An outbreak of listeria in Florida, United States, has caused at least one death, 22 hospitalizations and the withdrawal of an ice cream consignment since January.
Humans get sick with listeria infections, or listeriosis, from eating food contaminated with soil, undercooked meat, or raw or unpasteurized dairy products.
Listeria can cause seizures, coma, miscarriage, and birth defects. And it’s the third leading cause of food poisoning deaths in the US. Avoiding hidden dangers in food is why people often check the dates on food packaging. Printed with the month and year, it is often presented in a dizzying array of phrases: “best before”, “use by”, “best before”, “guaranteed fresh until”, “freeze by” and even a “born in” label used on some beers.
People think of them as expiration dates, or the date a food must go in the trash. But the dates have little to do with when foods expire or when they become less safe to eat. I am a microbiologist and public health researcher and have used molecular epidemiology to study the spread of bacteria in food. A more science-based product dating system could make it easier for people to differentiate foods that are safe to eat from those that might be dangerous.
The US Department of Agriculture (USDA) reports that in 2020 the average American household spent 12% of their income on food.
But a lot of food is just thrown away, even though it’s perfectly safe to eat. The USDA Center for Economic Research reports that nearly 31% of all available food is never eaten. Historically high food prices make the problem of waste seem even more alarming. The current food labeling system may be to blame for much of the waste. The FDA reports that consumer confusion over product date labels is likely responsible for about 20% of food wasted in the home, at an estimated cost of $161 billion per year.
It stands to reason that date labels are there for safety reasons, since the government enforces rules to include nutrition and ingredient information on food labels. Passed in 1938 and continually amended since then, the Food, Drug, and Cosmetic Act requires labels to tell consumers about the nutrition and ingredients of packaged foods, including how much salt, sugar, and fat they contain.
However, the dates on those food packages are not regulated by the Food and Drug Administration (FDA). Rather, they come from food producers. And they may not be based on food safety science.
For example, a food producer may survey consumers in a focus group to choose an expiration date that is six months after it was made because 60% of the group no longer liked the taste. Smaller manufacturers of a similar food could imitate and put the same date on their product.
An industry group, the Food Marketing Institute and the Grocery Manufacturers Association, suggest that their members mark foods “best used by” to indicate how long they are safe to eat and “use by” to indicate when foods become insecure.
But the use of these more nuanced legends is voluntary . And while the recommendation is motivated by a desire to reduce food waste, it’s not yet clear if this recommended change has had any impact. A joint study by the Harvard Food Law and Policy Clinic and the National Resources Defense Council recommends deleting the dates directed at consumers, citing potential confusion and waste. Instead, research suggests that manufacturers and distributors use “production” or “pack” dates, along with “use by” dates targeted at supermarkets and other retailers. The dates would indicate to retailers the amount of time a product will remain in high quality.
The FDA considers some products to be “potentially hazardous foods” if they have characteristics that allow microbes to thrive, such as moisture and a large amount of nutrients that feed them. These edibles include chicken, milk, and sliced tomatoes, all of which have been linked to serious outbreaks of foodborne illness. But there is currently no difference between the date labeling used on them and that of more stable foods.
Formula milk is the only food product with an expiration date that is regulated by the US government and scientifically determined.
It is routinely laboratory tested for contamination. But the formula also undergoes nutrition testing to determine how long it takes for nutrients, particularly protein, to break down. To prevent malnutrition in babies, the expiration date on formula milk indicates when it is no longer nutritious. Nutrients in food are relatively easy to measure and are regularly done by the FDA. The agency issues warnings to food producers when the nutrient contents listed on their labels do not match what the FDA lab finds. Microbial studies, like the ones we food safety researchers work on, are also a scientific approach to meaningful date labeling on foods. In our lab, a microbial study might involve leaving a perishable food to spoil and measuring the number of bacteria that grow on it over time.
Scientists also conduct another type of microbial study by looking at how long it takes for microbes like listeria to grow to dangerous levels after intentionally adding the microbes to food to see what they do.
Details such as the growth in the number of bacteria over time and when there are enough to cause illness are noted.
Consumers on their own
Determining the shelf life of food with scientific data on its nutrition and safety could dramatically reduce waste and save money as food becomes more expensive. But in the absence of a uniform food dating system, consumers may trust their eyes and noses, deciding to skip the fuzzy bread, green cheese or smelly bag of salad.
People might also pay close attention to the dates on more perishable foods, like deli meats, on which microbes grow easily.