Oenologie - Les techniques des vignerons pour lutter contre le gel - Les Grappes

Winegrowers' techniques to fight against frost

With the cold spells and spring frost, the vines are subject to very low temperatures. Spring frosts can go as low as -9°C. The vines risk losing their buds and the winegrowers risk losing production. Crops may be lost because of frost. So here are some tips to fight against frost on the vines, and hope to limit the damage.

Warming up the vines

In spring, when temperatures rise, the first leaves and buds appear. The buds can withstand temperatures down to -3°C, but beyond that, they risk freezing: the sap, rich in water, will freeze, and "burn" as the winemakers say the embryonic tissues of the flower or leaves.This is what causes the death of several parts of the plant.

If you cannot impose your law on nature, the aim here is to limit the damage. To fight against frost, the air around the vines must be warmed up. The idea is to prevent the temperature from dropping too much: and to do this, the winegrowers apply themselves to heating the air, or preventing the vines from cooling down further.

Candles and braziers

One of the widespread practices is the arrangement of candles. This method consists in arranging in the vineyard of large candles, blocks of paraffin in metal boxes. The wax of the candles is natural. Another trick is the constitution of braziers, placed in the middle of the vines. The candles and braziers will warm the air around the vines, and thus prevent the temperature from falling too much. Another trick is recommended here: you can also have heating fans to stir the air, and allow the heat to be distributed evenly. Frost is thus avoided.

The only problem with candles: there is only one company in France that produces them, it quickly finds itself out of stock.

The heaters

The use of heaters is also widespread: they are placed between the rows of vines and thus allow to gain up to 3°C. Like candles, they require a great deal of labour in the arrangement of the heaters.

The use of heaters offers a beautiful night show, but is not very environmentally friendly. Indeed this practice emits carbon dioxide.

Spraying

Sprinkling consists of sprinkling the vines with water. In this way the buds are caught in a pocket of ice without the water they contain freezing. This is called the phenomenon of undercooling. This is a delicate technique because the ice cube must not thaw too quickly. Thus it is necessary to water the plots until the temperature becomes positive again. The sprinkling is thus continuous.

This system is considered to be efficient but requires consequent installations: pipes and sprinklers are very expensive. This is why this system is often reserved for the most exposed plots.

Propane burners

It is more affordable, more automatable and less polluting. It involves the use of propane burners in the vineyard to heat the air, with 150 burners per hectare.

Wind turbines

They are used here as air brewers. Indeed, these small 11m high aeolian wind turbines, by stirring the air, will direct the air located above the vines towards the stocks. This air, a little warmer, then allows the vines to be warmed up.

The helicopters

Finally, some winegrowers use helicopters to mix the air. The helicopter flying at low altitude (i.e. below 20m) stirs and heats the air above the vile. The air at the level of the vine stocks is thus warmer, which prevents frost.

This operation remains dangerous, since it is carried out at dawn, therefore with little light. It is also expensive, since it is necessary to count 170euros per hectare. However it is a method that works and is profitable, since it could effectively protect a vineyard.

Marie Lecrosnier-Wittkowsky for Les Grappes

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