The Shocking Science of Tender Poultry

Just over 24 years ago, I wrote a news note on Australian experiments using low-voltage electricity to stimulate beef muscles after slaughter. Data had indicated that applying up to a 110-volt current for 90 seconds to fresh, uncut carcasses would keep the muscle from tightening–and toughening–during subsequent refrigerated storage, even if removed from the bone.

Interest in this development was immediate. Within the next few weeks, three Science News readers called to note that they were preparing to slaughter a few head of cattle and could I pass along the pertinent details. As the daughter of an electrician, I had too much respect for live currents to risk providing instructions. Instead, I directed the readers to the scientists whom I had spoken with at the Meat Research Laboratory in Queensland.

Over the next 2 decades, I followed reports describing studies as this electrical stimulation-technology was investigated and adopted in the United States–for not only beef, but also lamb and pork.

Now, U. S. Agriculture Department scientists report adopting the concept to tenderize breast meat of mature laying hens–the proverbial tough old birds.

De-energizing the carcass

About 8 years ago, C. Eugene Lyon, J. Andra Dickens, and their colleagues at the Agricultural Research Service’s Poultry Processing and Meat Quality Research Unit in Athens, Ga., decided to test on chickens the electrical stimulation technology that had been worked out for carcasses from hoofed livestock. The previous work, focusing on the red meat of thigh and flank, strived to keep muscle from shrinking during rigor mortis.

With chickens, Lyon explains, the focus was going to be the white meat in breast muscle–a somewhat different type of tissue. Traditionally, poultry processors prevented the chicken breast from getting tough by waiting to debone the birds until they had been chilled for 4 to 6 hours or more. If cut up earlier, the muscle fibers would permanently shrink into a tougher state. However, the processors were looking for a quicker, cheaper method to keep the meat tender.

There’s also an older technology that accomplishes this. Raised on a Georgia farm, Dickens notes, “My momma used to go out and catch an old chicken–one that was maybe 3 years old.” After chopping off its head, “she’d let it flop around out in the yard until it was dead. That’s what everybody did, and the meat was always tender.”

At death, any glycogen–an energy-storing molecule–present in the muscle can still power contractions, and the taut muscles result in rigor mortis. Over time, this glycogen dissipates and the muscle relaxes.

Electrical stimulation works by prompting the muscle to sustain heavy contractions postmortem, thereby using up any glycogen and returning the muscle to a tender state, Dickens explains. In a sense, this agricultural engineer explains, electrical stimulation simulates the flopping action that had dissipated the muscle’s stored energy.

It started with broilers

Initially, the Athens scientists applied the technique to broiler chickens, the biggest component of the meat-poultry industry. Each year, U.S. processing plants slaughter more than 8 billion of these birds, producing meat valued at more than $14 billion. At slaughter, broilers may be only 6 to 7 weeks old and weigh just 3 to 5 pounds.

Roughly 5 years ago, broiler processors began introducing electrical stimulation into their plants, which may process more than 100 birds a minute, or some 200,000 per day. The carcasses are stimulated as they bleed out, so the procedure doesn’t add any processing time. It can improve tenderness by 30 to 40 percent.

By increasing the pace of rigor, electrical stimulation now enables those plants to cut their processing costs by requiring only 2 hours between the bird’s death and boning. Previously, Dickens notes, plants typically aged birds for 6 hours or more.

However, there is another large component to the poultry industry. Every year in the United States, 335 million laying hens–birds producing eggs either for consumption or as a source of all those broilers–are slaughtered when their egg production wanes. These hens may be 2 years old and weigh 8 to 14 pounds Typically, Lyon notes, breast meat from these hens has been so tough that food manufacturers have sought it only for relatively low-value uses, such as soups, pet food, or certain precooked meals. The scientists recently asked whether, with electrical stimulation, the meat from these big-breasted hens might be kept tender enough to be sold as fresh fillets in supermarkets.

And indeed, the federal scientists find, applying electrical pulses of 200-volt current to mature-hen carcasses for 60 seconds reduces the shear force of cooked breast tissue by about 50 percent. The improvement is slightly greater than in broilers, which start out more tender. The ARS scientists plan to report some of these findings later this month in Atlanta at the International Poultry Scientific Forum.

Also leads to cleaner’ birds

During some of their earlier work on adapting the technology to poultry processing, the ARS researchers observed that electrical stimulation often triggered “projectile defecation” by the carcasses. In effect, it loosened the bowels, which voided their contents. That may sound like a bad thing, certainly a foul-smelling development. In fact, Dickens notes, several poultry processors saw it as such a benefit that they installed electrical stimulators for that purpose alone.

Livestock feces spread during butchering is a leading source of meat contamination with food-poisoning bacteria. In some poultry plants, that early voiding of the bowels reduced by some 50 percent the need for costly rewashing of meat during slaughter.

Toward the future, Lyon envisions electrical stimulation being applied to chicken meat deboned before refrigeration. Ordinarily, deboning before refrigeration results in tough meat because the muscles contract. The researchers plan to investigate whether stimulation can improve tenderness in deboned meat. Such a process would eliminate the need to also cool bones, fat, and other tissue, which would cut energy costs and processing times.