What can lead to food becoming unsafe?

This is how food spoils

Mold: Beware of poisons

The peel of an apple is a protective layer for the delicious, juicy flesh. If the fruit falls, this protective layer will be damaged. Now microorganisms such as fungal spores from the air and bacteria from the ground can penetrate and establish themselves.

Christine Langer from the Association for Nutritional Therapy and Prevention (FET) explains: "The organisms have everything they need to thrive: water, sugar and oxygen."

Good food for the microbes. Molds in particular are particularly treacherous: "Molds penetrate much deeper than the fur on the food would suggest, especially with juicy food. The invisible threads sometimes run through the entire food."

Molds also produce toxins. Aflatoxin is the most dangerous; it occurs mainly in moldy nuts and spices. Aflatoxin can damage the liver and, in the long term, promote liver cancer.

"That is why you should never store dried herbs and spices near the stove, nor should you keep seasoning them over the already steaming pan," advises nutritionist Langer.

"The water vapor condenses in the can, so the herbs or spices become moist. This creates the ideal breeding ground for mold."

If the first small mold stain appears on a firm bread crust or on the rind of hard cheese, you don't have to throw everything away immediately: "Then it can be enough to cut away the area with the mold generously."

Food cannot spoil through mold alone. There are four other types of spoilage: putrefaction, fermentation, acidification, and rancidity.

Putrefaction: Meat and fish are particularly endangered

When putrefaction, bacteria break down proteins, which is why protein-rich foods such as fish and meat are particularly susceptible. During this process, among other things, ammonia and hydrogen sulfide, which smells like rotten eggs, are produced.

In addition to the putrid smell, yellow-green discoloration and slime are also signs that the food is already rotten.

Fermentation: cider by chance

Fermentation breaks down carbohydrates with the help of wild yeast. When pressing the must, it is quite intentional, yes necessary, that yeasts divide the long starch molecules into shorter sugar chains and that some alcohol is produced in the process.

With conventional fruit juices, however, such a fermentation process literally leads to spoilage. The first clue is often some foam. The fermentation also produces the gas carbon dioxide, which also makes mineral water so tingly.

Acidification: Drink up raw milk quickly

If the milk is acidic, then you are dealing with another form of food spoilage: During acidification, lactic acid bacteria break down carbohydrates.

Depending on which strains of these lactobacteria occur in the milk, either only lactic acid or methanoic acid (colloquially formic acid), ethanoic acid (acetic acid) and butanedioic acid (succinic acid) is produced.

The acids ensure that the proteins in the milk coagulate - that's why sour milk sometimes has flakes. Incidentally, most lactic acid bacteria like it warm: below ten degrees Celsius they only multiply slowly, which is why milk and yoghurt always belong in the refrigerator.

It also makes a difference which type of milk you buy: "UHT milk is ultra-high-temperature, that is, the milk has been heated to at least 135 degrees Celsius for a few seconds. This kills almost all germs, so that the opened package becomes one Remains edible in the refrigerator for a week, "says food expert Langer.

Fresh milk was heated to around 75 degrees Celsius for up to half a minute. After this so-called pasteurization, germs remain, so fresh milk should be consumed within three to four days.

You should definitely drink raw milk very quickly: "This is untreated and therefore only lasts for a day or two."

Rancid butter, smelly salad oil

Butter and salad oil are more likely to be affected by fat spoilage - they then taste rancid. Fat molecules consist of a glycerine part to which one to three molecular chains are bound, the so-called fatty acids. The fatty acids are split off with the help of enzymes.

In addition, the fatty acid chains themselves can still be broken down. The fragments, so-called volatile ketones, are responsible for the nauseating smell.

It is important in the household: pure fats such as salad oil contain no water and only spoil by becoming rancid. In water-in-oil emulsions, on the other hand, for example in butter, bacteria, yeasts and molds can also settle.

Best before date is not the best before date

But how can you test whether food is still edible? First of all, a look at the best-before date helps: "Until this date, the manufacturer guarantees that the quality and palatability of the product are guaranteed," says Langer.

If a little water settles in a yoghurt or if the powdered chocolate pudding does not turn quite as dark brown as usual, then that does not change the palatability.

In addition: The best-before date is not an expiration date! A yogurt that has not been opened can still be edible days after the best-before date has passed.

The situation is different with the use-by date, which is written on fresh meat and fish, for example: "You really shouldn't eat the product after this date," says Langer.

Be sure: the "eye-nose-tongue check"

If you are still unsure, you should inspect the food carefully before consuming it. The Federal Ministry for Food, Agriculture and Consumer Protection speaks of the "eye-nose-tongue check".

First you should take a good look at your food: Is the mold blooming red, green and black on the cheese? The sausage is greasy and the grilled meat rather colorless? Then get rid of it!

If everything looks okay, the smell test comes: Does the oil smell rancid, the milk sour, the favorite liver sausage not as usual? Then that too ends up in the garbage immediately.

And if you are still not sure, you should try it. Christine Langer from the Association for Nutritional Therapy and Prevention: "Even if a food is spoiled, a small bite does not endanger your health."