Top | Ask Hank

Down with brown

(article, Hank Sawtelle)

[%pageBreakSettings nobreak=true]

Why do potatoes (and fruits) turn brown when peeled, and how do you keep it from happening so you don't have brown — or even red — hash browns?
— Jennifer H., Los Angeles, California

But they're hash browns — they're supposed to be brown, right? Of course, there are two kinds of brown — yucky brown and yummy brown. Yummy browning, which we do on purpose, comes from proper cooking, and introduces desirable flavors and textures. Yucky browning, on the other hand, is caused by a chemical reaction when plant cells are destroyed.

[%image reference-image float=right width=400 caption="Submerge your just-cut potatoes in water with a squeeze of lemon."]

Certain plant cells, when ruptured, release reactive chemicals called phenols. Like you, many animals have noticed that plants are delicious, and thus spend a lot of their time trying to eat them. One of the plant kingdom's few defenses is the production of phenols, which can irritate, attack, or otherwise bum out animals (especially bugs) that would eat them. (But one animal's phenolic irritant can be another's intoxicant — yep, I'm looking at you, cannabis.)

The plant cells also release enzymes (called polyphenol oxidases, or PPOs) that, in the presence of oxygen, link some of the phenols together into bigger molecules. These molecules include dark pigments called melanins, which provide additional protection to the plant, as well as the unappealing yucky brown color. These are the same pigments that develop (as a result of a similar reaction) when sun strikes human skin. So you could always try telling your family that the potatoes have a tan.

If for some reason that doesn't work, there are a few steps you can take to slow down enzymatic browning. 

First, the browning reaction requires oxygen, so submerging the vegetables in water as you cut them will help.

Second, the reaction proceeds more quickly at higher pH levels, so sprinkling some culinary acid (e.g., lemon juice) on the cut vegetables (or in the water) will also help. 

Finally, you can slide the whole mess into the fridge — as with most chemical reactions, lower temperatures will slow this one down. 

A lot of people claim that using a sharper knife reduces browning, presumably because it does less collateral damage to cells. I don't know if it's true, but it can't hurt.

If you want to get really aggressive, you can buy ascorbic-acid (aka Vitamin C) powder, a powerful antioxidant, to sprinkle on cut fruits and vegetables. 

Or, food-science guru Harold McGee suggests dunking cut lettuce in 115-degree water to inactivate the enzymes before draining and storing it. (I'm sure people do this all the time, right?) 

[%image hanks float=right width=400 caption="Hank's perfectly golden potatoes — dressed up with a Gruyère frico and garlic-chive oil."]

You might also try Yukon Gold potatoes if you have been using Russets for those hash browns. I find that the Yukies are quite a bit slower to brown. Since they are also less starchy, you will end up with a different end product, so definitely experiment before you have company over. 

If you've never worked with artichokes or sunchokes, get ready for a challenge, as they brown even faster than Russet potatoes. But the worst has got to be salsify. In the time it takes to strip the peel off, the root starts visibly to darken. Craziness. Luckily, no one really cooks salsify, right? (I did it on a dare.)

Enzymatic browning isn't always a naughty thing, by the way. It's what turns fresh tea leaves into delicious oolong and black teas. Who knew?

p(bio). Based in Portland, Oregon, Hank Sawtelle has engineering, legal, and culinary degrees.

hanks potatoes, l

reference-image, l

hanks, l