In celebration of BrewDog's stunning Semi-Skimmed Occultist launch, we look at what makes dark beers so complex and delicious

The Maillard reaction is a beautiful thing. A reaction between amino acids (stay with me) and sugars that makes food, and beer, taste amazing. It is, in short, the browned crust on a steak, the golden shine on a brioche and the darkened onions on your hotdog. So what does a chemical reaction, first discovered by French chemist Louis-Camille Maillard in 1912, have to do with this month’s Beer Club focus on the indulgent dark beers we’ve included? Well, pull up a chair and crack open your Semi-Skimmed Occultist.

The beer you’re pouring into your glass is dark red with a sumptuous creamy head. The taste? There's a rich hint of chocolate and coffee.

Firstly, that beautiful dark colour, one that leans towards what we’ve seen in a stout, a porter, a black IPA, a black lager, well that’s all down to the Maillard reaction. Malted grain, germinated cereal grains that have been dried in the malting process, is the bit that gives beer its sugar and therefore its alcohol.

It’s the same grain that is used to make whisky, malt vinegar and, er, Maltesers. Homebrewers will recognise the Horlicks and Ovaltine aromas from the wort they make – that’s because it’s all the same stuff.

To malt the barley, the most common grain in beer, it needs to be heated in an oven – a highly skilled process – during which time it is ‘toasted’. And just like that slice you’ve got under the grill, it can be toasted very lightly or until it’s almost burnt. That Fastenbier in front of you, it’s the addition of darker, more toasted grains, that gives it that colour.

So that’s the colour, what about the flavour? Well, it’s virtually impossible to drink a dark stout or porter without it conjuring up associations with coffee and chocolate. That’s no coincidence; barley goes through almost exactly the same process as cacao and coffee beans. Yep, it’s the Maillard reaction again.

With the naturally occurring flavours of chocolate and coffee, it wasn’t a great leap of imagination by brewers to start adding coffee and cacao to further enhance these luscious flavours, and combining them with complementary ingredients such as vanilla, caramel and salt. On that note, it’s probably time to open another one.