How native yeasts are captured. From vineyard swabs to a winemaker's own strains.

A winemaker who wants to keep his yeasts

The project starts with Loïc, a vigneron who believes the biodiversity of each parcel is worth protecting, from the plants and insects to the microscopic life. He asked a team of scientists to help him understand the yeasts living in his vineyards and to preserve them for the future.

Loïc explains why. He wants to work with yeasts that have lived alongside his grapes for years and carry the message of his terroir. Industrial yeast, he says, is very strong and can push out the other yeasts that add complexity. He has even placed his yeasts at the Institut Pasteur in Paris for 30 years, so that the next generation can still use them if climate change makes them disappear.

Sampling in the vineyard and the cellar

The fieldwork is a pleasure to watch. Using sterile swabs, the team collects yeast from grapes, plants and other surfaces inside the parcel and around it, because yeasts are carried in by insects, animals, wind and rain. The samples go into sterile media rich in sugars and amino acids, with natural antibiotics to stop bacteria from growing.

They also sample the cellar: old wooden equipment, amphoras and walls. Old wood absorbs moisture and microbes from the cellar air and acts like an incubator, a technique the scientist Davide brought over from earlier work with breweries. Not every yeast found will be welcome; one taken from an amphora or a wall might cause problems, so the aim is to screen everything first and then choose. A chemist who is also a sommelier joins the fieldwork so she can link later results back to each sampling spot.

Isolating and naming each yeast

Back in the lab, the first step is isolation. Samples are diluted and spread on plates so each yeast grows into its own colony. Colonies are picked and replated two or three times until every strain is separated. Yeasts are single cells that divide every 20 to 60 minutes, so they multiply quickly in the incubator, where microbiologists check them every day.

Next comes identification. The team studies each colony's shape and, under the microscope, confirms that it is a healthy yeast. Then molecular biology, analyzing DNA or proteins against international databases, gives each strain a name.

Testing what each strain can do

Each yeast is then tested. Can it ferment sugars such as glucose and fructose, producing CO2? How much ethanol does it make? The team uses the winemaker's classic method of tracking density as well as lab instruments that measure alcohol and other compounds precisely.

Not every useful yeast makes much alcohol. Some contribute aromas through enzymes that release flavor compounds bound to sugars, a process called deglycosylation. Others produce faults such as acetic acid. The final report tells Loïc which strains do what, so he can choose his own blend, and the lab can grow exactly the quantity he needs.

Science with humility

The film ends on a thoughtful note. The scientists admit how much about wine they still cannot measure and why they need winemakers and sommeliers alongside them. The lead scientist calls the goal a controlled spontaneous fermentation: indigenous yeasts, but with less risk of off-flavors. Loïc compares it to grape varieties. You can make wine with just one, but more varieties bring more complexity, and the same is true of yeasts.

Hear why one of them calls wine a time machine, and see how this work could make spontaneous fermentation less of a gamble.