Frank Boon opened his new brewhouse in March 2013, which means that when we visited, they were about a month away from reaching a landmark age. Three years means a lot to lambic brewers: it’s the age at which you have your old lambic, which when blended with young lambic gives you the uniquely Belgian beer known as geuze.

Boon is the largest of the remaining traditional lambic brewers, although he’s dwarfed by the big breweries making fruit beers – people like Lindemans and Mort Subite. He not only blends his own geuze, he also makes an Oude Kriek and supplies lambic wort to blenders including Tilquin, Hansen, Oud Beersel, De Cam and 3 Fonteinen. His fingerprints, then, are all over the Belgian lambic world.

The new brewhouse was needed to increase production and improve efficiency, as well as being more energy-efficient, a consideration he thinks will become more and more important as time goes on. “You won’t be able to be a brewer in the future if you don’t think about saving energy,” he says.

Boon started in 1975, at a time when it must have seemed that the gueze and lambic trade was on its last legs. Now it’s the trendiest beer on the planet, with brewers worldwide trying to replicate its unique character. The question is: was he incredibly foolhardy, or remarkably prescient?

His first enterprise was a brewery in Halle, just one stop down the railway line from Lembeek, where he is now based and which allegedly gave lambic its name (though opinions vary). His parents thought he was mad. “We’d had a brewery in the family that closed in 1970 and my parents were so happy it was gone, but my father told me OK, you do what you want, but not one franc from the family.”

He went ahead, and within two years had gathered enough capital to convince the banks to lend to him, and he bought the brewery owned by Rene De Vits, one of two lambic brewers who he considered at the time to be producing a worthwhile product. Rene had a brewery and blending shop. His sister ran an adjacent cafe, which received his very best output, and there was a small shop selling to the public.

“He had no successors and he put the brewery up for the price of the building, so that’s how I started. It was very old-fashioned. There was no electricity on the first floor. When I asked him why, he asked,’are you planning to work through the night?’” He moved finally from Halle to Lembeek five years after acquiring De Vits, but still owns the property. The whole building is full of boxes of Mariage Parfait ageing, he says.

“People thought I was crazy,” he says. “The only guys who were still active or saw a certain future were Jean-Pierre Van Roy of Cantillon and Henri Vandervelden (the third generation of the founding family of Oud Beersel, who stopped brewing in 2002, to be restarted three years later by Gert Christiaens and Roland De Bus), but they saw it more as a museum, with geuze as a thing of the past.”

He received support – which was difficult to overestimate in those days – from beer expert Michael Jackson, who referred to lambic beers as “the champagnes of the beer world” and brought Frank together with other luminaries of the beer world for lunch in his series The Beer Hunter, in an episode called The Burgundies of Belgium, which can still be seen on YouTube.

“I had a lot of discussions with Michael Jackson. He visited in I think it was 1977; I was still a blender and I advised him to visit the lambic breweries,” he says. “The discussion was always about the technical side of making quality products as well as the visual side. He said people like the wooden casks with cobwebs and sun shining through the dusty windows, old glasses and enamel bottles. If you’re too modern it will handicap your sales. I argued that quality is important: you can’t sell third-rate beer with a nice story. I think some brewers made the mistake of thinking it wasn’t possible to achieve quality in lambic. For many of them, time stopped in 1880 or 1890, and they just kept on doing what their fathers and grandfathers had done.”

His brewery looks nothing like a museum, but he’s managing to produce beer of the highest quality, in demand not only from the beer-loving public but also industry insiders. So where does he go next?

“I’m not chasing hectolitres. I’ve been doing this for forty years, and the balancing act makes me crazy; just to do fine-tuning, to make it more elegant, to make it more fantastic,” he says. “If I want to experiment it would be with another cherry variety. Cherries are more interesting. I know there are still a lot of chapters on kriek still unwritten, so there’s still a lot of work I can do.”

Sweet, sweet sour

For anyone who ever dreamed of getting into the business of making lambic beers, here’s a piece of advice: Don’t be crazy.

Not only are you at the absolute mercy of a bunch of micro-organisms for a result that’s either success or disaster. Not only do you have to be based in a small part of a small country for those organisms even to be present. But if it all works out with your lambic base, you won’t be able to even make your geuze for three years, which means you’ll need space to stock the casks you’re filling in the meantime. Pierre Tilquin had to work in a bank to live during that time, while storing the lambic he bought in the meantime.

You’ll also be facing stiff competition. As you can read elsewhere, existing brewers and blenders are ramping up – with the exception of Girardin, who certainly could if they wanted to. Frank Boon is increasing his production in his new custom-made brewhouse : “The place was specially built to our own design,” he says. “The companies who sell brewhouses aren’t geared up to supply a lambic brewery.” Tilquin is thinking seriously of starting to brew as well as blend.

Other than that, it’s all fairly simple. Take a mixture of 40% unmalted wheat and 60% lambic malt. Mix it with hot and cold water to the right viscosity then pump it into the mash tanks, adding aged hops for their preservative function, making sure they remain below the taste threshold. Now boil the lot for four to five hours.

Boon uses a process known as turbid mashing, in which a kind of milky wort is drawn off into another tank, boiled and then returned to the mash tank. The aim is to maximise extraction from the large proportion (40&) of unmalted grains, to saccharify the wheat and remove most of the glutens. “If the wort is too rich, it’s overtaken by bacteria,” Frank said. “It has to be a poor wort for the making of lambic, which is selected for wild yeasts. You can make lambic with any kind of mash and you will always have a kind of result.”

But it won’t be a lambic as we know it, which is the product originating in this part of the world, and produced by this traditional method. Just as Champagne and Parma ham are defined by their process and their origin, so lambic made elsewhere by another system would not be genuine lambic.

“Those who only drink lager might think that lambic is a way to make sour beer, but in the old days, every beer that was brewed went sour after only a few days. Lambic was a way to make a beer with a balanced sourness. Not too sour – about the same level of sourness as a good glass of wine,” Frank explains. “The lambic process aims to make a beer with very high stability that can age for one, two or three years without problems.”

A beer that was too sour was considered poor quality, and if there was acetic acid or vinegar developing it would be sold not for drinking, but as gueuze cuisine, a sort of malt vinegar for use in the kitchen.

Then the lambic goes to the casks, or foeders, and there begins a whole new process of maturing and fermentation, and a whole new skill set on the part of the brewer or blender. The wild yeasts brought in from the cooling vessel survive in the oak of the casks, using an enzyme to break down the wood sugars allowing them to live in the first millimetre of the wood. That microfloral environment is crucial: Boon has three foeders he bought in 1986 which are still in service, used only to mature three-year lambic.

An old foeder like that is filled with fresh wort from the cooling vessel, and starts to develop. “But if you use it for only three-year lambic then the soil it grows in, the medium in which it develops, is three-year beer, and that combination produces lots of other enzymes that develop a wonderful taste. That’s why very old foeders are so fantastic for lambic. They give a taste that you can’t develop in a new foeder. That’s why we care a lot about old foeders.”