Lunar Calendar (Maria Thun)

If you have ever heard a sommelier say “today is a fruit day, the wine will show better,” they are using the Maria Thun lunar calendar. It is the most public face of biodynamics in restaurants and trade tastings, and the part of the system that produces the strangest-sounding claims for a casual drinker.

What Maria Thun built

Maria Thun was a German farmer and student of Steiner who spent decades running comparative trials in her own gardens from the 1950s onward. She concluded that the moon’s position against the twelve zodiac constellations, the sidereal position, correlated with plant behaviour. Each constellation, she argued, governs one of the four classical elements, and therefore one part of the plant: earth for root, water for leaf, air for flower, fire for fruit.

From that framework she built a yearly calendar. Every day is classified as a root day, leaf day, flower day, or fruit day. Vineyard work is timed accordingly. Pruning is done on root or fruit days. Bottling and racking are scheduled to avoid leaf days. And, most visibly to consumers, wine is meant to taste better on fruit days.

Her son Matthias has continued the calendar since her death in 2012. The current English edition is published by Floris Books in Edinburgh, which makes it the most widely read biodynamic reference in the UK trade.

The M&S experiment

The most-cited English-language test ran in 2009. Marks and Spencer’s wine team, working with a panel of trade buyers and Decanter editors, opened the same wines on consecutive days that the Thun calendar classified as fruit, root, leaf, and flower. The panel was not told which day was which. They consistently rated fruit-day samples more open and expressive, and leaf-day samples flat. The result was widely reported and just as widely qualified, because the trial was not blinded to brand and was not statistically powered.

Tesco’s wine buyers have run their own internal version. Several Master of Wine students have used variations on it for dissertation work. The pattern shows up often enough to be interesting and not often enough to be conclusive.

What the science says

There is no plausible physical mechanism by which the sidereal position of the moon changes a wine in the glass. Atmospheric pressure on a given day matters more for how a wine smells than any cosmic signal could. Jancis Robinson has argued that the calendar effect is a real perceptual phenomenon, but probably driven by humidity, temperature, and the taster’s own state rather than by the moon.

Producers who use the calendar tend not to argue against this. Their position is pragmatic. The calendar is a scheduling tool that imposes rhythm on the year. If it also happens to nudge a tasting in the right direction, that is a bonus, not the point.

How to use it as a drinker

Open a serious bottle on a fruit day if you have the choice. Avoid leaf days for important tastings. Do not arrange your life around it. The calendar is one variable in a glass that already contains many: bottle variation, serving temperature, glassware, what you ate two hours ago. Track your own observations over a year and decide whether the pattern holds for you.