Frost, flowers and the Sussex vine, by SommDom

The perils of early spring

The earliest archaeological evidence of viticulture in England comes from Fishbourne in West Sussex, settled by the Romans. In that era the new year began in March, and the Ides of March (the 15th) fell close to the point when spring was understood to begin and the annual growing cycle to restart. Nowadays, the first day of astronomical spring is the vernal equinox, which still falls within a whisker of the Ides. And it’s not just Caesar who needs to beware.

Sussex’s 160 vineyards will now be emerging from their dormant winter period: the sap is rising and the buds are ready to burst. But spring also brings the greatest jeopardy in cool-climate wine regions. A mere mention of spring frost to vignerons in places like England, New Zealand, Germany and northern France will chill their spines as much as the phenomenon itself, which has the potential to freeze to an early death the green shoots otherwise destined to bear fruit. Even before the buds start to appear, pruning the previous year’s excess growth exposes cut ends, making the canes vulnerable to frost. Sap exudes from the wounds, weeping moisture that may freeze, damaging the wood and delaying fruiting to the extent that the grapes may never reach full ripeness in time for harvest.

Bud burst is the iconic signal of promise for the year ahead. No sooner do minuscule green leaves break out than they are exposed to the risk of destruction from subzero temperatures. Different varieties bud earlier or later, so the suitability of a grape variety to the microclimate is one of many considerations when establishing a vineyard. The leading red grape in England – accounting for around 25% of plantings – is Pinot Noir which, despite bringing many challenges, is at least late-budding, making it less prone to spring frost.

Defensive strategies

A couple of months after budburst, the embryonic bunches break out into flowering. These tiny, delicate inflorescences are extremely vulnerable for up to two weeks before fruit set, when the first actual berries appear. There are various methods of defence deployed to protect these bunches from frost.

One method is ‘bougie’ candles or carbon-fuelled smudge pots placed strategically among the vines to prevent ambient temperatures falling below critical levels. These beacons also provide dramatic night-time images, as seen at Ditchling’s Ridgeview (right); the appearance is not unlike Lewes on Bonfire Night, alight with rivers of flaming torches. A more discreet means of mitigation, used by Bolney Estate in Mid Sussex, involves stringing electrically heated wires along the trellises at the right height to protect the buds.

In other vineyards wind turbines are set up to blow and break up cool air concentrations. Some well-funded operators in France and the New World have no compunction about turning to extreme measures when needed: in 2017 – the last truly cool claret vintage (not in the hip sense) – several top Bordeaux châteaux on the high plateau of Pomerol sent up helicopters in desperation to create downdrafts of warmer air. Marlborough in New Zealand has even seen a fleet of 100 choppers mobilised to protect the vines. One has to question whether such action – consuming finite and environmentally damaging carbon fuel – is ethical, for the sake of saving yet another crop of Sauvignon Blanc.

A more sophisticated method, called ‘aspersion’ and used by Stopham Vineyard, involves a network of capillary hoses with water jets that can be activated to spray just enough water to freeze around the bud and protect it from subzero temperatures. It requires technical expertise to set up and operate but can be highly effective – and far less energy intensive than methods involving heat. Or helicopters.

Flowers to the rescue

Once the vineyard has passed the hazards of spring, the next challenge is controlling weeds that compete with the vines. Tedious mowing, specialised tractor-mounted cultivation equipment for tilling, or the nuclear option of chemical herbicides, are the conventional means of weed control. Increasingly, however, the regenerative approach – working with nature rather than against it – is gaining ground. Planting wildflowers between the rows not only suppresses unwanted weeds, but also helps moderate excess vine vigour, especially in the nitrogen-rich, fertile and well-irrigated sandy-clay soils of Sussex (see ROSA #15). The flowers also attract beneficial predators of common vineyard pests.

The increased biodiversity improves the surrounding ecosystem and gives producers an environmental feather in their cap. A cluster of vineyards around Pulborough – Nutbourne, Nyetimber and Kinsbrook – all use wildflowers to enhance diversity, if not between the vines then at least around them. Rathfinny in Alfriston and Tillingham near Rye do likewise.

The Steiner way

Provocatively referred to by British Master of Wine Tim Atkin as the ‘Isis end of the organic movement’, biodynamic farming – devised a century ago by Rudolf Steiner – involves applying nine different natural preparations in the vineyard. The most famous of these ‘interventions’ is the burying of cow horns: filled with manure in winter and with ground quartz (silica) in summer, each buried and later unearthed around the equinox. The lesser-known preparations are potions made from certain f lowers (yarrow, chamomile, dandelion, valerian) and three other wild plants (nettle, horsetail and oak bark).

While some of Steiner’s ideas linked to astrology, gnomes and pest deterrence veer into pure lunacy, several of these interventions have been shown to enhance soil fertility and help protect vines from pests – contributing to healthier grapes and better-tasting wines, and certainly preferable to heavy chemical use.

Taking Steiner’s musings on cosmic influences a stage further, Maria Thun – writing in the 1950s – devised a biodynamic calendar directing followers on which days to carry out particular tasks. According to Thun, ‘root’ days are best for ploughing and planting, ‘leaf’ days for canopy work, ‘fruit’ days for harvesting, and ‘flower’ days for pruning or leaving the vines alone. True acolytes even believe that wines taste better or worse depending on the biodynamic day on which they are consumed. I would happily test this, but a paid subscription is required to know the days in advance; the merely curious, cynical or thrifty (and I am all of these) can only check retrospectively.

Floral flavours

Finally, on the subject of flowers, the ultimate reward for all this effort in producing good grapes is wine that tastes delectable. Wine is unusual among beverages in that a single ingredient – grapes – naturally transforms itself through fermentation into an intoxicating drink with a cacophony of (generally pleasing) aromas and flavours. For millennia this process was mysterious, claimed by religion as evidence of the divine, until Louis Pasteur demonstrated less than 170 years ago that yeast converts sugar into alcohol.

What remains unknown is the full extent of the thousands of chemical reactions that occur in fermenting must, and how precursor compounds in the grapes transform into acids, esters, terpenes, thiols, pyrazines and other aromatic molecules. Almost all wines consist of just two substances – water and ethanol – which together make up roughly 98% of the volume. It is the remaining 2% that determines a wine’s unique flavour and style. Within this tiny fraction sit the compounds that evoke the flavours wine lovers endlessly discuss: fruit, flowers, herbs, wood, nuts, dairy, earth, spice and stone.

No wine actually contains citrus fruit, currants, butter or spice – that would be illegal, as only grapes, yeast and a few permitted additives may be used. But through the complex chemistry of fermentation and ageing, compounds form that resemble the aromatic molecules found in those foods. Some share identical chemical structures: geranium, honeysuckle, vanilla and black pepper are classic examples. Scientific techniques such as gas chromatography can identify these compounds and explain why such flavours appear.

A few other products – sake, whisky and some ciders – are similarly simple in ingredients yet capable of immense complexity. Others, like gin and vermouth, are deliberately flavoured with botanicals (see ROSA #11). Wine, however, depends on the vine’s own flowers to set fruit, surviving the risks of a harsh spring. Wildflowers interspersed among the vines, or applied as Steiner would have us do, can enhance and protect that precious fruit. Ultimately, the fermentation of fully ripened grapes can produce such an astonishing array of flavours that it evokes the flora and countryside from which it came.