How Does It Work
The zipper-lock plastic bag you used was most likely made out of a polymer called low-density polyethylene (LDPE). It’s one of the most widely used packaging materials in the world. LDPE is low in cost, lightweight, durable, a barrier to moisture, and very flexible.
Think of the polyethylene molecules as long strands of freshly cooked spaghetti. The tip of the sharpened pencil can easily slip between and push apart the flexible strands of spaghetti, but the strands’ flexible property helps to form a temporary seal against the edge of the pencil. When the pencil is removed, the hole in the plastic bag remains because the polyethylene molecules were pushed aside permanently and the water leaks out.
As you might have discovered, it’s much easier for the stretched plastic to seal around the smooth sides of a round pencil than the straight edges found on other pencils. Hopefully you discovered this tip during practice and not while the bag was precariously positioned over someone’s head.
Take It Further
Try experimenting with plastic bags of different sizes and thicknesses. The thicker the bag, the harder it is to get the pencil to pass through. For a really thin bag, use a plastic bag from the produce section of the grocery store. Experiment with different sizes and shapes of pencils. Some pencils have flat edges while others have perfectly round, smooth edges. Which type of pencil works best?
This next gem is an extension of the “Baby Diaper Secret” activity. Collect the superabsorbent powder from the lining of two or three diapers. After all of the pencils are pushed through the bag, carefully open the bag and sprinkle in the superabsorbent powder. Give the powder a few seconds to solidify the water and remove the pencils.
Use “The Leakproof Bag” as an object lesson for a message on school spirit and leadership.
Let the bag of water represent the student body and use the pencils to demonstrate the excitement of school spirit (spear-it!).
Each pencil represents a different element of school spirit—teamwork, pride, unity, attitude, dedication, and fun.
As the pencils pass through the water, the student body helps to magnify the message of involvement and participation in school activities throughout the year. What happens when the spirit pencils are removed? Is it possible to stop the leaks? How do we keep the enthusiasm alive?
Collect the superabsorbent powder from the “Baby Diaper Secret” in a cup and label it “LEADERSHIP.” With just the proper amount of leadership, the student body is forever changed.
Despite modest improvement in some numbers, our findings suggest that most companies' safeguards might be inadequate. To tease out what might account for Perdue's and Bell & Evans' relative success, we asked those companies as well as Tyson and Foster Farms whether they have added any food-safety measures in the past few years. We didn't reveal our test results.
Bruce Stewart-Brown, Perdue's vice president of food safety and quality, and a doctor of veterinary medicine, told us the company has increased its salmonella vaccinations over the past few years. That's designed to prevent chicks from picking up the bacterium from their mothers. Further protections, Stewart-Brown said, include an "all-in, all-out production model." Translation: Flocks are cleared out completely. Between flocks, farmers dry the empty chicken houses (which kills bacteria) and often use a product that temporarily changes the pH of the ground (to make it inhospitable to bacterial growth). Birds on each farm are the same age, so there are no older birds to contaminate newly arrived younger ones. "We also work closely with the farmers that raise our poultry," he said. "We make sure they isolate any other species of animals that might transfer microbiology to our chickens, use footwear and clothing control programs, and closely regulate visitation by outsiders."
Stewart-Brown also says that Perdue has implemented 25 food-safety steps at its processing plants.
Tom Stone, director of marketing at Bell & Evans, which produced those clean chickens, said the company has started packaging its products with a machine that seals the edges with film and shrinks the material, so there's no need for a "diaper" under the chicken to sop up fluids. "Our chickens are air-chilled and carry the ‘No Retained Water' statement," he said.
But listen to Foster Farms and Tyson and you'd think they would have been as clean. Robert O'Connor, vice president of technical services at Foster Farms and a doctor of veterinary medicine, cited the company's use of "the most technologically advanced and proven systems available." Tyson spokesman Gary Mickelson said his company's safeguards include keeping hatcheries sanitized, vaccinating some breeder stock against salmonella, and ensuring proper refrigeration during product delivery.
Our own experts say that controlling the spread of bacteria is a matter of being vigilant and taking many small steps, from hatchery to store, rather than relying on one magic bullet. A May 2008 release of USDA compliance guidelines for the poultry industry recommends 37 "best practices," including controlling litter moisture in chicken houses and continuously rinsing carcasses and equipment in processing plants. Chicken producers that follow good practices in the hatchery and on the farm and abide by those government guidelines should be able to produce fewer chickens that harbor salmonella, though not necessarily campylobacter.