A German great-grandmother called Maria Thun is wielding huge influence on the British wine industry. A calendar she first published in the 1950s categorises days as "fruit", "flower", "leaf" or "root", according to the Moon and stars. Wine is best on fruit days, followed by flower, leaf and root days. The worst day is marked as "unfavourable" in the calendar. (See factbox below for forthcoming "good" and "bad" days).
Tesco and Marks & Spencer are the latest supporters of her philosophy. The two supermarkets have revealed that they have a policy of inviting critics to taste their wine only on days which the calendar says are favourable.
Her theory is that wine is a living organism that responds to the Moon's rhythms in the same way that some people believe humans do. The so-called "lunar effect" has been widely dismissed as pseudo-science but its followers think that as the Moon exerts such a huge impact on the tides, it must follow that it affects the water in the human body and therefore human behaviour.
The belief that wine can taste different depending on the day it's drunk is not as eccentric as it may sound. All wine experts tend to agree - although their theories on why vary. Wine merchant David Motion has recently been won over to Maria Thun's "biodynamic" calendar theory.
"We tried eight wines on Tuesday, which was a leaf day and then the same wines again on Thursday, which was a fruit day. And it was totally conclusive. "It wasn't that the wine tasted bad on the Tuesday but it was much more expressive on the Thursday. It was more exuberant and on-song. It was like the heavens opened, the clouds parted and the wine just expressed itself."
The trial solved his long-standing puzzlement at why the same wine could taste so much better on certain days. From now on, he says, his wine shop in north London will only hold tasting sessions on fruit days. The biodynamic calendar is part of the wider concept of biodynamic farming, pioneered by Rudolf Steiner in the 1920s. The philosophy is similar to organic farming but a key difference is that planting and sowing is timed according to the moon.
Biodynamic farming has itself had an influence on the growing industry - with some wine growers running their vineyards along these lines. Despite its growing traction in viticulture there's still much scepticism in the trade, with some scientists dismissing it as sorcery.
The resident wine expert at London's Vinopolis, Tom Forrest, agrees it all sounds a "little bit like witchcraft". "But having thought about it and spoken to biodynamic wine producers, I'm more sure there is some sort of influence. Whether it's a huge influence or not, I don't know."
The Moon can impact on a plant through changing water levels, he says, so there is something to be said for the way it can influence wine. But Jamie Goode, a wine scientist and author of online magazine wineanorak, thinks too much is made of planetary alignments and the lunar calendar.
"But I'm not going to say it's absolute nonsense. Wine tastes different on different days but the differences are not that huge and the differences are more about atmospheric pressure. "And we are part of the equation when it comes to tasting wine. We are not measuring devices. The taste of the wine is something we generate in response to the wine."
People taste wine with expectations, and part of that could be the knowledge that it is a "good" day for wine, he says. Mood also influences There are other aspects of biodynamic farming that could explain why producers that switch to it from conventional methods tend to improve the quality of their wine, he says. And they have nothing to do with the Moon. They don't use pesticides, they compost, they till manually and they use other crops to create a more diverse eco-system.