Rotary evaporator: what it is and what it's used for | Giovanni Ceccarelli

Rotary evaporator: what it is and what it’s used for

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A rotary evaporator is a distillation device that has been been around now for some years in the kitchens of renowned restaurants and prestigious bars.

Many also call it rotOvapor, however the correct diction is rotAvapor. It should be noted that this term is a registered trademark by Büchi, therefore it should only be used to indicate evaporators produced by this company. Walter Büchi, founder of the company with the same name, invented it in 1957.

Let’s find out now what the rotary evaporator is and why some bars and restaurants have decided to buy this expensive tool.

As I’ve already written in the introduction to this article, the rotary evaporator is nothing more than a distiller. Yet what makes it different from the classic ones?

The particularity of this distiller is that it is designed to be connected to a vacuum pump. This pump draws air from inside the distillation circuit, reduces the pressure inside the system and, consequently, lowers the boiling temperature of the liquid to be treated.

In order to better understand this concept, consider how the temperature of boiling water varies: at sea level water boils at 100°C, while in high mountains, for example at 4,000 meters above sea level, it boils at 86°C. This is because at high altitudes the atmospheric pressure is lower.

The rotary evaporator can distill even at 20°C or less.

As you can imagine, this has countless advantages! Let’s have a look at them together.

First of all there are energy savings because the liquid doesn’t need to reach temperatures above 78°C as with common distillers. For limited use, such as a bar or a kitchen, energy saving is probably negligible, while other aspects are very important.

Reducing the boiling temperature allows for distillation at a low temperature. Distilling at a low temperature allows to preserve all those substances that are sensitive to this parameter.

In addition to lowering the pressure, drawing air from the system has another consequence: inside the circuit, the amount of oxygen is extremely low which implies a low oxidation of the product you’ll be treating!

So, to sum up, distilling in vacuum entails greater respect for all those substances that can be altered by oxidation or high temperatures.

Let’s now have a look at what the two main uses of this tool are in bars and kitchens.

Personally, I think that this tool is great to make cold reductions. A fresh fruit juice consists of water, sugars, acids and other substances, including aromatic ones. The rotary evaporator allows you to remove water from the juice by concentrating the juice and making it much more tasty.

Think of a Daiquiri made with lime juice concentrate, a Satan’s Whiskers made with concentrated orange juice or a Bloody Mary prepared with fresh tomato juice (from slow juicer) and then concentrated (it’s certainly not the tomato concentrate that is sold in tubes).

Cold reduction does not cause any product changes due to temperature! The juice will remain fresh, as if freshly squeezed, but with more flavour!

You can also make liquor reductions. One of the first reductions I made was of Campari. Reducing a liqueur is interesting because two products are obtained from this process: the reduced liqueur, which will have a lower or theoretically zero alcohol content, and the distillate of that liqueur. In fact, in this case, the liquid that evaporates is alcohol, while the distillate is obtained in the collecting flask. On the one hand the Campari reduction, on the other the Campari’s distillate.

And finally you can distill tinctures obtained from spices or aromatic herbs. After extracting in alcohol, for example mint, you can distill and obtain a transparent, mint flavorful distillate.

Lastly, let’s talk about risks.

This instrument doesn’t have any particular operational risks. Risks derive, as in most cases, from improper use of the instrument and raw materials. It is important to highlight that it is necessary to avoid distillates made from fermented liquid because they may contain methanol, which would be concentrated in the distillate.

Another article on the evaporator will follow; it will be a bit more technical and I will go into detail on how the instrument is built, its operating principle and its regulating parameters!

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Happy distilling,

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