Anyone dealing with the topic of flavor management will repeatedly come across terms that are rather unfamiliar to everyday life in both bar and kitchen. It is now well known by now, that the whole process has something to do with a rotary evaporator. But what about foam brakes, boiling points and hydrosols? The purpose of this article is to give a first overview of the most important wording - so you may have an overview and be able to form your own opinion.
We can' t do it without it: The rotary evaporator, also often simply known as Roti, is the device that has managed to break through from its primary area of use, the laboratory and conquer the world of kitchens, bars and microdistilleries. Why? We have explained that for you in this blog post. Briefly: The device enables, among other things, the so-called cold distillation to gently extract flavors that would be lost in other processes due to excessively high temperatures.
This is done by placing the herbs, fruits, vegetables or other ingredients whose flavors are to be extracted in a so-called evaporation flask or rotating flask together with spirit or water. This is a pear-shaped or round glass bubble with a finely cut opening. These flasks come in a wide range of sizes, varying from 10 ml capacity up to 100 L for industrial evaporators However, in the area of flavor management, 1 to 2 L flasks are typically being used.
The filled flask is pushed with the cut opening over the corresponding counterpart on the rotary evaporator and fixed there: the so-called vapor tube, also called steam guide tube. Subsequently, the steam produced can rise through this small glass tube. If you are working with ingredients that tend to foam during the process (milk or teas are such candidates), it is recommended to place a so-called foam brake between the vapor tube and the evaporation flask. This glass part is composed of a small glass sphere with two sections into which a tap has been fused, and serves the purpose of ensuring that the foam created reaches the sphere via the curved device, expanding there and thus collapsing instead of shooting through the vapor tube and contaminating the distillation area.
First of all, the flask with the ingredients must be slightly warmed up before anything happens in the device. The normal temperature is 40 to 50 °C. This is done by lowering it via the lift of the rotary evaporator into the heating bath filled with water. To distribute the heat evenly and ensure that the process later functions efficiently, the flask is set in rotation by a motor This can be programmed into the device using the unit "rpm" = rounds per minute. The selected speed will depend on the size and filling capacity of the flask.
Another parameter that must be set is the vacuum. The negative pressure generated by a vacuum pump in the rotary evaporator is the only way to ensure gentle aroma processing at low temperatures. The pump pulls the air from the glass body of the device, making it easier to evaporate the alcohol, water and the so-called volatile flavors. This operates on the basis of a basic principle of physics: The lower the pressure goes, the lower the temperature is at which a fluid starts to boil. This temperature is the so-called boiling point. For water, this is normally 100 °C - but under vacuum it can be lowered, e.g. to 50 °C. How exactly this all works is described in more detail in this blog post.
The resulting steam now rises from the evaporation flask via the vapor tube into the condenser. In this case, it is a hollow glass cylinder, which has several glass tubes inside, twisted together. The coolant - either tap water or, better still, the coolant of a recirculation chiller - flows through this. This pumps the liquid constantly in a circuit and cools it down again, so no water is wasted. Due to the cold, 5 °C being normal, the vapor condenses on the glass tubes to form a liquid. The steam contracts. Drops are formed which, under the force of gravity, fall down into another glass bubble: the receiving flask. It also has a cut opening, in the so-called spherical cut, that is flexible like a joint. The receiver flask is attached to the condenser with a metal clip and the result of the process is collected in it: If a spirit was utilized, it is referred to as a re-distillate. In case water was used, the product enriched with the aromas is known as a hydrosol. In some instances, you may also be interested in what remains in the evaporating flask, e.g., when thickening sauces or juices by gently distilling out the water. This result is called concentrate or reduction - in the same way as the well-known reductions from cooking, where the water content has been reduced by boiling.
Do you still have any open questions? Are you still missing the clarification of a term? What should we write about next time? Let us know by leaving a comment on this article. We are looking forward to receiving your feedback!
Your Heidolph Team
Pictures: ©Weisshorn Spirits Sarl, Matt the List