Beautifully lining the refrigerated shelves of the produce section, bags of triple washed salad offer convenience. Commercially washed produce does not need to be washed again at home. According to FoodSafety.gov, “If the package indicates that the contents have been pre-washed and are ready-to-eat, you can use the product without further washing.”
In order to reduce microbial counts in ready-to-eat produce packages, food companies use a diluted solution of either peracetic acid or chlorine to wash their produce. After washing, the produce is dried and packaged. The solutions of diluted peracetic acid or chlorine are approved by both the FDA and EPA. To ensure quality and safety, the levels of concentration are closely monitored by food companies.
Does this mean it will always be safe? No. As a consumer, you are still responsible for properly handling the produce. Even though it is clean, it does not allow for unsafe handling and preparation practices. On FoodSafety.gov, here are is an important tip to remember when storing produce “Store perishable fresh fruits and vegetables (like strawberries, lettuce, herbs, and mushrooms) in a clean refrigerator at a temperature of 40° F or below.”
At cool temperatures, most vegetative bacteria grow slowly. According to the Food Safety Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA), “room temperatures fall in the “Danger Zone,” between 40 and 140°F, where bacteria grow rapidly.” The FSIS website claims that “it is estimated that as many as 9,000 deaths and 6.5 to 33 million illnesses yearly are directly linked to foodborne pathogens (bacteria and other microorganisms that cause illness),” and “many of these illnesses are caused by food that are left out on the counter at room temperature.”
Cool temperatures can slow the growth of most common foodborne-illness causing bacteria. Listeria monocytogenes is an exception, for cool temperatures do not significantly slow its growth.
According to FSIS, “some bacteria can double their numbers every 20 minutes at temperatures above 40°F. In 2 hours, these bacteria can become so great in number that they may cause an illness or form toxins that cause illness.” The fast rate of growth is called the log or exponential growth phase.
To minimize growth of bacteria, keep your produce cool (at or below 40° Fahrenheit)!
Non-Contributor Note: A large number of food poisoning outbreaks linked to Romaine Lettuce have been identified in the US in the last 12 months, leading to heightened concern about the safety of eating salads.
 See, e.g. https://ronsimonassociates.com/romaine-lettuce-e-coli-lawsuitsfinal-report-by-fda/; https://foodrecallsinamerica.com/f/romaine-lettuce-e-coli-outbreak-grows-hus-cases-identified; https://foodrecallsinamerica.com/f/romaine-lettuce-e-coli-lawsuits-filed-as-173-victims–32-states; https://foodrecallsinamerica.com/f/romaine-lettuce-e-coli-lawsuit;