The real sweet and sour sauce

For centuries, it was Europe's favourite flavour enhancer. Now verjuice is back in all the most fashionable kitchens. But what is it – and how is it used? By Rob Sharp

From agresto drizzles in Italian trattorias to aggourida waterfalls in Northern Greece; from the spitroasted porks of Medieval Britain to the ciders of southern France, the use of different forms of verjuice or "vert jus" – literally green juice – was widespread until it became a European "fossil food" from the 18th century. But recently this by-product of viticulture, made from crushing unripe grapes pruned from vines early in the season, is enjoying something of a renaissance.

Instead of being cooked up in Europe, modern-day verjuice is manufactured in vineyards in Australia, South Africa, California and Canada. From there, it is inveigling itself into Michelin-starred restaurants and onto the tables of experimental connoisseurs. Antony Worral Thompson and Heston Blumenthal are known to be aficionados, the latter serving it in the Fat Duck, and specialist suppliers are germinating in the unlikeliest of locations. These include the Pennine hills, and a food laboratory recreating Medieval life in a Cumbrian farmhouse. Various culinary genii hope to introduce the population at large to the delights of this tart, dynamic dressing.

Verjuice is less acidic than lemon juice or vinegar, and tastes a little like sharp apple juice. It can be used to balance salty, rich or sweet flavours in a dish, as well as to add a delicious brightness. Its flavour is light and elusive, but its advocates say a little evaporation goes a long way: they use it in deglazing meat, roasting vegetables, or even in a dessert syrup or as a refreshing summer drink with soda and ice. Its greatest strength is its versatility.

One of the people proselytising the public is food historian Ivan Day. He has been making verjuice in Cumbria since he was 14, emplying crab apples instead of grapes because he prefers their higher acidity. He says he likes the taste when he uses it to tenderise or marinade meat. Rather unusually, Day prefers historical cooking methods to modern alternatives. "My whole interest in food is passé," he says. "I always argue that people have a jaundiced view of food of the past. Many people are embarrassed by it. But I feel that English dishes of the 18th century were better than they are now."

In the early Middle Ages, large numbers of aristocrats set off for the Middle East as part of the Crusades. They shipped back the region's cooking habits, including the Muslim model of meat and fish served with fruit extract and sauce that still prevails in North Africa today. The resultant British cuisine was something sweet and sour – the latter from the addition of verjuice, the former from sugar, or things like freshly pressed grape juice, known as "must". But from the middle of the 18th century, verjuice seemed to disappear from cookbooks. The reason for this depended on the country you were in: in France, savoury food – truffles, mushrooms – was becoming more popular; in Italy, tomatoes were rolling into town; in Britain, lemons were becoming more widely available.

Another verjuice trailblazer is South Australian food polymath Maggie Beer. She has been making it since 1984, turning to commercial production in the Barossa Valley, a famous wine-producing area 60km northeast of Adelaide, in 1993. Through her 2001 book, Cooking with Verjuice, Beer suggests a little "trial and error" for those lucky enough to live somewhere hot enough to be able to grow grapes. Pick them when still green, squeeze the juice and freeze it immediately in ice cube trays. The same can be done with crab apples, passing the pressings through muslin several times to get a clear product. "You need to make sure that you have the right, low level of sugar, but in a heatwave that can change so quickly," Beer told the BBC in April. "You need to keep your senses on the alert. You need to be ready for it. I have made it every year and each time there is a different characteristic to it."

By contrast, Ron Barker, owner of High Cup wines, in the Pennine foothills of Cumbria, has been making verjuice from crab apples for four years as the weather is not warm enough for wine making. "We were hoping for a little global warming," he says. "The last year we had a decent summer was 2006, when we did make great wine. But we have a very good supply of crabapples. Our tree produces tons of them in a good year."

Jason Hunter, founder of verjuice.co.uk, sells bottles of the stuff made from a blend of South African grapes via his website. "As with anything new, it's not going to be a success overnight," he says. "There is always going to be an education process with the general public, because they don't know about it. It's one of those niche products that has only been in the hands of gourmet chefs through specialist suppliers until now. It's aimed at more health-conscious consumers who want a nice, healthy alternative to cooking with white wine, lemon juice or vinegar. The more people read about it and see it on restaurant menus, the more they will use it."

So will verjuice persist the second time around? As long as it continues to squeeze support from the unlikeliest of locations, there will always be someone heralding its unique, caustic charms.

What to do with verjuice

* Verjuice is often used as the acidic ingredient in salad dressings, when wine is served to accompany the dish. Its sour taste does not alter the taste of wine, in the way vinegar or lemon would.

* It can be drunk undiluted, to create a refreshing summer drink. It can also be diluted with still or sparkling water and enjoyed as a cordial, or even used as a cocktail mixer.

* Verjuice can be used to deglaze meat and vegetables. Once the pan juices have been deglazed, the verjuice leaves behind a gravy.

* With its sweet-sour characteristics, verjuice can be used in place of, or in conjunction with, wine and stocks. It can be used in larger quantities than the latter two.

* Verjuice can also be used in desserts. It can be reduced to create sweet-sour syrups; it also goes with poached fruit, and even cheese.

* It can also be used as a tenderiser to add flavour in a marinade for chicken, red meat and game.

Chris Powers