Can You Compost Moldy Food and Rotten Fruit?

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We all LOVE fruit. It’s the most primordial and instinctively delicious food there is. Like most people, I’ve been guilty of leaving it out on the counter one too many days, only to find it moldy and swarming with fruit flies! Honestly, I hate to admit it, but I’ve even had similar experiences with moldy bread and other foods! What now? 

You can probably guess it, compost time!

Rotten Fruit is a perfectly fine compost material and it usually serves as a nutrient-rich source of nitrogen and other important plant nutrients. While a couple of rotten bananas or a moldy orange are no big deal, there are some considerations to take into account if you plan to compost large quantities of fruit.

When it comes to composting other foods it is generally okay but there are certain things like meat and other oily foods you must completely avoid! One of the biggest issues associated with composting some foods is the animal pests they may attract.

How To Know If Moldy Food Is Okay To Compost

The definition of rotting means to be undergoing an unfavorable decomposition process. Favorable decomposition would be like in the case of fermented foods,  beverages, or when making compost.  Identifying when your fruit has started undergoing this process is easily observed through the senses of sight, touch, and smell.

The first clue is the sight! If you see strangely colored or fuzzy molds covering your fruit then you know it might have some secondary growth. While most molds are harmless, others can produce secondary metabolites that may cause irritation and digestive discomforts. The common powdery green mold you see on many fruits is a species known as Penicillium, from which “Penicillin” the antibiotic was originally synthesized. It is also a healthy member of your composts food web!

If there’s nothing visually wrong with it then give it a whiff. The smell is oftentimes the best indicator of microbial growth.  Sour smells likely indicate lactic acid bacterias, another beneficial microbe for your compost. If your fruit smells like something you’d order at a bar then it’s probably being consumed by alcohol-producing yeast. Left any longer they will start to smell like vinegar. While these aren’t particularly harmful organisms there may be other less-beneficial organisms that could cause digestive issues if consumed.

Be Aware: Rotten Foods Could Be Harmful To Your Health

While many of the organisms we see on rotting food may not be directly harmful to our health, they are indicators that there is an uncontrolled growth of microorganisms. This could contain microorganisms that cause infections or make us sick for a variety of reasons. This is why many of us still have the instinctual reaction to be completely grossed out by rotting foods! It is best to avoid eating these foods if we have a feeling they might not be right for consumption. It’s best to trust your instinct on this one!

If your food is starting to rot, it means the decomposition process is already underway! Adding it to your compost pile will accelerate the decomposition process, just make sure you follow all the composting best practices to ensure you’ll produce high-quality compost!

Common Problems With Composting Moldy Food

Ants – While Ants aren’t necessarily harmful to your pile, they are a nuisance and can be difficult to work with. They are often attracted to sweet things like fruit so if this is an issue in your area be sure to take precautions. Mix your rotting fruit well with other materials or hide in the center of your pile to make it less accessible and attractive to ants.

Fruit Flies – Fruit flies don’t consume your food directly but rather feed on the nutrient-rich yeasts that are breaking down things like fruit. It’s extremely common to see these in your compost pile but they don’t have any direct negative impacts. They can be annoying, particularly if you have an indoor composting system. Covering the surface of the fruit with other materials is usually enough to keep them at bay.

Excessive Moisture – Fruit and other foods are mostly water so consider this when mixing it into your pile. If adding a lot of food or fruit it’s good to add a highly absorbent carbon-rich material that will help balance out the moisture and prevent anaerobic conditions. Mixing your pile well will also ensure that there is not an excessive accumulation of moisture in a specific location within your pile. 

Excessive Nutrients – Foods are relatively nutrient-rich materials which could disbalance your carbon-nitrogen ratio. Just like with the moisture, it’s good to balance this with a carbon-rich material when adding large quantities to your compost. 

House Flies – While this shouldn’t be an issue if compost is properly maintained, the production of houseflies on rotten foods is not uncommon. If you see maggots consuming your rotten food then it’s likely the larva of house flies! They actually will help break down the compost but will be a nuisance and could spread disease. If you have larva try flipping your compost or adding finely broken down materials to try and heat your pile.

Fruit Peels and Other Slow to Decompose Items – There’s no doubt about it, some things just take longer to decompose.  Many fruit peels, like those of citrus, take much longer to decompose than the rest of the fruit. In small quantities, it doesn’t matter since you can always separate them later, but if you plan to compost large quantities of rotten oranges (or other difficult to decompose fruits) you should consider this!

Acidity – Many foods are naturally acidic. While acidic foods won’t usually have a huge impact on the final pH of your compost, large quantities of acidic fruits may acidify your pile if not properly tended. While this will generally be remediated in the composting process, adding enough ashes to cover the food should help balance any unwanted acidity.  Also make sure your pile does not go anaerobic, because fruit sugars tend to naturally become acidic in the absence of oxygen!

Large Pests and Rodents – Many other rodents and noxious animals love the food we eat, and usually aren’t as picky as us! If you have issues with mice, raccoons, or other animals then you probably want to take precautions to deter them from your pile. Usually mixing it with manure and other organic substances makes it less pleasurable. Rodents are particularly attracted to different types of grains we consume like rice, corn, or wheat. 

Small Pieces for Quicker Decomposition – If you’re throwing whole fruits or large pieces of food into your compost, consider breaking them down a bit first. This will ensure that they break down quicker and reduce any potential issues. You can do this with your shovel, machete, blender, or whatever tool you want! The smaller the pieces the better.

Avoid Oily Foods – Oils are not beneficial for your compost! In small quantities they are harmful but pouring out old frying oil into your compost is not the best idea. In some cases, it can create conditions that resemble anaerobic conditions and harm the beneficial microorganisms in your compost. 

Could I Compost Rotten Food Waste on a Large Scale?

Food waste is HUGE for most fruit and vegetable vendors throughout the world. As a matter of fact, about 50% of the fruit and vegetables that are produced commercially in the USA goes to waste! For this reason, I’ve known many people who take advantage of this to get primary materials for composting. You can ask local fruit vendors or grocery stores and they might let you take their waste! Oftentimes large corporate businesses will deny you, possibly for legal reasons or because they already supply it to another person. Just make sure you express that you are not collecting it for human consumption (even though a lot of the food is actually perfectly fine!).

Most people who do this will usually feed these leftover foods to animals like pigs or chickens and then use what’s left for the composting process. These leftovers get mixed with manure and a carbon rich material to be converted into compost! This can be a great system if you have a good source for wasted fruits and vegetables and need lots of high quality compost!

Don’t let that mold go to waste!

There is no need for old food to end up in the landfill. When foods end up in the landfill they can contribute to the contamination of soil and underground water supplies. Anaerobic decomposition taking place within the landfill will also create high quantities of greenhouse gas emissions. Compost when you can!

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