A yearlong study of 199 consumers by the Center for Consumer Research at the University of California, Davis, found just 47% washed lettuce as prescribed by food safety experts — hand rubbing leaves under running water.

The majority fell into other categories, including 15% who didn’t wash iceberg or green leaf lettuce at all while preparing salads.

“Twelve percent soaked their produce, which is not recommended,” said Christine Bruhn, the center’s director. “Because if you have contamination on some of the leaves, it gets in the water and spreads to all of them.”

The results were recently published in the journal Food Protection Trends by researchers Bruhn and Ho Phang. It’s the first of two expected papers. The second will focus on how the same consumers handled and cooked hamburgers.

Meat and salad preparation was videotaped by researchers in consumers’ homes, most in Northern California. Researchers provided the ingredients — which also included tomatoes and celery — plus a $50 Target gift card to participants. Later, they distributed flyers on safe vegetable and meat handling, along with refrigerator and meat thermometers.

Other food safety practices studied included how washed produce is dried and whether tomato stem scars are removed.

Most shook water off their lettuce (58%), tomatoes (75%) and celery (81%) — not the safest drying method, according to Bruhn.

“I often do that too,” she said. “But microbial assessment has shown when you dry, blotting with a clean paper towel is an important part of the sanitation process. Generally people have not paid any attention to drying. Shaking does not remove enough, and cloth towels could be contaminated.”

For tomatoes, only 27% of the volunteers removed stem scars. But studies have shown that more bacteria can be found there than elsewhere in a tomato, Bruhn said.

“Cutting the stem scars is good from a food safety perspective, but I’m not sure they were thinking about food safety,” she said. “They don’t look good. But we’re asking food safety educators to add that to their message.”

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While the researchers found consumer produce handling in need of considerable improvement, they also said that even ideal home practices would not ensure food safety by themselves.

“If there’s contamination in the field, how effective is home washing?” Bruhn said. “You only remove 90% to 95% of the bacteria when you wash really thoroughly at home. That’s why it’s important the product the consumer receives has the lowest harmful microbes as possible. It’s important that they do their part, but even if the consumer does it as well as they possibly could, it’s not a solution to the microbial safety of fresh produce.”

Tracking the number of foodborne illnesses due to contamination caused in the home is difficult, Bruhn said.

“It’s really tough to know that,” she said. “If something is contaminated in the field, you will likely have a large number of people become ill from it. That’s the type of incident where local and federal health authorities see the statistics and trace it back. But if contamination occurs at home, those are sporadic. There are sporadic cases all the time, and of those we know only some who become quite ill. Many are not reported because they don’t end up in the hospita