Monday, August 6, 2012

What distillation is

Distiller's Log, Feb 4th 2012

There isn't much construction yet as we're waiting on inspectors, electricians etc, so I thought I would do a technical post. I will be posting with info on our spirits, but also on distillation, aging, tasting, fermentation, here's one on distilling.

Distillation is how you turn wine or beer into brandy, whiskey, or vodka. It's defined as the separation of volatile compounds by their boiling points. I'll start out with high school chemistry and take it from there. The boiling point of a mixture falls somewhere between the individual boiling points of the components within the mixture. The greater the proportion of one component the closer to it's boiling point will be the mixture.

Boiling point Ethanol: 78.6C
Boiling point Water:   100C
All ethanol distillation occurs with the vapor and the liquid somewhere between these two temperatures.

A still is basically a pot with any number of things hooked up to it. In the simplest stills there's a helmet (a big open copper top)  and then a condensor (something with cooled metal surface for the vapor to condense on). These are called alembic stills and are used to make Scotch and other whiskies, rum and many of the more flavorful spirits. They are made of copper because copper is a reactive metal and is great at removing unpleasant compounds from the vapor. Alembic stills are excellent for flavored spirits as they don't have much tech attached for purification and allow a lot of flavor to come through. The downside is that there isn't much control or ability to alter the distillation process. It produces what it's going to produce and most of your product is controlled by the fermentation process.

A more complex setup would have a column of some kind after the pot and helmet or rather than a helmet. The column has plates inside, on which the vapor condenses and then revaporizes. Each time this happens the percentage of alcohol in the vapor goes up. This is called rectification. Given enough plates you get 96% alcohol, which is the highest alcohol you can get with distillation alone. A short column of 3 or 4 trays can be used to make more lightly flavored whiskey than an alambic still might make, or it can be used to make a spirit that is very light and clean, with high rectification. The short columns are indespensible for the production of eau de vie, brandy, and other fruit fermented spirits, and are also used for whiskey, rum, etc.

In the course of distillation there are a series of cuts made chronologically. These are made differently in different traditions but the principles are the same.

1. Heads cut
Mostly consisting of ethanol and water, the heads cut is the first stuff to come out of the still and has a collection of other components that have lower boiling points than ethanol. Acetaldehyde, Acetone, Ethyl acetate, Methanol among others have flavor and aroma characteristics you might describe as fruit, floral, finger nail polish remover, marker, or solvent. Although some of those sound strange for something you drink, they are an important part of the flavor/aroma profile of many spirits. Most of this early cut is removed but low concentrations of these compounds are either included or reintroduced to later distillations. The bulk of the heads cut is just disposed of. We use ours as a spray on sanitizer.

2. Hearts cut
This is the spirit itself. The distiller makes this cut by smell and taste and this is the only part of the distillation you will ever drink. Many distillers make a big deal about only including the hearts cut of a distillation in their bottle. If they include anything else no one will buy what they're selling.  The hearts is also primarily ethanol and water but there are hundreds of compounds that can be solubilized in either the water or the ethanol to provide flavor and aroma.

3. Tails
The tails cut is disposed of like the heads, or rectified to neutral for use in gin or for fortification. This cut has many alcohols in it you wouldn't think you'd want such as propanol, butanol, isoamyl alcohol. These sound terrible, but if you drink whiskey, rum, or basically anything other than vodka, you are enjoying the lovely flavors these alcohols provide. Again this cut is made at the distiller's discretion and anything that gives you a serious headache had a tails cut that was too generous.

In the figures below you can see some data collected during a vodka run. The x-axis is time and the y-axis is concentration. What you're looking at is the change in congener (heads and tails) concentration during the vodka run. The heads figure stops at 250min because not much other than ethanol and water are coming out until figure 2 starts around minute 620.  This data was collected using Gas Chromatography which is a great way of looking at these kinds of things.

The heads cut was finished at about 35 minutes and the tails cut started at 640. On the heads side clearly some of these compounds make it into the distillate but by the time they are diluted into the hearts, the concentrations are very low.

While the distillation and the cuts are very important many mistakes are made in the fermentation. This is really where all of the flavors are made and by the time it's reached the still, many serious fermentation faults just can't be fixed.

There are other things within the alcohol water matrix. Remember those two temps above between which all ethanol distillation occurs? Some compounds with much higher boiling points can be found in spirits because they are soluble in one of the liquids. For example fatty acids with boiling points as high as 200C can be found in whiskey because they are soluble in alcohol, so they travel over with the vapor. These can provide flavor and/or mouthfeel and are important in aged spirits. Another example would be phenolics from the grain. These travel over and produce the grain flavors, and tasting notes like spice, caramel, smoke, and many more.

Thanks for reading,
Head Distiller