Instead of trying to write a detailed description of Meerts production, I'm going to direct you to read Hors Catégorie's write up. As far as I've found, it is the most complete description of Meerts and was the primary resource I used in trying to recreate this beer.
In this article, the 1800's brewery's poor efficiency rate is mentioned, which was echoed in other conversations I had. I was told that modern brew systems/grain are too efficient to create Meerts from lambic second runnings and that the brewers making it today have a dedicated brew day (again, I don't know the details of Boon and Cantillon's Meerts production). Last year I tested this out, and on a 50 bbl brew house, I hoped to get 20-30 bbls of second runnings to create a Meerts the old way. About 4 bbls into the second runnings, our pH jumped and gravity dropped to near zero. We were pulling water at this point and I called it off.
Still fascinated by what this style of beer could look like, this year we dedicated a brew day to Meerts, and in February filled 2 foeders. I believe we are the first to make Meerts in the US. To make it, we essentially took our turbid mash recipe and scaled it down to target 4%, and slashed the amount of hops since Meerts traditionally received the post boil spent hops from lambic.
|Sample of Meerts from the foeder.|