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January 14, 2007

Helpful Hints from joeeze: How do you tell if a nut is rancid?


I'd bet not one person in a thousand knows.

Aristotle Onassis once remarked, "The secret of success in business is knowing something no one else knows."

Of course, nowadays that's called insider trading but hey, let's not be chippy.

Robert L. Wolke, food columnist extraordinaire, addressed the topic of rancid nuts in his January 10, 2006 Washington Post Food section "Food 101" column.

Long story short: You can't tell by smell: you have to taste.

FunFact: The speed with which nuts turn rancid is in direct proportion to the amount of polyunsaturated fatty acid they contain.

Fastest to slowest to turn rancid, in order:

1) English walnuts

2) Pecans

3) Brazil nuts

4) Peanuts

5) Almonds and pistachios

6) Cashews and hazelnuts

Here's the story.

    Cracking the Code

    Q. I like to eat pistachio nuts, and I prepare dishes with walnuts and almonds throughout the year. In the holiday season I also use pecans and hazelnuts. How should nuts be stored? Why do they become rancid? When shopping for nuts, either in a store or from a catalogue, what are signs that they are rancid?

    A. Before I get to your question, I must address the nomenclatural nonsense that pervades the world of nuts.

    First of all, botanists have their definition of a nut and gastronomes have theirs. To a botanist, a nut is a whole, hard-surfaced fruit containing a seed. To a gastronome, the seed alone may be called a nut. Peanuts are neither; they're legumes. But before I drive you nuts, let's just agree that anything you think is a nut is a nut.

    Second, a filbert is a hazelnut is a filbert. They come from two very closely related trees, and you have to be an expert to tell their nuts apart.

    Now about rancidity and storage.

    The oils in most nuts are chiefly the more healthful, unsaturated kind. But unsaturated fats turn rancid more readily than saturated ones, because the (double) bonds in their molecules are easily broken by oxidation. The resulting molecular fragments, short-chain fatty acids, are likely to taste and smell bad.

    Roughly, the more polyunsaturated fatty acids a nut contains, the faster it can turn rancid. On that basis, we can expect the most common nuts to line up this way, in order of fastest to slowest: English walnuts, pecans, Brazil nuts, peanuts, almonds and pistachios, and cashews and hazelnuts.

    Most nuts are harvested in the fall, so they're still fresh for our holiday party bowls or all those pecan pies. But containing as much oil as they do (40 percent to more than 70 percent), they eventually will turn rancid.

    Unshelled nuts, protected by nature's armor, will keep for a year or even two, especially if refrigerated. Squirrels are able to successfully store acorns over the winter because the cold slows the two chemical reactions responsible for rancidity: oxidation and hydrolysis, which are caused by air and moisture, respectively. So if your nuts were fresh to begin with — that is, bought from a reputable, high-volume supplier — their shells might keep them fresh until next Christmas if the nuts are stored in a cool place. (Cashews, by the way, are never sold in their shells, which contain corrosive and poisonous resins.)

    Shelled nuts, especially those that have been chopped or roasted, are more prone to rancidity. Secured in an airtight container, they can be stored for four or five months in the refrigerator and for up to a year in the freezer.

    How can you tell if a nut is rancid? In the store, sneak a sample if possible. Smell is not reliable; taste is the best test. If it tastes sour or rank, shop somewhere else. When buying from a catalogue, you just have to trust your supplier.


Now gimme that last cashew — and don't tell me you just ate it.

January 14, 2007 at 02:01 PM | Permalink


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very useful post, I am sitting at my desk in mid-January eating chocolate-covered pecans on sale from Christmas and wondering why they are so awful but the macadamia nuts are still good, and now I know why!

Posted by: ceefee | Jan 9, 2009 8:38:40 PM

Can rancid pecan nuts be freashened up by putting into the oven.

Posted by: Rooks | Sep 18, 2008 11:10:49 AM

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