Tickling those taste buds: Rotary evaporation for flavour creation

Bart cooks up a real tasty post by presenting the use of rotary evaporation for finding exciting new flavours in bars and molecular kitchens. Learn the basics of the technique, the components of a rotary evaporator, what aromatic compounds are extracted for flavour creation for mixologists and chefs and see two examples of recipes using rotary evaporation in his latest post.

My last post might have been about a cool bartender but let me tell you about an amazing dining experience I had to celebrate the beginning of my retirement. My daughter treated me wife and me to a dinner in a molecular gastronomy restaurant! My goodness, I wish I could describe the appearance and taste of the food we tried that evening. Imagine anything from transparent pasta to fruit caviar and powdered Nutella for dessert. Imagine my surprise and satisfaction when I was offered a special visit to the molecular kitchen and there in the midst of it all was a rotary evaporator for the preparation of distillates and extracts.

Now the gastronomical applications of rotary evaporation are either to concentrate flavors or to extract volatile aromas or flavours from mixtures without unnecessary heating. It is not just molecular kitchens that use rotary evaporators to preserve and play with each flavour. Mixologists and bartenders are increasingly investing in the equipment to create fantastic drinks for their clientele.

And since I know a thing or two about rotary evaporation, I decided I’d like to write a rotary evaporation post dedicated to mixologists and molecular chefs.

I guess I will begin at the beginning in case some of you are beginners with this topic.

How can you use rotary evaporation for flavour extraction?

In the simplest of terms, you place your sample in a flask and you heat the sample in a system that is under vacuum. Why do you need the vacuum, you may be wondering? The vacuum decreases the boiling point of your solvent or your sample, so that it can boil at lower temperature than what would be necessary at normal air pressure. You do not need to add as much heat as you would need to add under ambient conditions, so your treat your sample more gently.

By avoiding high temperatures, you manage to keep the flavour in your sample intact.

As the sample is heated, vapour escapes and enters the condenser. The condenser is cooled by water or by a re-circulating chiller. The condenser is where energy is removed from the reaction and as the vapour cools, it forms a condensate which collects in a separate receiving flask.

Now, scientists are typically interested in the remaining residue after solvent evaporation, whereas those looking to create flavours for molecular gastronomy and mixology applications are often concerned with the distillate itself.

Let us explore the rotary evaporation system components in a bit more detail. In order to have a well-functioning unit, you require:

  • A vacuum pump which generates the vacuum needed for flavour preservation
  • A chiller which contains ethylene glycol and eliminates the use of water in the condenser. The circulating ethylene glycol in the condenser not only reduces water consumption, it also results in more consistent temperature maintenance than in cases where water is used instead.
  • Interface , which offers the user the ability to set-up and control all parameters of the rotary evaporator, including vacuum, rotation speed, heating bath, chiller and vapor temperature as well as lift status. If you are setting up your method with the interface, pay attention to the heating bath and chiller temperatures. I would recommend keeping these values always the same to ensure the consistency of your process. For example, heating bath at 50°C and chiller at 10°C would almost certainly provide you with good results. With a good interface, you should be able to set the vacuum automatically using a feature such as a solvent library. There, you can select either ethanol or water as your solvent, depending on the sample from which you are extracting a flavour from. The vacuum should be then set automatically depending on your solvent.
rotary evaporator, rotavapor, rotary evaporation system

And to really perfect your rotary evaporation for flavour creation, I would suggest using two accessories:

  • Beaker flask with a larger opening than a normal evaporating flask in order to easily add and remove sample
  • Foam sensor, especially when handling natural products, which tend to foam. The foam sensor reaches into the beaker flask and automatically aerates the system whenever foam forms. By automatically breaking the vacuum, foam formation is prevented. If you ignore the foam, the foam will eventually spread sample all over the glassware of the rotary evaporator and enter the condenser. At this point, you will have to clean the entire system, a task that is certainly tedious and better left avoided.
rotary evaporation, mixologists, bars, distilleries, gin

So what exactly are you extracting to obtain a flavour when you use a rotary evaporator ? There are many examples of aromatic compounds that influence the final taste of your product, such as:

  • Esters – formed during alcoholic fermentation via yeast metabolism, these aromatic compounds are the main class of flavour compounds in distillates. Specific examples include ethyl acetate (fruit), phenylethyl acetate (flower), benzaldehyde (almond), ethyl lactate (butter-dairy-malolactic fermentation)
  • Terpenes – primary constituents of essential oils and many types of plants and flowers. Essential oils are widely used as fragrances in perfumery and traditional medicine; these produce limonene (orange) and nerol (sweet rose) odours
  • Alcohols – for aroma; examples include benzyl alcohol (almond), ethyl maltol (cooked fruit), furaneol (strawberry), menthol (peppermint), etc.
  • Aldehydes – such as acetaldehyde (pungent), benzaldehyde (marzipan, almond), hexanal (green, grassy), cinnamaldehyde (cinnamon, citral (lemongrass, lemon oil), hexenal (green tomatoes), neral (citrus, lemongrass), vanillin (vanilla).
  • Amines – such as cadaverine (rotting flesh), Indole (jasmine flowery), putrescine (rotting flesh), pyridine (very unpleasant), trimethylamine (fish)
  • Ketones – such as octenone for a blood, metallic, mushroom-like aroma effect, acetyl pyrroline for bread and jasmine odour, and acetyl tetrahydropyridine for fresh bread, popcorn odor.
  • Lactones – for a sweet coconut odour

Now that we’ve explored a bit about the method and the theory behind flavour creation with rotary evaporation, I’d like to offer you two recipes from the Jerry Thomas Project on how to use the technique to create innovative new products.

For a mixology application, you can use rotary evaporation for an exciting new flavour take on Bourbon: Set your rotary evaporator as follows:

Thermal bath: 52 °C
Chiller: 5 °C
Vacuum: 80 mbar

Then pour 1.308 g of bourbon whiskey into an evaporation flask. Evaporate the solution for 40 minutes at 80 mbar. Lower the pressure to 60 mbar and evaporate the solution for 10 minutes. Lower the pressure to 55 mbar and continue the distillation process until a solution with an alcoholic strength of 72 abv is obtained. Stabilize the solution with demineralized water until an ethanol content of 45% is obtained. Store in an airtight container for 24 hours before use.

For a molecular gastronomy application, to create a mole sauce that bursts with unexpected flavour set your rotary evaporator parameters as follows:

Thermal bath: 45 °C
Chiller: 5 °C
Vacuum: 80 mbar

Then pour 10 g of mole sauce and 100 g neutral grain spirit with an ethanol concentration of 50% in the evaporation flask. Evaporate the solution for 40 minutes at 80 mbar. Lower the pressure to 70 mbar and evaporate the solution for 10 minutes. Lower the pressure to 60 mbar and evaporate the solution for 15 minutes. Lower the pressure to 50 mbar and continue the distillation process until all the solution has completely evaporated. Stabilize the solution with demineralized water until an ethanol content of 50% is obtained. Store in an airtight container for 24 hours before use.

Now I’ve just begun to give you a taste of using rotary evaporation for flavour applications in mixology and molecular gastronomy. To get more of a complete meal, check out a webinar on the topic of flavour creation or gain continuous access to distillation resources via Instagram .

How did you like this application-specific post? Would you like to learn more about this or another application of rotary evaporation? Leave me a comment below with your requests. Until then, Bon Appétit!

Till next time,

The Signature of Bart Denoulet at Bart's Blog