Throughout the 1970s and 1980s the brewery sourced raspberries from within the Pajottenland from a farm near the small village of Liederkerke. Harvested in July, the farmer would hire a group of students to come to the farm and pick the berries to fill buckets full of 20 kilograms at a time. Jean-Pierre notes that the farmer would “weigh them to nearest gram”<ref name=GrummelslinkseJune> Van Roy, Jean-Pierre. (2016a). Grummelinkse – June 2016. Musée Bruxellois de la Gueuze. Brussels, BE.</ref> and that due to Belgium’s rainy summer climate, the buckets would also be filled with quite a bit of water.
As tends to be the case with raspberries and beer, it can become quite sour and it was relatively weather dependent as to weather the harvest was acidic or sweet. Jean-Pierre recalls that “customers would be very critical when the raspberries used were of lower quality”.<ref name=GrummelslinkseJune> Van Roy, Jean-Pierre. (2016a). Grummelinkse – June 2016. Musée Bruxellois de la Gueuze. Brussels, BE.</ref> That is not to say, however, that the beer was unpopular. Van Roy recalls a time when over 600 bottles of raspberry lambic were opened over three days at the Francs-Bourgeois festival.<ref name=GrummelslinkseJune> Van Roy, Jean-Pierre. (2016a). Grummelinkse – June 2016. Musée Bruxellois de la Gueuze. Brussels, BE.</ref>
The approximate timeframe for the addition of vanilla is unknown (roughly the 1980s) but it is credited to a friend of the brewery named Guy Derdelinckx. According to Van Roy, “one day Guy suggested I try a new aperitif, whereupon he reached into the refrigerator and took out a bottle of raspberry lambic containing a pod of vanilla. When I tasted it I was pleasantly surprised because it turned out that the vanilla flavor really offset the beer’s excessive tartness. Guy had had a stroke of genius and thanks to him I was able to naturally soften the somewhat rough character of certain vintages”.<ref name=GrummelslinkseJune> Van Roy, Jean-Pierre. (2016a). Grummelinkse – June 2016. Musée Bruxellois de la Gueuze. Brussels, BE.</ref> From that point forward, the brewery used a small amount of vanilla extract in each batch.