A hot summer is not necessarily a bad summer for the vine. Quite the opposite: Chardonnay needs sunshine and warmth to build its ripeness. The question is therefore not whether the vine likes heat, but at what threshold heatwaves and drought stop nourishing it and begin to constrain it.

That limit is one we observe ever more closely each year in our southern Burgundy slopes. It cannot be read from a thermometer alone, but from the behaviour of the plant: the colour of the foliage, the firmness of the berries, the speed at which a parcel feels the strain depending on the depth of its soil. Here is what heat really changes in the grape, in yields and, ultimately, in the wine.

How does the vine react to a heatwave?

The vine is Mediterranean in origin and remarkably resilient. It has a simple, effective defence mechanism: when the strain becomes too great, it closes its stomata, those tiny openings on the underside of the leaves through which water vapour escapes. By closing them, it limits its water loss and protects itself.

But that protection comes at a price. Stomata also serve to absorb the carbon dioxide needed for photosynthesis. A vine sheltering from the heat partly stops manufacturing the sugars destined for its grapes. Ripening slows, sometimes to a halt: this is what we call a ripening block.

Therein lies the paradox. Moderate heat accelerates ripening; extreme heat holds it back. Between the two lies the zone where the vine works at its best, and it is precisely that zone we seek to preserve through our summer work.

Drought and grapes: smaller berries, shifted balances

Drought acts first on berry size. The grape is largely made of water; when water runs short, the berries stay small. The ratio between skin and pulp is thereby altered, in favour of the skin.

This is not necessarily a fault. The skin holds a great part of the aromas and the substance. Moderately constrained berries often give denser, more expressive wines. It is the basis of the widely held idea that mild water stress can serve quality.

The important word is mild. Beyond a certain threshold, the constraint ceases to be beneficial: photosynthesis stops, aromas no longer build, and the grape dehydrates instead of ripening. The result is juice rich in sugar but poor in flavour, giving unbalanced wines, warm on the palate and without length.

Heat also acts directly on acidity. Malic acid, one of the grape's two principal acids, is consumed by the plant all the faster as temperatures rise, particularly at night. This is why night-time coolness often matters more than the afternoon peak: it is during the night that white wines keep — or lose — their nerve.

A fine hot year is recognised less by its days than by its nights. It is at night that the grape preserves — or loses — the freshness that will give the wine its drive.

What effect on yields?

Heat and water shortage weigh on the volume harvested, along several paths that can compound one another.

  • Smaller berries: for an equal number of bunches, a reduced berry mechanically lowers the weight of the crop.
  • Sunburn: during an intense episode, over-exposed bunches can be scorched by the sun; the affected berries shrivel and cannot be picked.
  • Dehydration: late in the cycle, a grape that loses its water loses volume, even as it gains apparent concentration.
  • The delayed effect: a vine severely constrained one year builds fewer reserves and may produce a more modest crop the next.

On the scale of an estate, these effects are never evenly spread. A parcel planted on deep clay-limestone soil holds a water reserve that lets it weather a dry spell without faltering. A vine set on thin, stony soil will react far more quickly. This is one of the reasons we think parcel by parcel rather than across the vineyard as a whole.

The limestone of Solutré, a quiet ally

Our vines grow on clay-limestone soils, at the foot of the Rock of Solutré. This geology plays a real role in hot summers. Clay retains water and releases it slowly; fissured limestone allows the roots to descend in search of moisture deep down, well below the surface layer that dries first.

The age of the vines also comes into play. A sixty- or eighty-year-old vine has deep roots, built over decades. It draws on a greater volume of soil and comes through dry spells with more consistency than a young vine whose roots stay close to the surface. It is one of the least visible virtues of old parcels, and one of the most precious in a hot year.

How do we support the vine during intense heat?

Faced with a heatwave, the essential work consists in not adding constraint to constraint. Our interventions seek balance rather than performance.

Canopy management comes first. Trimming too severely deprives the vine of the leaf surface it needs to ripen its grapes. We prefer to keep a sufficient canopy, airy but full, able to shade the bunches during the hottest hours. Leaf removal is practised with measure: fully exposing a bunch on the setting-sun side amounts to exposing it to burns.

Soil work follows the same logic. Keeping a cover crop between the rows protects the soil from evaporation and preserves its microbial life, but that cover also consumes water. The trade-off is made according to the parcel, its water reserve and the year. There is no universal rule, only choices suited to each situation, in keeping with the approach we describe in our vineyard guides.

Heat and wine quality: the real stake

The final question is not volume, but balance. A successful white Burgundy rests on a tension between substance and freshness. Heat naturally pushes towards substance; it is therefore freshness that must be defended.

That is played out in the vineyard, through canopy management and the choice of picking date. It is also played out in the cellar: bringing in cool grapes, avoiding oxidation, working gently. A hot vintage well handled does not give a heavy wine. It gives a more sunlit, ampler wine that keeps its line — as we seek to achieve in each of the estate's cuvées.

Does drought inevitably damage the vintage?

No, and it matters to say so. A moderate drought can even concentrate the grapes and give wines of fine density, provided the vine never tips into a ripening block. What makes the difference is not the intensity of the summer, but the terroir's capacity to buffer extremes and the soundness of the decisions taken week after week.