Fire and Ice

Oct 23, 2020

Captivating pictures aren’t they? In fact quite pretty – until you realise what is going on here.

Across France, farmers are counting the cost after three nights of sub-zero temperatures in April (their Spring season)

Temperatures dipped to record lows such as -8’c in some areas, and farmers tried every method they could to save their crops. 

But for many winemakers, the 2021 harvest is ruined. The French Minister of Agriculture said he would declare an agricultural disaster, with losses heading for the Billions of euros.

Some of the worst frosts in recent history, settled across almost all of the major wine-making regions in France, which have consistently produced some of the finest wines in the world for literally centuries.

Upon closer inspection, the rows of colourful lights are actually small fires – usually a big candle or a tin full of paraffin with a wick in it. But what exactly are they doing with all these candles…?

The spring frosts have been a feature in France for the longest time, but have generally landed in around the +1’c to -1’c range, which is not quite cold enough to cause lasting damage to the soft and newly appearing fruit buds.

However, over the last 2-3 years, getting progressively worse, these temperatures are now hitting -4’c or -6’c, the lowest this year being recorded at -8’c – and this is lethal for the plants and crops – so various means are used to try and head the frost off before it settles.

Lighting all the candles creates two effects: it raises the temperature, hopefully, enough to get back out of the lethal range, but also creates swirling air movements which force the sinking colder air (frost) back up into the warmer inversion layers above them.

So back to the candles – They are generally effective when the farmer places 300-400 such candles (or bougies as they are also known as) per hectare – each one will last one night before needing to be replaced – and at an approximate cost of €10 each, you can do the math to work out the financial impact here. But of course what are the options? Lose the entire crop and vintage for the year or spend hard-earned money on this? Hardly a great choice. 

Despite the valiant efforts, it seems that much of the 2021-22 French harvest was lost since the sustained 3-4 nights of these temperatures was just too much to fight. Truly devastating.

If one drives through the Huguenot tunnel towards Worcester, one soon arrives at the turn-off to Rawsonville on the right – and from that very point onwards, if one looks closely, one will see stacks of old vines and hay bales at certain points in the vineyards – this is our SA version of how to deal with the rogue frosts that sometimes land in the Breedekloof valley. There are still other means as we will see now.

As odd as it may seem, another method to try and stave off Jack Frost is to use well calculated and well-timed irrigation. In other words, spray the vineyards with water!

As counter-intuitive as this seems, it works in two simple ways: primarily, the creation of ice on the plants is a different type of ice from frost – put simplistically it is a ‘smooth’ ice, whereas frost is a set of ‘jagged’ ice crystals that rip and tear plant material, so the smooth ice is less harmful. Secondly, the covering of ice from irrigating gives off latent heat that is actually sufficient to prevent the tissues within the plant from themselves freezing.

The following morning, the vineyards then typically set light to the hay bales and this creates a smokescreen that prevents the morning sun from burning the tender shoots and buds through the ice, but rather lets it melt slowly as the day warms up enough.

Other methods used (and in some cases, all of these are employed at the same time) giant fans are employed to shift the sinking cold air back upwards and even the use of helicopters that (by virtue of their means of staying in the air), suck the warmer inversion layers downwards to displace the sinking cold frosts. Whichever one or several you choose, it’s a tough and extremely expensive fight.


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