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

Winegrowers' techniques to fight against frost

With cold spells and spring frosts, the vines are subject to very low temperatures. Spring frosts can go down to -9°C. The vines risk losing their buds and the wine growers risk losing production. Harvests can be lost because of frost. Here are some tips to fight against frost in 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 up to -3°C, but beyond that, they risk freezing: the sap, rich in water, will freeze, and "burn" as the winegrowers say the embryonic tissues of the flower or the leaves.This is what causes the death of several parts of the plant.

If we cannot impose our law on nature, we must 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 for that the winegrowers apply themselves to warm the air, or prevent the vines from cooling down more.

Candles and braziers

One of the widespread practices is the arrangement of candles. This method consists of placing large candles, blocks of kerosene in metal boxes, in the vineyard. The wax of the candles is natural. Another trick is to set up braziers in the middle of the vineyard. The candles and braziers will warm up the air around the vines and prevent the temperature from dropping too much. Another tip is recommended here: you can also place heated fans to stir the air, and allow the heat to be distributed evenly. This prevents freezing.

The only problem with candles is that there is only one company in France that produces them, and they are quickly out of stock.

The heaters

The use of heaters is also widespread: they are placed between the rows of vines and allow to gain up to 3°C. The company, like the candles, requires a great deal of labor in the arrangement of the heaters.

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

Sprinkling

Sprinkling consists in spraying the vines with water. This way, the buds are caught in an ice pack without the water in them freezing. This is called the phenomenon of supercooling. This technique is delicate, because the ice cube must not thaw too quickly. Thus, it is necessary to water the plots until the temperature becomes positive again. The spraying is therefore continuous.

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

Propane burners

This method is more affordable, more automated and less polluting. It consists of using propane burners in the vineyard so that they heat the air. 150 burners are needed per hectare.

Wind turbines

They are used here as air blowers. Indeed, these small windmills of 11m high, by stirring the air, will direct the air located above the vines towards the stocks. This air, a little bit warmer, allows to warm up the vines.

Helicopters

Finally, some wine growers use helicopters to stir the air. The helicopter flying at low altitude (i.e. below 20m) stirs and warms the air above the vineyard. The air at the level of the vines is thus warmer, which prevents frost.

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

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