Originally published 6/15/2004
Packaged salad greens are generally safe. The U.S. Food and Drug Administration has set guidelines for growing and packaging greens, and so far, there have been no disease outbreaks traced to these products despite a huge volume of sales - some $1 billion per year. However, at one time, there was some concern about the low oxygen in the packages and whether or not this would affect the greens and spread disease. Low oxygen can foster the growth of the botulism toxin, but the bags designed to hold the greens have been engineered so that when the greens respire, they produce more carbon dioxide and reduce the amount of oxygen. The carbon dioxide slows the natural aging process of the greens, which retards deterioration. This has advantages and disadvantages: the produce should be fresh until the "sell by" date on the package, but don't assume that just because greens look good, they remain safe past the "sell by" date. They may not be. If you notice any spoilage, or if they are expired, don't use them.
Be cautious about produce bagged by small companies that don't have the technology of big producers and may not be using correctly engineered bags. The same goes for greens you bag at home - greens sealed in the wrong type of bag can become contaminated with harmful bacteria.
You also should look for products labeled "washed" (although "triple-washed" isn't necessarily better). Look for produce that is bright green in color and is cold to the touch. And even though manufacturers say that you don't have to wash bagged greens at home, I think you should rinse them in cold running water and dry them with paper towels before using them. (Similarly, wash all greens bagged at your local market and those you buy from open bins - even though they're labeled "washed"). And be sure to use all bagged produce within four to seven days of the date it was packaged.
As an added safety measure, I would recommend buying organic greens whenever possible. Earthbound Farm is a good brand choice.
Andrew Weil, M.D.