FAQs Answered By Our Board Scientists: on Chickens, Bananas, Old Salad Dressing, and More

banana hangerIs chicken sold at a farmers' market safe?  Why do some people hang up bananas?  If a bottle of salad dressing has no use-by date, how can a consumer find out if it's safe to use? Scientists serving on the Shelf Life Advice Advisory Board provide answers to these and two more food-related questions. Even if the questions are not one you'd ask, you'll find the answers interesting and enlightening.


Why do some people hang bananas on a special rack?

Food process engineer Dr. Timothy Bowser explains: "Bananas (and many other fruits) store best when hanging or spread out in the open air.  The improved air circulation helps to remove natural gases (ethylene) that the fruit emits that signal it to ripen.  Storing fruit in a paper bag or a big pile in a plastic bowl does the opposite.  It allows the ethylene to concentrate and, as a consequence, the fruit ripens faster."


Are raw chickens sold at a farmers' market as safe as those sold in stores?

Recent research suggests that they're not. Many farmers' market vendors of raw poultry may be exempt from USDA daily inspection requirements.  Food scientist Dr. Catherine Cutter co-authored a study that compared raw farmers' market chickens with those on sale at various Pennsylvania supermarkets.  The farmers' market chickens had significantly higher levels of contamination. The report concludes that these results demonstrate 1) the need for more food safety training for farmers' market poultry vendors and 2) the rationale for further research into the safety of other food sold at farmers' markets.  Note: Keep in mind that it is common for all poultry to be contaminated with pathogens that can be killed if the meat is properly cooked.


Is silicone cookware safe?

Food scientist Dr. Karin Allen provided this answer:


Silicone rubber cookware is generally very safe up to the maximum temperature recommended by the manufacturer (usually around 450°F). 


“Silicon” is a chemical element, and “Silicone” is an organic polymer made up of various siloxane groups (silicon, oxygen, carbon, and hydrogen).  Some of the smaller siloxanes have been linked to health conditions, and there have been studies evaluating the content of these siloxanes in various household products.  Furniture polish, lotions, antiperspirant, and hair care products were shown to contain much higher levels of these compounds than silicone rubber cookware (spatulas, cake pans, etc.).  Inhalation is the main way these siloxanes enter our system, and  research into the potential health threats is ongoing. However, only very small amounts can be absorbed by the skin (e.g. from a lotion), and even less is absorbed via ingestion.  Other studies have shown that siloxanes do not leach into food from cookware under normal usage conditions.


"As far as “chunks” of silicone rubber ending up in your food, it is chemically inert and should just pass through. Silicone rubber is actually used to make esophageal stents (from a higher grade silicone than that used for cookware, of course)."


Dr. Allen likes silicone cookware because, she says, it's easier to keep clean and bacteria-free than wood, plastic, or metal.


NOTE: For more information about silicone kitchen items, see "Kitchen Gifts for Newlyweds or Grads."  Also, see "Expert Advice on the Selection and Care of Cookware."


When I want to boil water (to cook pasta) as fast as possible, should I use a taller, narrower pot or a shorter wider one?  Assuming the pots are the same material and the amount of water is the same, which pot would boil faster?


If you believe folk wisdom, the answer would be that a watched pot never boils. But here is the scientific answer from food scientist Dr. Clair Hicks:  "The speed with which the water would boil depends upon the amount of heat it would receive.  If the pots are uncovered, the pot with the larger diameter would have the greatest evaporative loss and would come to a boil after the taller pot.  If covered pots are put on a large electrical heating surface, the wider pot would transfer more BTU than the smaller diameter pot; the small pot would not cover the full surface of the heating element, so it would boil later.    


Food process engineer Dr. Tim Bowser makes some of the same points and others:   "A lot depends on the cooking surface/method. The taller pot probably has a smaller base diameter and that is part of the answer. The base picks up most of the heat from the source and transfers it to the water/spaghetti. If you are using gas heat and the flame licks up around the base of the pot, then you are wasting a lot of heat because it’s just going up into the air around the pot. The same thing is happening if the bottom of your pot doesn’t completely cover the electric element. You should select a pot that is going to give you the best contact with your heat source. If both pots have good contact, then I would expect that the difference between the boiling times might not amount to enough to be concerned about.


"Once the water is boiling, the shorter pot will most likely lose energy faster, because more water surface is exposed to air compared to the taller pot."


When cleaning my kitchen cabinet, I found some sealed salad dressing with no "use-by" date.  I may have had it for 3-4 years. How can I find out if it's still safe to use and likely to taste okay?


Let's begin with a few reminders: 1) Use-by dates are about quality, not safety.  2)  A use-by date tells you the date that the product begins to deteriorate from its peak quality level.  3) Most products are both safe and tasty well past the use-by date.  


Even so, many people want to know that use-by date.  On a packaged product, that shouldn't be difficult to find out. Here are the steps I recommend:


  •  ŸIf it's American-made, there's likely to be phone number for the manufacturer's customer service.  Call, with the packaging in hand to answer questions, and someone on the other end should be able to tell you the use-by date and perhaps how long it might still be okay even after that date.
  •  ŸIf there's no phone number on the bottle or the number has been disconnected, check the manufacturer's website. Click on "Contact us" (usually on the bottom of the screen).  You should find a phone number and/or a link to an email box.  Use one or both.
  • ŸType the product name and the words "shelf life" into the search box on this site's home page. You may find an answer there.
  • ŸIf none of these efforts work, our advice is to discard the product, especially if you think it's quite old. If it's very dusty and/or the label is frayed, those are bad signs.


Now, here are the specifics that accompanied this salad dressing question: The name on the bottle read, "don roth's blackhawk spinning bowl dressing" (no capital letters). The restaurants that served this dressing are now closed. The age of this particular bottle remains a mystery. In this case, I feel comfortable with a recommendation to "feed it to the garbage."  Nevertheless, I sent the question, along with a list of the ingredients, to three of our Advisory Board scientists. I told them to assume that the product might be at least 4 years old.  All three scientists seemed more concerned about the product's taste than about a health risk.  However, Dr. Cutter pointed out that an old open bottle could develop mold, which would be a food safety issue. 


Here's what food scientist Dr. Karin Allen said:  "Commercial mayonnaise and salad dressings are actually pretty safe because of their low pH and water activity, so it shouldn’t be a safety issue.  The things that typically grow in these products are molds and yeast. There are a few types of bacteria that can grow, but these are all associated with spoilage (meaning they won’t make a product unsafe).  The ingredient list includes potassium sorbate and sodium benzoate, which are specifically added to control mold and yeast growth after the bottle is opened. (They won’t grow without oxygen, so they’re usually not a huge issue until the bottle is opened and more air is introduced.) If the unopened bottle has swollen, spoilage bacteria have grown.  This sometimes causes emulsified dressings to visibly separate as well.


"From a chemical standpoint, a lot can happen to make the dressing unappealing even if it is safe.  In vinegar and oil type dressings, exposure to heat or light may cause the oil to go rancid.  Many of the other ingredients that can function as antioxidants (spices, fruit extracts, citric acid) remain in the vinegar-based portion of the dressing, so they don’t do much to protect the oil.  For emulsified dressings, it gets more complex.  It partly depends on how the oil droplets are stabilized within the dressing. Some emulsifiers can actually speed up the oxidation process (meaning the oil becomes rancid).  In the case of the ingredients in this product, lecithin from the egg yolk is the main emulsifier, but the hydrolyzed soy protein and some other components should help stabilize it as well.  The biggest issue is with egg yolks (as opposed to adding purified lecithin) because you end up adding a fair amount of iron, which shifts oxidation into high gear.  If it’s bottled in a way that removes most of the oxygen and packaged in a bottle that prevents migration of gasses (meaning glass [This product was packaged in glass.]), this will slow down oxidation significantly but not stop it.


"It might be interesting to open the bottle and see if it smells bad. [It didn't.]  I personally wouldn’t eat it regardless of how it smells, but that’s just to protect my taste buds!"


Food scientist Dr. Joe Regenstein offered this unexpected suggestion just in case the owner of this bottle is really in love with don roth's salad dressing and eager to save the contents: "I believe that the pH would be low enough so that bacteria wouldn't have grown in it.  But, if I really wanted to be safe, before even doing an initial taste test, I'd pasteurize the product.  I'd start with boiling water (removed from the stove).  When the bottle is inserted in the water, the temperature will drop to about 170-180°F. The bottle should be shaken and the water stirred from time to time. This procedure should be continued for 10 minutes.  I've never done this, but the heat treatment certainly will help with bacterial kill if the salad dressing was contaminated."  I would then put the bottle into cold water to cool it down and then taste a small amount.  If it had ANY off flavor, I'd discard it."


That's more trouble than I'd go through to save a bottle of dressing that won't reveal its age.  I prefer the oft-quoted rule about food safety, "When in doubt, throw it out."  And all three of the scientists quoted above agreed.  Regenstein agreed reluctantly since he's concerned about excessive food waste in the U.S. and elsewhere.  Therefore, he tries to "save" products whenever it's safe to do so. 





Karin E. Allen, Ph.D., Utah State University, Dept. of Nutrition, Dietetics, and Food Sciences


Timothy J. Bowser, Ph.D. , Oklahoma State University, Dept. of Biosystems and Agricultural Engineering


Catherine N. Cutter, Ph.D., Pennsylvania State University, Dept. of Food Science


Clair L. Hicks, Ph.D., University of Kentucky, Dept. of Animal and Food Sciences


Joe Regenstein, Ph.D., Cornell University, Dept. of Food Science


Scheinberg, Joshua, Doores, Stephanie, and Cutter, Catherine N.  "A Microbiological Comparison of Poultry Products Obtained from Farmers' Markets and Supermarkets in Pennsylvania" Journal of Food Safety, 2013.




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