Using a microscope to monitor fermentations at Lapierre

Natural winemaking doesn’t mean just letting wine ferments do their own thing. If you want to make good natural wines, you need to pay attention.

Matthieu Lapierre

Yesterday I visited Domaine Marcel Lapierre, where Matthieu Lapierre showed me how he uses a microscope to monitor the course of fermentations. The goal at Lapierre is to make wine naturally, with no additions, but to do this well you have to be monitoring things. His father, Marcel, was the pioneer of natural winemaking in the Beaujolais, and he began looking at the fermentations under the microscope, after learning what to look for with the help of a microbiologists. The other natural-leaning Beaujolais producers also tend to do this, and Lapierre shares his microscope and know how (they have a microbiologist who assists to this day) with friends. As I was visiting, Alex Foillard was over checking out one of his ferments.

Matthieu points out the different microbes in the wine

Matthieu explained what he’s looking for. This is a critical stage of fermentation, as things are finishing off. The wines here are made with a version of carbonic maceration. The vats are filled with whole bunches, and under the weight of the grapes at the top, some juice is released which begins an alcoholic fermentation at the bottom of the vat, releasing carbon dioxide. The intact berries in the whole bunches above this begin an enzymatic transformation, releasing some colour from the skins which then stains the pulp. The enzymatic ‘fermentation’ results in the degradation of malic acid and some of the sugar, producing a little alcohol and also some flavour precursors. Then, after a period of a week or so the juice that has been released is drained off, the still-intact whole bunches are pressed, and the resulting juice goes back into the fat for an alcoholic fermentation. Before it reaches dryness, it then goes to barrel.

The microscope used

It’s this last stage of ferment that’s of most concern to natural winemakers. At this stage there have been no additions at all, and there is still a bit of sugar. Matthieu and his colleagues want to know what sort of microbes are present. They want the last bit of sugar to be eaten up by Saccharomyces cerevisiae, the main alcoholic yeast, and not bacteria.

A short film of Matthieu demonstrating the microscope

In this wine sample, Matthieu points out that there’s quite a bit of S. cerevisiae present, which is good. They are budding, so they are alive and healthy. But there are also quite a lot of bacteria, as single cells, as pairs, and as chains. If these eat up the sugar, then the volatile acidity will rise. And if there’s any brett there, they can have a feed too, with bad results.

So what would he do with a wine like this? First of all, he’d try chilling it down to about 14 C, which will allow the yeast to carry on, but which is a bit too cool for the bacteria to cause much trouble. And he would do some battonage, stirring up all the yeasts, alive and dead. If the sugar doesn’t start dropping, then he would consider adding some sulfur dioxide: enough to knock out the bacteria, but not enough to take out the yeasts. ‘It’s a race,’ he says, ‘and the horse that we want to see win is this one,’ pointing at S. cerevisiae on the screen

To do this sort of monitoring, you need a research-grade microscope with a magnification of around 800-1000 (good quality optics help, and this microscope had a x40 objective lens, with an eyepiece that I’m suspecting was x20; you can get x100 objective lenses, but these need to be oil immersion, where the end of the lens is in a drop of oil on top of the slide coverslip, and they are a bit of a pain to use). They aren’t crazy expensive, especially if a few vignerons pool their resources and share it. And it means you can have a much better chance of making sound natural wines.