McDonald's answers 'Why doesn't your food rot?'

Start typing "McDonald's burger" into Google's search engine and a burger from the Clinton administration will show up.

Posts more than a decade after the purchase shows the 1996 burger still looking remarkably similar. This burger and other experiments involving the fast-food giant's fare have sparked something of an urban myth about McDonald's food—mainly that it doesn't rot.

In a series of posts on its website, McDonald's answers customers' frequently asked questions about its food in the U.S., including "Why doesn't your food rot?"

Read MoreWhy fast food doesn't look like the ads

The answer? "In the right environment, our burgers, fries and other menu items could decompose," McDonald's maintains.

The company goes on to detail just what kind of environment food needs to rot:

"The reason our food may appear not to decompose comes down to a matter of simple science. In order for decomposition to occur, you need certain conditions—specifically moisture. Without sufficient moisture—either in the food itself or the environment—bacteria and mold may not grow and therefore, decomposition is unlikely. So if food is or becomes dry enough, it is unlikely to grow mold or bacteria or decompose. Food prepared at home that is left to dehydrate could see similar results."

The post appears amid increased emphasis from McDonald's about the quality of its ingredients. On its recent earnings call, CEO Don Thompson stressed that it has "freshly prepared products."

McDonald's employee site bashes fast food
McDonald's employee site bashes fast food

"Every morning, as I mentioned, we actually crack eggs. We cook in our restaurants. This is not a microwave deal. We actually cook. We have grills and fryers and ovens," Thompson told analysts.

In an email, McDonald's spokeswoman Lisa McComb said the company recently refreshened the food section of its site to address the top questions it receives.

For those interested in learning more about the McDonald's supply chain, Mickey D's also addresses other vexing customer questions including "What is in a Chicken Nugget?" and "Are your burgers made using real beef?" Click here to see more.

—By CNBC's Katie Little