Editor's note: Bob Hutkins is the Food Doc. He is a professor at the University of Nebraska-Lincoln, where he teaches and conducts research in food science and food microbiology. Send your questions on any topic related to food, food safety, food ingredients and food processing to the Food Doc at email@example.com. His column runs monthly.
I have two questions. First, I read that adding raw potatoes to an oversalted broth removes the salt. Is this true? I also have observed that if I thicken a seasoned broth with flour, I have to add more salt. Does the salt get trapped in the starch structure?
Although there is a grain of truth to this method, it’s not because the potato actually absorbs salt from the broth. Rather, the reason the salty taste is seemingly reduced is due to the principle of diffusion, which describes the movement of water and other molecules in mixtures, such as food.
Think of a potato as a very wet sponge (surprisingly, potatoes are 80 percent water). When added to the broth, the water inside the potato and the salty water in the broth are free to move back and forth until equilibrium is reached. Thus, the potato becomes a little more salty and the broth a bit less salty.
The limitation with this method is that it relies on simple diffusion and is, therefore, rather slow. So even though this practice would work somewhat, you would have to add several potatoes to notice much of a difference.
Regarding your second question, there are several explanations for why adding flour or cornstarch to thicken a broth would appear to reduce the saltiness. First, flour and other thickening agents have a bland flavor, so when these substances are added to a broth or sauce, the flavor intensity and saltiness are diluted.
Secondly, adding flour or starch to a broth also affects flavor perception because of the coating or masking effect starch has on our taste buds. In addition, the thicker the sauce, the less mobile are flavor and salt molecules, meaning the molecules are slow even to reach the taste receptors in your mouth.
These are, by the way, great food science questions.
How did cantaloupe all of a sudden get to be so dangerous? Doesn’t the rind prevent harmful bacteria from contaminating the fruit?
Actually, the emergence of cantaloupe as a potential source of foodborne disease is not so recent. Small, sporadic outbreaks have been reported for nearly 30 years.
However, without a doubt, the listeria outbreak that occurred in 2011 involving cantaloupes grown in Colorado was the largest and most serious, with many illnesses and even fatalities. Again, this summer, cantaloupe from Indiana appears to be the cause of a nationwide salmonella outbreak.
Cantaloupe, of course, has a thick, tough rind that protects the fruit from microbial invasion. However, cantaloupe grow on the ground and are exposed to listeria, salmonella and other pathogenic bacteria that have contaminated the soil.
Once they find their way to the surface, the nooks and crannies provide a safe haven for these bacteria to escape and hide. Then, when the melon is cut, the bacteria literally are dragged through to the fruit surface. Refrigerating the cut-up fruit is important but is not a total fix, because some bacteria, especially listeria, can grow at refrigeration temperature.
Consumers should follow the advice from the FDA, the Centers for Disease Control and other food safety experts who recommend scrubbing the cantaloupe rind (before cutting), preferably with a vegetable brush. Bruised or blemished cantaloupe should not be eaten. The cut fruit should be refrigerated promptly; cantaloupe left at room temperature for more than two hours should be discarded.
Ultimately, even an educated consumer can do only so much. It is up to growers, distributors and regulators to adopt post-harvest decontamination and other farm-to-fork practices to ensure the safety of cantaloupe.