Mould in foods – health risks and how to avoid them

Mould occurs everywhere in nature. Mould refers to fungi which form long threads known as hyphae and tiny spores only visible under a microscope. Mould uses these spores to spread through the air. If the conditions are right, mould forms a mycelium, a complex network of hyphae. Once the mould becomes visible, it often forms a powdery or fuzzy coating. Some foods offer ideal conditions for mould growth. In household contexts, these include bread, fruit, and jam. Sufficient moisture is a prerequisite for mould growth. Mould can grow on surfaces, but it can also penetrate deep into harvest products or foods and spread.

Mould spores spread through the air. If they land on a food and find suitable conditions – the right temperature, pH, and moisture level – they can settle there and begin to grow. In a warm and moist climate, carbohydrates, plant and animal fats, and protein allow for optimal growth. Suitable conditions frequently arise when foods are improperly dried, incorrectly stored, or inappropriately processed.

If mould spores land on foods and the conditions are favourable, they begin to germinate. They form filaments known as hyphae. These hyphae can spread inside the food and are thus not visible to the naked eye. Mould typically only becomes visible after some time and forms a whiteish-green, sometimes black or yellow coating. The coating generally has a powdery or fuzzy consistency.

The following tips can help to prevent mould on foods.

• Buy foods as fresh as possible and consume them quickly; avoid bulk buying.
• Store foods clean, dry, and in a cool place.
• Store foods separately from each other.
• Clean bread boxes weekly and wipe down with vinegar and water.
• Remove breadcrumbs, as these facilitate mould growth.
• Clean the refrigerator after mould is found on foods.
• Throw away mouldy foods and do not leave them open.
• Store grains and flour in a cool and dry place and shake regularly.
• Try to buy undamaged fruits and vegetables. Do not store spices for years.
• Instead, buy them in small amounts and use quickly.
• Store mould-ripened cheeses (e.g. Roquefort, Camembert) in separate containers.

Once foods have become mouldy, they should no longer be consumed nor left to stand open. Instead, they should be thrown out immediately. Moulds can form poisonous substances known as mycotoxins, which can be harmful to health. Foods particularly susceptible to mould include fruit conserves, fruit juice, jam, jelly, fruits, milk, and dairy products as well as bread. Once food has become mouldy, it should no longer be eaten. Exceptions to this rule include air-dried sausage (salami) and ham (e.g. whole Parma ham, not sliced ham). In these cases, the mouldy parts should be generously removed and not eaten. When it comes to nuts, the hazard often stems from mouldy individual nuts. Suspicious-looking nuts should therefore be discarded.

Yes. There is a group of moulds which is used in the production of certain types of cheese and salami, and which are harmless for human consumption. Examples of these types of cheese include Brie and Camembert. In order to prevent the mould from spreading to other foods in the refrigerator, these cheeses and salamis should be stored in separate packaging. 

Mould toxins, termed mycotoxins, are natural secondary metabolites produced by mould. For animals and humans, even small amounts of mycotoxins can be harmful to health. A disease caused by mycotoxins is called mycotoxicosis. More than 400 species of mould can produce over 650 mycotoxins. However, only a relatively small number of mycotoxins naturally occur frequently and in concentrations high enough to be of importance for food and feed safety. Mould spores can also contain mycotoxins. They are almost all heat and acid stable and can therefore not be removed by cooking, frying, or marinating in acid.

Mycotoxins can lead to health impairments in humans. Their toxic effect depends on the specific toxin, the duration of exposureClose dialogexposureExposureTo glossary (acute or chronic), the amount of intake, and the health condition of the individual consumer. Possible symptoms of acute mycotoxin poisoning in animals and humans include liver and kidney damage, skin and mucous membrane damage, impairment of the immune system or the central nervous system, hormone-like effects, nausea, vomiting, and diarrhoea. Additionally, chronic exposure to some mycotoxins can lead to carcinogenic and mutagenic effects.

EU regulations set maximum levels on the amount of mycotoxins permitted in certain foods, as it is unfortunately not possible to avoid them entirely. Therefore, there are maximum levels for certain mycotoxins in almonds, pistachios, and oilseeds as well as for grains and grain products. Whether additional regulations are necessary or if the existing ones are sufficient for health protection is constantly evaluated. Providing such advice is a risk management task and thus falls under the purview of the German Federal Ministry of Agriculture Food and Regional Identity (BMLEH) in Germany. Insights gained from national research projects are also examined accordingly.

In the household, moulds forming mycotoxins are frequently found on bread, yoghurt, or cheese. The food should be thrown away as soon as the mould becomes visible (see question “How should foods which are already visibly mouldy be handled?). In this way, consumers can reduce the health risks caused by mycotoxins.

Mycotoxins can also occur in processed foods, for example when contaminated, raw materials such as grains are further processed, e.g. oats to oat flakes. Consumers are generally not able to identify these contaminations. However, for many foods, EU regulations set maximum levels on the amount of mycotoxins permitted (see question: “How can consumers be protected from mould toxins?”).

A current example concerns the investigation of plant-based drinks made from grains, nuts and almonds or pulses such as soya, which are consumed as an alternative to cow's milk. The data collected to date by the German Federal Institute for Risk Assessment (BfRshort forGerman Federal Institute for Risk Assessment) and others, show that mycotoxins can be detected in plant-based drinks – as well as in the plantbased raw materials used in their production. These substances are natural toxins whose occurrence in food is undesirable but cannot be completely avoided.

The assessment of health risks was based on intake data for cow's milk. For most of the mycotoxins examined (ochratoxin A, deoxynivalenol and T-2/HT-2 toxins), the BfRshort forGerman Federal Institute for Risk Assessment considers the likelihood of health impairments due to the levels detected in plant-based drinks to be low or of little concern. With regard to the aflatoxin B1 levels detected in almond drinks, the BfRshort forGerman Federal Institute for Risk Assessment concludes that health impairments can occur in sensitive consumer groups, such as children, with a medium likelihood. The precise results and an assessment of the mycotoxin levels detected can be found in the BfR opinion.

In general, the following applies to healthy nutrition: a diverse and varied selection of foods not only ensures a balanced nutrient intake, but also helps to keep the intake of undesirable substances, which cannot always be avoided due to the natural origin of our food, as low as possible.