Bagged Salads: To Wash or Not to Wash, That is the Question

By: Christine Bruhn, PhD, Director, Center for Consumer Research, UC Davis   Date 2/25/10

With your ready-to-eat, bagged salad and scissors in hand, you might wonder whether you should just dump the prewashed greens into your bowl or take the time to wash them again. It's a question on a lot of people's minds, especially after a recent magazine review of prewashed bagged salads reported a significant number of bacteria on the greens, concluded that sanitation was not up to par, and advised consumers to wash the greens again. But is this sound advice?

An expert panel of microbiologists, food safety, and consumer experts reviewed the scientific literature to answer the question: should prewashed greens be washed again by the consumer or the food service worker? The conclusion was DO NOT rewash. Here is why:

- Consumers and restaurant workers do not adequately wash their hands, sink and kitchen equipment prior to washing. By washing again, greens could be contaminated.
 
- The bacteria that can be removed by washing was already remove at the processing facility. Washing only removes about 90% of bacteria. Additional washing would not remove much more.

So the scientific evidence gives you permission: just dump the leaves into the bowl and serve your salad.

Should I be Concerned about Bacteria in Greens?
Plants like lettuce and spinach are likely to have a large number and wide variety of bacteria, but not all bacteria is harmful. Even triple washing does not remove all bacteria because they adhere to the uneven surface of the leaves. Under refrigeration these bacteria may slowly multiply, so bacteria counts increase over time. If the bacteria is not harmful, this is not a problem.

Presence of bacteria is not a surprise and does not indicate that the greens are harmful, but if there are a few Salmonella or E. coli among the count, it is a serious concern. That is why some believe irradiation of greens could provide the extra level of safety consumers expect. Irradiation can destroy an additional 99.9% of these harmful bacteria.  The Centers for Disease Control and Prevention writes that irradiation saves lives.

Studies show that bacteria are more likely to be at the bruised or damaged portion of a leaf. Remove and throw away leaves that are squashed or discolored. These leaves tend to have an off taste, so the effect is likely to be quality, but it could be good for food safety, too.

So When and How do I Wash my Greens?
If you are selecting greens from an open bin at the market, WASH them just before you eat them. You don't know whose hands have been in the bin. What if you buy a head of lettuce or a bunch of spinach? Wash it!! It is better not to soak greens or any fruit or vegetable in a common container. If one item is contaminated, soaking will contaminate all the others because the bacteria spreads in the water.

This is the most effective way to wash your greens:

- Wash your sink, your hands, the counter, and any container you will use
- Rinse the greens under running water. Gently rub the leaf surface with you hand.
- Place greens in a clean colander, salad spinner, or rack
- Blot dry with a paper towel.

Don't forget the drying step. Research shows that some bacteria along with the moisture is actually removed from the leaf when it is towel dried rather than air dried. Use a cloth towel only if it is clean. A single use paper towel will not have been contaminated by a previous use.

What do you think? How do you prepare your salads?

Want to check the facts or learn more about the science discussed here? Read the article by Palumbo et al in Food Protection Trends 27(11):892-898 available from the International Association for Food Protection at www.foodprotection.org

More Resources on Food Safety:
www.foodsafety.gov
Irradiation Resources from the USDA
Food Irradiation: A Global Food Safety Tool
Be Food Safe with Win
A Consumer's Guide to Food Safety Risks