Science with Richard Bleil
A friend of mine posted a meme on her social media account asking if you would take an inordinately large sum of money if it meant you could never buy alcohol again. In my comment, I asked if that included purchasing alcohol for non-consumption purposes for use as a solvent. As it turns out, alcohol is a superb solvent. One of her friends replied, saying nobody had drunk alcohol in her house for many years, but that she normally has denatured alcohol on hand as, yes, a solvent.
Alcohol is a fabulous solvent. Less polar than water, it will dissolve some substances that would not be soluble in water, but because alcohol dissolves in water, it’s also easily washed away when done. And, if it’s not denatured, it’s also a great solvent for extracting vanilla from vanilla beans. I have denatured alcohol here, and 190 proof alcohol that is not denatured.
There are a few things to unwind in that previous statement. First, “denatured” means “made intentionally toxic.” Alcohol is denatured (often with methanol) as a guarantee that it cannot be consumed. Denatured alcohol is not taxed because it cannot be used in beverages. Methanol is very poisonous, so if you drink denatured alcohol, the best you can hope for is to be permanently blinded.
“Proof” is a measure of concentration in alcohol. Proof is always twice the percentage alcohol, so 190 proof is 95% alcohol. This is nearly the highest concentration you can get, but the reason is unknown to many people. I’ve heard it said that it’s impossible to have 100% alcohol because it cannot exist in liquid form, but this is wrong. I’ve worked with 100% (200 proof) alcohol myself, but it’s not common in labs. Because it’s 100%, it’s impossible to denature 200 proof alcohol because anything you add will drop the percent of alcohol. This form of alcohol is taxed, and therefore more expensive than denatured alcohol, but there are some experiments that actually cannot use denatured alcohol. For example, I would not used denatured alcohol to extract vanilla.
The reason that 200 proof alcohol is so hard to find is actually because of the distillation process. See, every time alcohol is distilled, some water co-distills with the alcohol. During subsequent distillation, the ratio of distilled alcohol to water increases. At about 96%, alcohol forms what is called an “azeotrope”. At this concentration, exactly the same ratio of water co-distills with the alcohol at each new distillation. In other words, you can re-distill the azeotrope as much as you like, but the concentration of alcohol will no longer change with the distillation.
That’s not to say that there aren’t ways to get higher concentration alcohol from the azeotrope. Heck, there must be a way or I could have never worked with 200 proof alcohol in the lab. One of the more common ways to increase alcohol concentration is, rather than distillation, simply remove the water from the azeotrope. This is often done with the addition of a desiccant, not unlike the desiccant that sometimes accompanies new purchases. A desiccant is simply a chemical that absorbs water. In packaged desiccants that come with new purchases absorbs water from the air, but they will also absorb water from solutions like alcohol. So, addition of a desiccant to an azeotropic solution of alcohol will absorb the water in the alcohol, “breaking” the azeotrope. Then, the desiccant is simply filtered out, after which the alcohol is distilled, and each subsequent distillation will further increase the purity (the concentration) of the alcohol.
The ironic thing about the 190 proof alcohol I have (the one that is not denatured), the label used to say that it is not intended for human consumption. The exact wording was something like, “Not for consumption unless mixed with another non-alcoholic beverage”. Apparently they’ve taken this wording out, and replaced it with “Extract, Infuse, Fortify.” It is a great solvent, as I’ve said, to extract vanilla from the bean. “Infuse” means to make something alcoholic that is not otherwise. For example, You can infuse it in orange juice to make an alcoholic beverage. “Fortify” means to add it to another alcoholic beverages to increase the amount of alcohol in it. A fortified wine, for example, is wine (already with alcohol) with added liquor to make it stronger. In a sense, it is still saying that it is not intended for human consumption.
Another way to increase alcohol concentration is through freezing the alcoholic beverage. Fermented beverages are made by the action of microbes on sugar containing beverages. The colonists used to love their fermented cider, but, unfortunately, the alcohol is a waste product of the microbes consuming the sugar. Eventually the concentration of alcohol becomes high enough to kill the microbes, but this level of alcohol was not strong enough for the palates of the colonists. Distillation was known, but with such poor fire fighting technology, the risk of fire could burn down entire towns and was not worth the risk. Instead, they would put the cider in wooden barrels and leave them out in the winter in hopes of very low temperatures. As the water in the barrel would freeze, it freezes as pure water with no significant alcohol in it. They would break up the ice with axes and take it out, removing water and leaving behind cider with higher alcohol concentration. a