Since the first vintage of Winter Ferment in 2017 the wine has won numerous accolades, including spots in the FNB Top 10 Sauvignon Blanc Competition and the Sauvignon Blanc Trophy at the National Young Wine Show.
In a quest for optimum tropical fruit expression in Sauvignon Blanc, Thys Louw, owner-winemaker at Diemersdal, released the first Winter Ferment in 2017. The wine is made by freezing the grape must to -20°C soon after the grapes were harvested in February. The frozen must is thawed in June, inoculated and allowed to ferment as per normal.
Although, according to Louw, the results of this freezing and late “winter” ferment have been anything but normal.
“For reasons unknown, the wine is showing flavours and chemical analyses I have never encountered in any of the Sauvignon Blancs made at Diemersdal,” says Louw. “The primary feature is the high occurrence of thiol compounds. These thiols are what gives Sauvignon Blanc the passion fruit and gooseberry flavours for which especially the wines from New Zealand have become famous.”
Louw says that while a high thiol count for a tropical style of South African Sauvignon Blanc amounts to 2 500 nanogram per litre, the Winter Ferment Sauvignon Blanc measures in the region of 5 000 nanogram per litre.
“This high thiol level is unheard of in South Africa and is more in line with what one would find in wines from Marlborough in New Zealand,” he says. “When I set out with the idea of freezing must, I wanted to see what the effect would be on the freshness and the complexity of the wine, including a possible increase in thiols. But no way did I expect the frozen juice to deliver a wine with double the thiol level we at Diemersdal had become accustomed to and with such extraordinary tropical flavours.”
The grapes for the Winter Ferment were night-harvested at 23 degrees Balling, with crushing and destemming done reductively. Skin contact of three hours was followed by pressing and the juice was allowed to settle for 48 hours after which it was frozen. The fermentation of this wine was postponed for four months before being inoculated with CKS yeast. After two weeks alcoholic fermentation at 14-16oC, the wine was bottled.
Louw describes the wine as the most “New World style of Sauvignon Blanc” he has made. “The wine has intense aromas of gooseberries, tropical fruit and sweet grapefruit with a core of minerality. Besides the intense fruit expression, the excellent natural acidity creates balance to the concentrated, rich mouth-filling texture.”
Besides winning various accolades since its release, Winter Ferment has been an instant hit with the consumer. “The wine began as an experiment but has, fortunately, turned into a commercial success,” says Louw. “As a stalwart in the range of Diemersdal Sauvignon Blancs, Winter Ferment opens a new world of complexity and depth to the lover of this grape variety. Unlocking the potential of Sauvignon Blanc and showing what this grape can do is an integral part of Diemersdal’s ethos. We don’t know what we’ll try next, but if there is an opportunity, we’ll take it. As the Winter Ferment has shown, the possibilities in the wine world are endlessly exciting.”