2010: Mechelen brown beer
Bières brunes de Malines
There are some similarities to beers like Rodenbach here. A long boil to develop colour, and then blending a small proportion of aged beer with the fresh stuff. Of course Mechelen isn't all that close to Roeselare so who knows.
I believe Het Anker (or one of its previous incarnations) was brewing in Mechelen at this time, but somehow I doubt Gouden Carolus would taste much like the beer below.
Original text here.
In this city, they brew two varieties of brown beer, once very famous around the country, and they do not fail to remain rather important, though they don’t export as much as before. These two types of beer are prepared using a mixed grist, usually composed of one part oats, two parts wheat and four of well-modified barley, which is dried in the wind to start, then finished on tourailles, as is done in Diest, for the brown beers of which I speak.
For a brew of 37 casks of 225 liters, of which 22 casks are strong beer, they employ an average of 2100 pounds of malt, 1100 pounds of wheat and 550 of oats, mixed and ground together. These starchy materials go into a very shallow mash tun, with a capacity of 50 hectolitres where they first add enough warm water to slightly dampen the grist, then there is an addition of 18 to 20 hectolitres of boiling water which is mixed thoroughly, then allowed to stand for fifteen minutes, after which, in baskets and small pans, they remove as much liquid as they can and add it directly to a boiler called a slym ketel in Flemish; and then while they carry out a further mash with moderately hot water, the boiler that contains the first mash is heated, and once it is boiling they add the second mash which is extracted in the same manner as the first. Some brewers do not wait for the first mash to boil before adding the second, on the contrary they hasten to remove it from the mash tun as quickly as possible, in order to add it to the first before it reaches a boil, and boil for half an hour with the two mashes together; after which they pour the boiling wort back on the malt in two or three parts; they fill the mash tun and it is stirred for a moment, then allowed to stand for half an hour, then is run off clear to the holding tank which has previously been well cleaned. Once the filtration is started they continue to empty the wort from the boiler into the mash tun until it is completely empty, then it is cleaned and the wort is transferred back across to the boiler where it undergoes a boil of 10 to 12 hours with a pound of good young local hops per hectolitre of wort.
This wort clarifies as usual, cools on trays to a temperature suitable for prompt fermentation, receives an average proportion of yeast and is what we call strong beer or double Mechelen brown beer.
When one wants to prepare the regular brown beer they add to the first boiler a third mash that is small enough to give, with the first two mashes, 28-50 casks of beer, and in this case they make only eight to ten casks of small beer which is prepared with a fourth and final infusion used to completely exhaust the malt in the mash tun. In the first case the last two mashes are used to prepare the small beer which yields 15 to 18 casks for the proportions of raw materials mentioned above.
The Mechelen brown beers are very dark in colour, due mostly to the long and rolling boil that they undergo; one can generally judge the future quality of a brew by the greater or lesser ease with which the wort darkens. It augurs ill for those who darken with difficulty, and they are generally in the habit, in this case, of adding a few handfuls of lime to the boiler, which does not fail to quickly improve the colour at the expense of its quality, contrary to the general opinion among brewers and especially the public who judge these beers in part by their colour.
Previously these beers were only brewed in winter, i.e. November to April, and were not consumed until after eight to ten months, with an added eight to ten per cent of fresh beer, that is to say brewed only a fortnight earlier, to make it foam after a few days. Today, they brew almost all year, except during times of extreme heat, and the beer is served after one to three months or more, cutting with a third or quarter of old beer, of one year to 18 months, which gives the mixture the particular taste of old beer.
After being mixed they are always given a good fining before delivering the beer, which then clarifies after about five to eight days.
 (1) This makes about 37 kilograms of grain per hectolitre in the mash tun.