Wine · Grape Growing · Study guide
Heat & Temperature
A study guide to warmth in the vineyard — why temperature decides what grows where, the factors (latitude, altitude, currents, aspect, diurnal range) that shift a site hotter or cooler, and the hazards of frost and heat.
Temperature is the master switch of the vineyard. A vine needs warmth to grow at all, and how much warmth a place gets decides what can ripen there — Riesling in the cool north, Grenache in the baking south, and nothing much beyond the temperate bands where wine is possible. But latitude is only the opening number: a stack of local factors — altitude, the sea, currents, fog, the slope's angle, even the colour of the stones — can push any given site warmer or cooler than its place on the map would suggest.
The framing idea: latitude sets the baseline; everything else is a modifier that moves a site up or down the thermometer. Learn the handful of levers, and you can explain why a vineyard at 33°S grows crisp, cool-climate wine, or why one at 50°N ripens at all. And because heat drives sugar up and acid down, every one of these factors is really a decision about the balance in the glass. (This is part of the Grape Growing library — the growing-environment cluster; the formal climate classification and its map are the next page, climate & weather.)
The one thing to fix first: vines need warmth, but latitude is just the start
A vine only grows when the temperature is above about 10°C, and it needs a whole growing season of sufficient warmth to ripen fruit — which is why most wine is made in two temperate bands, roughly 30–50° latitude north and south. But two vineyards on the same latitude can be worlds apart in temperature, because local factors override the baseline. Fix that idea — latitude proposes, geography disposes — and the rest of this page is just the list of factors.
The factors that change the heat
The memorise-cold table — each factor, which way it pushes, and where to see it:
| Factor | Effect on heat | Worked example |
|---|---|---|
| Latitude | The baseline: nearer the poles = cooler season (but longer summer days) | The 30–50° bands, both hemispheres |
| Altitude | Higher = cooler — about 0.6°C per 100 m — letting hot latitudes make wine | Mendoza's high desert; upland Spain |
| Ocean currents | Cold currents chill a coast; warm ones heat (and wet) it | Cold Benguela (South Africa) & Humboldt (Chile); warm Gulf Stream (NW Europe) |
| Fog | Cool sea air rolls into a hot region at night, dropping temperatures | Casablanca (Chile), Napa/Carneros (California) |
| Aspect | Slope direction: sun-facing slopes catch more heat | South-facing in the cool north (e.g. the Mosel) |
| Continentality | Big seasonal swing (continental) vs moderated (maritime) | Continental interiors vs the mild Atlantic edge |
| Diurnal range | Cool nights preserve acidity and aroma | Ribera del Duero's cold nights (Spain) |
| Water bodies | Seas, lakes, rivers warm and cool slowly, moderating extremes | Lakes and rivers buffering frost and heat |
| Soil | Dark stones absorb and radiate heat; clay stays cool | Priorat slate, Mosel slate, Rhône galets |
| Cloud cover | Reduces incoming heat and buffers day–night swings | Cloudier sites ripen more slowly |
Key facts
| Vine growth threshold | Roughly above 10°C |
| The wine bands | About 30–50° latitude, north and south |
| Altitude lapse rate | ~0.6°C cooler per 100 m of elevation |
| Cold currents | Benguela (S. Africa), Humboldt (Chile) — cool the coast |
| Heat in the glass | More heat → more sugar (alcohol), less acid, riper/fuller style |
| The night lever | Diurnal range — cool nights keep acidity and aromatics |
| Danger zone | Winter freeze below ~−20°C; heat stress above ~35°C |
The vocabulary you'll actually meet
- Cool / moderate / warm / hot climate — the growing-season temperature bands (Mosel is cool; Bordeaux moderate; southern France warm; Jerez hot). The formal version is on the climate & weather page.
- Continental vs maritime — continental = big difference between hottest and coldest months; maritime = small, moderated by the sea.
- Diurnal range — the gap between day and night temperature.
- Growing season — roughly April–October (N) / October–April (S); its average temperature is the number that matters most.
In this guide
- The factors in depth — the big geography, the moderators, and the ground
- The heat → grape → glass table
- Heat hazards: winter freeze, spring frost and its defences, and heat stress
- Around the world: Riesling vs Grenache, and the cooling tricks
- Classic exam questions
The big geography: latitude, altitude, currents, fog
- Latitude sets the starting temperature and the length of the season. Nearer the poles the growing season is cooler but summer days are longer, which helps ripening at the margins.
- Altitude cools a site by roughly 0.6°C for every 100 m you climb — which is why wine exists in otherwise-too-hot latitudes: Argentina's Mendoza sits high against the Andes, and upland Spain uses height to keep fruit fresh. Height also usually widens the diurnal range (below).
- Ocean currents can overrule latitude entirely. A cold current running up a coast chills the air above it: the Benguela off South Africa (Walker Bay, cool enough for Pinot Noir) and the Humboldt off Chile (Casablanca's balanced Sauvignon Blanc) both make coastlines far cooler than their latitude. A warm current like the Gulf Stream does the opposite — keeping north-west Europe mild and damp.
- Fog is the current's quiet partner: cool sea air drifts inland overnight into a hot valley, dropping temperatures and locking in fresh acidity. It's the secret of Casablanca in Chile and of Carneros/Napa in California.
The moderators: continentality, water, diurnal range, cloud
- Continentality measures the swing between the hottest and coldest months. High continentality (deep interiors) means short, hot summers and cold winters — a compressed, intense growing season. Low continentality (near the sea) means milder, gentler seasons.
- Water bodies — seas, lakes and rivers — heat and cool more slowly than land, so they moderate: warming in autumn/winter and cooling in summer, and buffering both frost and heat. Rivers can hold and reflect enough warmth to matter on a marginal site.
- Diurnal range is one of the most useful levers of all. Cold nights slow the vine's respiration, so the grapes hold on to acidity and aromatics even as they ripen by day — the reason high, continental Ribera del Duero (in Castilla y León, Spain) keeps such fresh, firm fruit despite hot afternoons, often keeping fresher acidity than warmer, lower-altitude Rioja. Warm nights, by contrast, push ripening faster and can cost freshness.
- Cloud cover simply reduces the heat and light a site receives and softens the day–night swing — cloudier regions ripen later and more gently.
The ground: soil heat and aspect
- Soil changes the temperature right around the fruit. Dark stones — the slate of the Mosel and Priorat, the galets (large pebbles) of the southern Rhône — absorb heat by day and radiate it back at night, effectively warming a cool site. Pale, water-holding clay stays cooler, taking more of the sun's energy to warm up.
- Aspect — the direction a slope faces — decides how much sun it catches. In the cool northern hemisphere, south-facing slopes are warmest and can be the difference between ripe and unripe (the Mosel's steep south banks); east and south-east faces get gentler morning sun (much of Burgundy's Pinot Noir), while south-west faces catch the warm evening sun.
Heat → grape → glass
| Condition | Effect on the grape | Effect in the glass |
|---|---|---|
| Warmer site | More sugar, less acid, riper flavours | Higher alcohol, fuller body, riper/jammier fruit |
| Cooler site | Slower ripening, higher acid, lower sugar | Lighter body, lower alcohol, crisp, fresher fruit |
| Wide diurnal range | Ripeness with retained acidity and aroma | Balance — ripe fruit that still tastes fresh |
| Heat-radiating stones | Extra warmth around the fruit | Riper fruit on an otherwise cool site |
| Excess heat (>~35°C) | Photosynthesis stalls; sugar-making pauses | Stalled ripeness, sometimes cooked/baked flavours |
Heat hazards
Warmth is life, but too little or too much is dangerous — and both extremes have defences:
Winter freeze. Deep cold below about −20°C can kill dormant buds, and in severe cases the whole vine. The graft (the join near the ground) is the most vulnerable point, so in cold regions growers "earth up" — mounding soil over the graft to insulate it through winter.
Too mild a winter is its own problem: without real cold the vine may fail to go properly dormant, leading to uneven growth, sometimes more than one crop (of lower quality), a shortened vine lifespan, and more surviving pests the frost would have killed.
Spring frost strikes at the worst moment — just as tender buds and shoots emerge — and can wipe out a crop. The classic defences:
- Heaters (bougies/chaufferets — candles and burners) warming the air between the rows.
- Wind machines that mix warmer air down onto the vines and stop cold air settling.
- Sprinklers (aspersion): spraying water onto the buds so that, as it freezes, it releases latent heat and holds the bud at 0°C — a coat of ice that paradoxically protects.
- Site selection: cold air sinks, so pooling in valley floors makes frost pockets — planting on slopes lets the cold drain away below the vines.
Growing-season extremes. Too much cold at flowering disrupts fruit set and shrinks the yield; too much heat does the opposite harm — above roughly 35°C the vine effectively shuts down, pausing photosynthesis and sugar production to protect itself, so ripening stalls in a heatwave.
Around the world: Riesling vs Grenache, and the cooling tricks
- The grape tells the climate. Riesling is a cool-climate grape — it ripens slowly and keeps its acid in marginal northern sites like the Mosel (~50°N). Grenache is the opposite: it needs sustained heat to ripen its big sugars, thriving in the warm southern Rhône and southern France. Name the grape and you've half-named the climate.
- Height for freshness. Argentina's Mendoza and high-elevation Spain use altitude to grow fresh wine at hot latitudes.
- Currents and fog for coolness. Chile's Casablanca and South Africa's Walker Bay ride cold currents and sea fog; so do California's coastal AVAs.
- Stones for warmth. Priorat's slate and the Rhône's galets radiate stored heat to ripen fruit on cool or windy sites.
Classic exam questions
- What's the minimum temperature for vine growth, and where is wine grown? — Roughly above 10°C; mostly in the 30–50° latitude bands, both hemispheres.
- How does altitude affect temperature? — It cools a site by about 0.6°C per 100 m, letting hot latitudes ripen balanced fruit.
- Give an example of a cold ocean current and its effect. — The Benguela (South Africa) or Humboldt (Chile) chills the coast, enabling cool-climate styles.
- What does a wide diurnal range do? — Cool nights preserve acidity and aromatics while days ripen the fruit — balance (e.g. Ribera del Duero).
- How do dark stony soils change ripening? — They absorb and radiate heat, warming the fruit zone on cool sites (Mosel/Priorat slate, Rhône galets).
- Name three defences against spring frost. — Heaters (bougies), wind machines, sprinklers (aspersion), and planting on slopes so cold air drains away.
- What happens to the vine in extreme heat? — Above ~35°C it shuts down, pausing photosynthesis and sugar accumulation, so ripening stalls.
- Why "earth up" the graft in cold regions? — To insulate the vine's most vulnerable point against winter freeze below ~−20°C.
Latitude gives a vineyard its starting temperature; altitude, the sea, the slope and the stones decide where it actually lands — and that landing point is the first thing you taste.