How to Kill E. Coli on Vegetables

How to Kill E. Coli on Vegetables. (Image: Edalin/iStock/GettyImages)

There are few salads as crisp and satisfying as a Caesar, at least until you learn that there's been a lettuce recall. A lot of different bacteria can live on your greens, and the most alarming and potentially dangerous is E. coli. The internet is filled with conflicting and often inaccurate information about how to kill E. coli in vegetables, and in this case, it's especially important to know what works and what doesn't.

Washing Vegetables Doesn't Help

The first thing to understand is that washing under cold running water won't protect you against E. coli in veggies. The water will remove surface dirt and some pesticides and a few other things, so it's not necessarily a bad idea, but it won't deal with your main problem.

In fact, if there's E. coli present, water will just spread it around more evenly from infected vegetables to not-infected vegetables. Dish soap won't kill E. coli either, and it contains things that could upset your stomach if it isn't rinsed well enough, so that's also a bad idea.

Washing With Vinegar

Some sites advise washing lettuce and other delicate vegetables with vinegar instead of water. It's true that vinegar kills bacteria pretty effectively in concentrations of 5 to 6 percent acetic acid, which is what you get with regular white vinegar. The problem is that killing bacteria in the real world is different from killing it in the laboratory. Bacteria on the glossy surface of a plate or test tube or floating free in a pool of vinegar are pretty vulnerable.

Bacteria in the cracks and crevices of actual vegetables or bacteria that have made their way inside the vegetable itself are not nearly as exposed. There's a much higher chance they'll survive and then bounce back if you don't eat the veggies right away. That's a serious issue because even a few E. coli bacteria can make you really, really sick.

Kinds of E. Coli in Veggies

The problem is that there are a few different kinds of E. coli that show up in vegetables, and one is a lot more dangerous than the others. Most varieties will give you a nasty case of diarrhea, but they aren't usually life threatening. More importantly, the number of bacteria needed to make you sick – what scientists call the infective dose – is very high, up in the millions or billions.

The dangerous one is called "shiga-toxigenic" E. coli, or STEC for short, and the specific strain called O157:H7 is the one we see most often. It can cause life-threatening illnesses even in healthy people, and for the young, old or ill it can be very dangerous. The worst part is that the infective dose for STEC is very low, just one to 10 viable bacteria. If you think risking your life – or worse, someone else's – on the chance of killing every single bacteria is a bad bet, you're right.

Cooking Is the Safest Method

The kind of vegetables most likely to contain E. coli are the ones we usually eat uncooked, like lettuces, baby spinach and sprouts. Unfortunately, cooking to a temperature of 165 degrees Fahrenheit is the only really reliable way of killing the bug.

This isn't necessarily a bad thing. Spinach is still tasty and nutritious in a soup or omelet, and sprouts are a classic stir-fry ingredient. Even lettuces are often braised or grilled in some cuisines, and sturdy varieties such as romaine can be steamed or sauteed like spinach.

A food thermometer is the most reliable way to judge when your food is fully cooked. In a soup or casserole, it's relatively easy to get an accurate temperature. It's harder with boiled, steamed or sauteed vegetables, but as a rule, by the time your greens are fully wilted, they should also be fully cooked and food safe, even if you can't find a way to get a thermometer into them. If cooked greens don't appeal to you, your best bet might be to wait until the recall ends.

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