Cans Nearly Invulnerable, Experts Say

Every year, soft-drink manufacturers and brewers fill more than 95 billion metal cans in a rattling, high-speed, mechanical conga line. At the average Pepsi-Cola plant, 2,000 cans every minute speed single-file along an enclosed conveyor line to be filled with the cola company’s most profitable product.

The aluminum cans, which account for more than half the cost of every soft drink, have become the object of a national consumer scare.

So far, people in more than 20 states--the latest being California--say they have found hypodermic needles and syringes in Pepsi cans, but independent engineering experts and company officials say it is virtually impossible for any foreign object to get into a soft-drink can or a beer can.

“I think it would be impossible to slip anything into a can, as I know something about the process,” said engineering expert Henry Paxton at Carnegie Mellon University in Pittsburgh, Pa. Paxton is a former vice president of research for U.S. Steel Corp. “The cans are basically untouched by hand as they go through the bottling plant.

“Even if you had a malingerer in the plant who slipped something into a can, I’m not sure it wouldn’t be detected,” he said. As they speed through the plant, the cans are held in place by vacuum suction, turned on their sides and flipped upside down. “I don’t think you could load something in,” he said.

“It is a real engineering trick to make these items and at that high speed, with that precision,” Paxton said. “It is one of the unsung-hero stories of engineering.”

Normally cautious about revealing details of their manufacturing operations, Pepsi-Cola engineers were eager Wednesday to explain how the company bottles its soft drinks.

Unlike some companies, Pepsi does not manufacture its cans. It buys the 20 million cans it uses a day from a variety of companies around the country, which deliver the topless, empty containers to bottling plants on pallets of about 340 cases each.

Only six companies, with 20 plants, manufacture cans in the United States, according to Jesse Meyers, who publishes the industry newsletter Beverage Digest. Before being shipped, the cans go through three inspections.

Once they arrive at the bottling plant, the cans are mechanically loaded onto an enclosed, high-volume conveyor belt.

“From that point, the cans move down the production line and they go through a rinser, turned upside down and sprayed with treated, chemically balanced water. Anything in a can would fall out then,” said Philip Faxlanger, director of Pepsi’s rapid-response bottler support group in New York. “A syringe or a pencil or something like would immediately fall out. It would be sprayed out as well. “

Each can stays upside down for up to 10 seconds and is sprayed with high-pressure water from six nozzles. Then it is flipped right-side up and moved under a spigot in an enclosed chamber, where it is filled with cola in about five seconds. The filled, open can emerges and moves to a “seamer,” which clamps on the pop-top lid, sealing the can, Faxlanger said.

“The lid itself is solid until you actually pop it,” Paxton said. “It is a very clever design. The whole can is really a superb engineering system.”

Pepsi engineers said that a syringe is too large to get into a can during the filling process because the liquid is filtered through a series of fine mesh screens to keep out debris and the tube is too narrow. The holes in the nozzles that fill the cans are about one-quarter inch in diameter.

Beer brewers take the extra step of filling their cans inside a sealed chamber flooded with nitrogen so no oxygen can get in and spoil the taste of the beer.

A filled and sealed aluminum can is, in effect, a metal balloon that takes its strength as much from the pressure of the carbonated liquid inside it as from the inherent stiffness of its thin metal sides. And, as with any pressurized balloon, any hole would cause a leak easily detected by an inspector who would then reject the can.

Pepsi officials said the company uses only new cans. Although aluminum cans are recycled routinely, they are melted down and the metal is recast for a variety of uses, including another generation of soda cans, Faxlanger said.

“If there is a saboteur, anything is possible,” Meyers said. “Somebody could have glued something inside a can so that it would not show up on the tests. But it is all hypothetical. We don’t know beans at the moment.”

The Pepsi Canning Process

Pepsi purchases its cans from outside manufacturers. Before being filled with cola, the cans are inspected, turned upside down and washed. The production line moves at a speed of 2,000 cans a minute.

New cans enter facility lined up for production.

Held in place by vacuum, cans are transferred to covered conveyor belt and inspected inside.

Cans are turned upside down for five to 10 seconds and rinsed.

Less than one second later, cans enter sealed filling machine on rotating table and are filled from spigots. (Cans are inside the machine for three to five seconds.)

Cans move onto conveyor belt again. Tops are applied and sealed.