We’re well into fall now, which means that porters and stouts have triumphantly returned to the Black Creek Brewery. Ed’s been working hard on batches of dark beer for the cooler months. Porters and stouts are a personal favourite of mine—but did you know that they also have more iron content than paler beers?
A 2011 study in the Journal of the Science of Food and Agriculture tested 40 beers from all over the world. The researchers found that darker beers had the most free iron content: 121 parts per billion, compared to 92 ppb for pale ales, and 63 ppb for non-alcoholic beers. The study speculated the dark beers’ higher iron content could be related to the malts and/or hops used. This article I found says:
However, pale beer production includes a filtering stage in which diatomaceous earth is used. This sedimentary rock is a porous material with micro-algae used to lighten the beer; it traps the iron, causing its concentrations to decrease.
I’m not sure I agree with this.
Diatomaceous earth is the fossilized remains of diatoms: a form of hard-shelled algae. It works to filter particles from beer (among other things, including fish tanks and swimming pools). However, modern dark beers undergo the same filtering process: it doesn’t matter what colour your beer is, you’re still going to have yeast sediment and hop residue. So linking iron content to filtration process simply doesn’t make sense…
…especially when you look back to the 1800s. Modern-looking beer filtration doesn’t come about until the late nineteenth century. The first diatomaceous earth filter for brewing wasn’t used until 1930, and it didn’t really become prevalent until after WWII. In the 1800s, filtration was pretty well limited to simple hop backs (ours is lined with cheese cloth!) to strain out the hops, and finings like Irish moss and isinglass, which would at least help free-floating particles settle to the vessels’ bottom.
And yet, there seems to be a sense among Victorian brewers that porters and stouts are somehow more hale and hearty. “Porter is recommended by medical men to their poor convalescent patients,” writes William Little Tizard, in his treatise on brewing. He goes on to argue that paler beer is easier on patients’ stomachs, but it’s a good indication that darker beers were considered beneficial for the weak and run-down.
Part of me would wonder if it’s a trick of the taste buds. Porters and stouts have a higher proportion of more darkly-roasted barley. The longer you kiln barley, the more chocolate/coffee-like flavours it develops. Simply put: it tastes stronger. This is why people brace themselves for Irish dry stouts, even though they’re usually under 5% ABV.
Except that modern study shows there is quantitatively more iron. So I wonder instead if a longer kilning period somehow makes the iron in barley more available for absorption (and there is a surprisingly high level of iron in barley—3.6 mg per 100g, higher than spinach at 2.7 mg/100 g!). From what I can tell, iron content in hops is negligible, and pale beers tend to have more hops anyway…
In any case: whether kilning affects available iron or no, if we feel the darker beers are more fortifying, that might be enough. Maybe share a growler with your friends, and see what you think.