Tannin-rich foods: The Acorn

Nuts are tasty. OK, get the puerile laughter out of your system - I'm talking about the food kind: peanuts, hazelnuts, almonds, cashews (before you go botanical on my ass and yell that peanuts aren't nuts, I'm speaking in a culinary sense here. Botanically speaking, almonds, pistachios and many other "nuts" aren't nuts either). But what about that favourite of rodents everywhere: the acorn?

First of all, in a botanical sense, acorns ARE nuts. But why don't we find them alongside pecans, peanuts and brazil nuts when we open a can of mixed nuts? Are they toxic? Do they just taste bad? It being the autumn, with plenty of acorns around, I decided to try them out. First off, this was just an acorn found on the ground and not roasted or salted or otherwise processed. It passed the taste test - it was bitter, but not so vile that it couldn't be eaten. Nor did I get ill - after all, I'm not a horse.

The bitter taste and toxicity to horses is caused by the high levels of tannins, which vary by oak species. These polyphenols have documented anti-carcinogenic, anti-oxidant and anti-microbial properties (review) as well as being nutrient rich. Sounds like it might be worth patenting an acorn extract and selling it as a miracle drug through some sort of pyramid scheme. On the other hand, they are also iron chelators and can interfere with protein digestion in animals that aren't adapted. Plus the overly bitter taste would likely make them unpopular as a snack. Still, acorns were once part of a human (mostly Native American) diet, first being soaked to leach out the tannins followed by grinding into flour.

Some animals that haven't physiologically adapted to tannin rich acorns have adapted in other ways. The most obvious is by selecting acorns that are less tannin-rich. It's been suggested that some animals store their acorn cache in groundwater or other places with water access, allowing the groundwater or natural runoff to leach some of the tannins out making the nut more edible as the winter progresses. One study has shown that Blue Jays, while unadapted to a high tannin diet, consume a large number of acorns in the autumn months with no ill effects because of acorn weevil larvae that live inside the nuts and counteract the effects of tannins on the jay diet.

Canadian Thanksgiving may have passed, but acorns are still plentiful - here are some recipes that incorporate this former traditional food of indigenous North Americans.