If you, as a craft distiller, want to make the best spirits possible, you need to have full control over all variables. If you want to make the beste spirits consistently, you need even more control. This iStill Blog post dives into the influence of air pressure, how it can screw up your run, and how iStill’s innovations help solve the issue.
The influence of air pressure on distilling
When distilling spirits, we aim to first concentrate the alcohol by a fast stripping run. Thereafter, a slower finishing run is performed where the heads, hearts and tails fractions are separated by means of boiling point differences between those fractions. Heads come over at lower temperatures than hearts and hearts boil off at lower temperatures than tails.
From the above alinea it becomes clear that boiling points are key to good cuts management. Just as good cuts management is essential to bring over the right flavors and create that above top shelf spirit you are after.
So good cuts management, essential to the creation of great spirits, depends on boiling points. And guess what? Boiling points depend on air pressure! And since air pressure is not a given, not a set parameter, it creates variability in your cuts, translating into potentially sub-standard quality drinks.
Air pressure structurally differs between locations. As a general rule: the higher altitude your location is, the less air sits above your still, the lower the air pressure is. Air pressure is also variable in time. When a new weather front moves in, air pressure will rise or lower. The issue with this? As a distiller you are constantly confronted with different air pressures, translating to different boiling points. Between runs and during runs.
Ethanol, for example, boils at 78.3C or 173F. At standardized sea level air pressure that is. Higher air pressure pushes boiling points upwards by up to 0.5 degrees easily. Lower air pressure lowers ethanol’s (and other components) boiling point.
Air pressure sensor old style …
How air pressure can screw up your distillation run
Say that you follow a set of standard cut points for heads, hearts and tails of your whiskey run. Here is what they may look like:
- Heads are collected until 80C;
- Hearts are collected until 95C;
- Tails are collected until 98C.
You came to the above cut points, because that’s how you liked your first whiskey run. Why not repeat that, right? Well … because the air pressure variance will hamper your ability to arrive at the same results.
Imagine the following real life example. You did your first whiskey finishing run at sea level and – by coincidence – at standard air pressure. But now that you just started finishing your second bats, the weather changes and – with it – the air pressure. The boiling points are off by (say) 0.3C. That is 0.3 C lower.
You make your cuts according to plan at 80, 95 and 98 degrees Celsius, but you should have cut at 79.7C, 94.7C, and 97.7C. You have just collected more heads than before, limiting the fruity flavors in your whiskey. And you hearts to tails cut was also 0.3 degrees late, resulting in more root-like and nutty flavors in your whiskey than usual.
Don’t make the mistake of thinking that 0.3 degrees is nothing. In terms of a big production still, you may well be smearing too much early tails into your hearts for like 20 minutes! In short?
Due to air pressure variance, you just screwed up your finishing run …
iStill’s innovation to help solve air pressure variance related problems
“How do we solve air pressure variance induced, sub-standard cutting?” became an iStill mission. The first generation iStills calculated the boiling point (and any variance from “standard”) by stabilizing the units, after heads were taken, for long enough to achieve the pure azeotropic ethanol boiling points near the take-off point of the column. We would then use that input to correct cuts.
The latest iStills are far more sophisticated. They are equipped with a sensor that monitors air pressure every second. Following the sensor’s input, the programming calculates any deviation from “standard” on a second-to-second basis. Thus giving your iStill perfect insight into boiling points that then automatically translate into perfect (corrected) cut points.
We call this feature “Dynamic Cuts Management” or DCM, and it is one of the reasons why iStills make better product more consistently than any other still out there. It now comes standard on all our units. It can be retrofitted on most of the existing NextGen units.
Air pressure sensor iStill style …