Question:
There are often spots of blue mould on older cheeses, though it does not completely cover the cheese. I usually scrape it off or occasionally cut it off. Is this necessary or is it okay to eat?
Answer:
Given the constant increases in food prices, reducing food waste is a simple step that can help with efforts to make the most of a food budget. New Zealand households waste about $1520 of food yearly, meaning about $30 is thrown in the rubbish bin every week. Topping the food waste list are rotten vegetables and mouldy bread, but given the high price of cheese, the question of what to do with mouldy cheese is relevant.
Certain moulds and mould toxins can cause significant health problems. Mould that forms unintentionally on foods is quite different to the purposeful moulds used in the production of products such as blue cheese. Moulds used in food production either aren’t capable of producing harmful toxins or have been grown in a controlled environment to obtain a strain that doesn’t produce harmful toxins. So, a bit of tasty blue cheese is quite different from a piece of mouldy bread containing harmful mycotoxins. Every effort should be taken to reduce mould formation and to avoid eating mouldy foods.
Moulds are microscopic fungi that can grow on our food or any plant or animal matter. Most moulds are made of threadlike filaments that are often easily seen. These structures of fungi behave like branches and roots and the roots can potentially grow deep into your food. Although you may see only a tiny circle of mould on the surface, the roots can penetrate deep into the food, potentially releasing poisonous substances around those threads. Cutting visible mould from food does not necessarily remove the mould infestation and its inherent health risks.
Fungi also produce spores, which can be transported by air, water or insects, and allow the fungi to spread.
From a health perspective, moulds are an issue because certain ones can cause allergic reactions and respiratory problems. Others can produce mycotoxins, poisonous substances that make us sick.
Humans have a very competent system for destroying unwanted micro-organisms and removing toxins, but if sufficient doses of toxins are eaten, they can overwhelm this highly efficient system and cause serious problems. Some mycotoxins produced by fungi can cause nausea, vomiting and, in exceptional cases, cancer and death.
Aflatoxin is an example of a toxic substance produced by common moulds Aspergillus flavus and Aspergillus parasiticus. The International Agency for Research on Cancer classifies aflatoxins as a Group 1 human carcinogen, placing them in the same cancer-causing category as alcohol and tobacco. There is no safe aflatoxin intake level, so every effort is made to minimise the contamination of human and animal food supplies.
A small proportion of moulds that grow on cheeses stored in home refrigerators were of the genus Aspergillus, and a subset of these was capable of producing aflatoxins. Between 0.3-8% of moulds on cheeses may be capable of producing harmful aflatoxins.
Soft cheeses, such as feta, with visible mould are best discarded as they can be significantly contaminated below the surface. Harder cheeses may be salvageable by cutting off the mould and at least another 2cm of cheese below and around the mould. Other hard foods such as pumpkin, carrots and cabbage may also be salvageable by cutting off at least 1-2cm around where the mould was.
But other soft and porous foods, such as other dairy products and breads, should be thrown out if they have visible mould. Even if only one slice of bread has visible mould, the entire loaf should be thrown out because invisible mould spores could be present throughout the remaining loaf.
Tips to Reduce Mould Growth
- Keep foods covered when serving them, to prevent airborne mould spores from contaminating food.
- Do not store half-used cans of food in the fridge; empty contents immediately into a clean storage container before refrigerating promptly.
- Do not leave perishable items uncovered in the fridge (cover with wrap).
- Do not leave perishable items outside the fridge for more than two hours.
- Eat leftovers within two days, so mould doesn’t have a chance to grow.
- Given our humid climate, store bread in the fridge or freezer to reduce mould formation. Ditto for other perishable items.
- Keep dry goods such as cereals and biscuits in airtight containers or sealed tightly in packaging.
- Ensure vegetables are ventilated during storage and do not sweat.
