I visited a meat-processing factory to find out exactly how McDonald's hamburgers are made

OSI is the American company first supplied McDonald's hamburgers. You'll find few factories that are bigger, and if you do, they'll probably be in the US.

When McDonald's was starting out in Europe, OSI set up in the German village of Günzburg.

The factory isn't officially part of McDonald's, but there are important agreements between the two companies.

"About 90% of the production of this factory is for McDonald's," said Eunice Koekkoek, a McDonald's representative.

It's immediately apparent from the smell when you enter the factory that it produces masses of hamburgers — even the reception area smells of beef.

Employees who have had a stomach bug aren't allowed to work until they've investigated the cause with their doctor, in order to prevent bacteria and viruses coming into contact with the meat.

There are no preservatives in the meat, so the quality requirements that apply at the factory are very strict.

To prevent objects from ending up in the meat, nothing is allowed to go loose in the factory — that means jewelry must be removed, and plastic pens are also out of the question.

Before entering, you have to put on protective clothing and wash your hands thoroughly. As I wanted to make notes, I was given a clipboard and a pen. They were both made of metal because in the final phase of the production process the burgers go through a metal detector — so if that pen were to end up in the meat, it wouldn't go unnoticed.

At the factory, it's mainly large pieces of meat coming in. McDonald's requests this from slaughterhouses, as larger pieces of meat reduce the risk of contamination because they have a smaller surface area that could be contaminated by bacteria.

This space is filled to the brim with these kinds of containers, yet all that meat is processed within a day.

Forklift trucks are constantly driving to and fro to collect new containers of meat.

Almost 500 containers a day are needed to make enough burgers, so a lot of work is required to get them to the right place on time.

While the blenders grind the meat, the machine ensures that any small pieces of bone are eliminated.

A total of eight containers of meat weighing 500 kilograms each (that's 40 to 50 cows) can be processed at the same time — so if you eat a McDonald's hamburger, it's actually not from one cow, but dozens.

The minced meat ends up in a separate container to be used for the burgers.

Only when the minced meat looks like spaghetti is it perfect.

A mix of fresh and frozen beef means the burgers can be brought to the correct temperature more quickly. That way, they also hold their shape more easily — there's no binding agent in the meat.

These machines can also produce vegetarian burgers. "This has even been done here for another McDonald's country," Koekkoek said.

Right now, the factory is seeing an increase in production. But should the demand for meat decrease in the future, OSI could easily turn over its earnings model, it said.

Ice forms on the machines, and water vapor in the air condenses.

Fewer people than you might imagine are required to keep the production process going.

A total of 200 people work at the factory, but about 45 to 60 people are present per shift.

The factory can make about 30 million hamburgers a week — its actual output is just slightly below that at the moment.

McDonald's and OSI normally don't use this full capacity, mostly to ensure they can use the extra in case demand suddenly increases.

For McDonald's hamburgers, the fat content has to be 20%. For comparison, minced beef available in supermarkets can contain a maximum of 25% fat.

Hamburgers at the factory are grilled and tasted to see whether the taste, structure, and texture are up to McDonald's standards.

To grill the burgers, the factory has an exact replica of the kitchen you'd find in a McDonald's outlet. It's essential for food safety that the burgers reach a temperature of at least 69 degrees Celsius (156 degrees Fahrenheit). That's why a burger at McDonald's can never be cooked "medium rare."

One of the 40 quality checks is a metal detector. No plastic objects are allowed in the factory — so if an employee needs a pen, for example, it must be made of metal. That's so that any loose objects in the factory that accidentally end up in the burgers will be immediately noticeable before they leave.

If a customer complains that they've found something in their burger, McDonald's first question is where and when the burger was bought.

"We first check whether we've received similar complaints within the same time frame at the same location, and we investigate what may have happened during the production process," Koekkoek said.

"After this investigation, the complaint is often resolved. Due to numerous quality checks at OSI, it's almost impossible for anything to turn up in the meat. In the event of a serious complaint regarding food safety, we immediately examine the entire chain — but that rarely happens."

The boxes show exactly when a burger was produced, where the meat came from, and where the burgers are headed. So if there's something wrong with the meat, it's easy for McDonald's to know within a few hours which slaughterhouse and farm the meat came from.

Because cows are registered at birth, everything that happens to them is recorded, and every change of owner is registered. Using a special code on the box, you can even find the exact cow the meat came from.

"We make sure cows are always slaughtered in their country of origin," Koekkoek said, "so they don't need to be transported far."

For German hamburgers, 60% of the beef comes from Germany, 35% is Dutch, and 5% is from Poland.

"In the Netherlands, for example, we don't supply enough beef to produce hamburgers that are purely Dutch," Koekkoek said. "That's why we use some meat from Germany and Poland. But if we use the word 'Dutch' in a name for a limited-edition burger like the Dutch Deluxe, for example, we guarantee that all the meat comes from the Netherlands."

The meat used for the hamburgers complies with European and national standards, McDonald's said.

"We take animal welfare into account, but we can't decide on our own to switch to organic meat, for example," Koekkoek said. "That said, every step McDonald's takes towards sustainability has a huge impact on the 37,000 restaurants we have around the world."

Before the boxes disappear, another sticker is placed on them saying where the burgers came from and where they're going.

On the same industrial estate, you'll also find the factory where the buns for Germany's hamburgers are made.

The village of Günzburg is an important area for McDonald's.

The burgers remain at -18 degrees Celsius until they're unpacked in the restaurant.

A hamburger is typically on your plate within three weeks of the cow's slaughter, McDonald's said.

Koekkoek said it was largely a myth that McDonald's burgers taste different all over the world.

"The meat, of course, derives from cows from all over the world, and real connoisseurs will taste that difference," Koekkoek said. "But the consumer is unlikely to be able to taste the difference in the beef's origin, due to the other flavors of the burger bun and the sauce."

Koekkoek added: "That said, the taste experience of hamburgers all over the world may be slightly different because of the amount of salt and pepper used — some countries like more salt than others. But that's the only difference, apart from the origin of the beef."