We commonly assume that a darker beer is going to be full bodied and probably not good for your diet. But this may not be so commonly true.
First off, what actually makes a dark ale? Well the simple answer is dark malts, black and chocolate being very common varieties. But these can make up an incredibly small part of the recipe. Most will mainly be pale malt with maybe 5% dark. This is why some recipes, like ours, add in more ingredients at this stage to help add more body and flavour. However, a lighter colour beer may have lot more secondary malts and thus a higher sugar content.
This sugar then factors into alcoholic content. In fact, while to fit some categories (which no one can agree on anyway) like Imperial Stout you typically need 7%+ abv (alcoholic by volume) there is nothing stopping a dark ale being lower than 5%. At the same time a light ale of 7%+ is not unheard of. Especially with the growth of experimental craft beers these categories get even less clear.
A lot of Carbon Dioxide also gives the impression a drink is lighter, which is why many stouts are not very bubbly while a light ale that could in fact be fuller bodied appears to be a very light and easy to drink beer. Many brands also add nitrogen to their dark beers. As it isn’t soluble in water it adds pressure like CO2 would, however it also gives a thick feeling to the drink and also helps with the thick head. This is helped even more by special taps which have a restrictor plate. By forcing the ale through small holes as it is dispensed the nitrogen gets through while CO2 doesn’t. This I because the CO2 bubbles are larger which is partly why they have a more noticeable effect on a beer and tongue.
So, can you actually get a dark ale that is in fact light? Sure, some you already drink are likely fooling you already. You can even get dark lagers like our Schwarzschmied Lagerbier. Dark ales really are a definition down more to what we see than the actual facts of the matter. A lighter ale can have the qualities we may assume are present in a dark ale and vice versa.