated (personal communications) that bourbon has higher levels of – ethanol-water structure is held together by
oxalic acid than for Scotch or Canadian whiskies in part supposedly hydrogen bonding and this affects the solvation (the
due to the use of new cooperage; this idea or concept possibly bears solvent) properties and potential for interaction of the
further investigation. Theoretically, therefore, lower calcium in dilution two species – water and ethanol, and their bonding with
water or “cut-water” is required for bourbon whisky production. other components.
In whiskies, as the ethanol concentration
Keeping calcium as the limiting reagent should keep the oxalates in drops (during proofing and bottling for
solution unless something else changes the solubility equilibrium. example), at some point it can no longer
PHOSPHOLIPIDS assist keeping the oil and water together
Summarizing some general points and separation will occur; as noted above
this happens somewhere around 46%
from the 1960’s Warwicker papers HYDROPHILIC HEAD ABV at 20-25 °C. At much lower
Extracts from oak wood include some calcium — contributing perhaps POLAR HEAD GROUP temperatures, even the higher
concentrations of ethanol cannot
as much as 7 ppm! Barrel extractives thus contribute to deposition and RIGID prevent the separation. Hence the
double ion-exchange was shown to alleviate the problem. Magnesium PLANAR requirement for chill-haze separa-
STEROID
ions from filter pads can throw a deposit as can calcium picked up RING tion or chill-proofing operations
from filter pads and filter aids. Thus, for chill filtration, filter pads, filter STRUCTURE as sometimes implemented by
aids and DE should be low in these alkaline earth metals. Zinc and whisky/bourbon distillers.
When lipids and water
aluminum salts can cause similar results. Deposition increases as pH NON-POLAR are not compatible together
rises from 4.5 to 4.9 according to interpreted results of the experiments STEROID-BASED HYDROCARBON the lipids will try to push
TAIL
performed in the 1960s (Warwicker, 1960; 1963 a, b). In general, the LIPIDS themselves together and
critical pH for deposition seems to be 4.9 while above pH 6.0, there HYDROPHOBIC away from water (converse-
is no deposition. Simple evaluations of pH in distilled spirits are to be TAIL ly it could simply be said
that water tries to aggregate
recommended, along with observations, over time, of the clarity of the and push away the lipids);
packaged product. Perhaps now, 50 years on, new investigations into this driving force, direction and extent is all subject to thermodynamic
this pH variable might be warranted. At the very least a routine testing principles. Lipids will form spherical structures called micelles where
of calcium, magnesium, iron and zinc concentrations in process water the lipid molecules orient themselves to present the hydrophilic (water
and final product might also, therefore, be recommended. loving) head group exposed to water while burying their tails in the
Chill proofing with subsequent filtration will improve the stability center of the sphere to form a hydrophobic core. The formation of the
“micelle structure” is a fundamental property that helped give rise to bi-
ological systems. See Figure 2 for a diagram of a micelle.
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