Matavfall (food waste): sort it correctly and understand why it is collected

Food waste is wet, heavy and full of energy and nutrients. If it is burnt with residual waste, energy from the incineration process is first spent boiling away the water — a poor use of energy. When it is separated instead, both the energy and nutrients return to the cycle, while the residual-waste bin becomes lighter, drier and less smelly.

Sweden aims to collect all food waste for biological treatment, and in practice almost every municipality now collects matavfall (food waste). Houses usually have a dedicated bin or compartment, while flats use a food-waste bin in the refuse room or recycling building. Leftover food is therefore a raw material, not rubbish. Swedish households are also gradually reducing food waste. Eating the food is of course the best option, but peelings, bones and grounds must always be separated.

Most collected food waste goes to a biogas plant. There it is broken down without oxygen in large tanks, producing two products. The first is biogas, which is upgraded to replace natural gas and fossil fuels. It powers city buses, refuse lorries and cars, and is one of Sweden's most tangible climate benefits from waste management.

The second product is biogödsel (biofertiliser), a nutrient-rich fertiliser returned to farmland in place of artificial fertiliser. The phosphorus in your potato peelings therefore becomes next year's crops. This double benefit — renewable energy and plant nutrients returned to the soil — is precisely what makes food waste so important. Some municipalities compost food waste instead and use the compost in parks, but the principle is the same: the nutrients should return to the soil.

The bag you should use is determined by the facility that receives your municipality's food waste, which is why neighbouring municipalities have different rules. There are two main systems:

• Paper bag: a green or brown bag made of wet-strength paper, filled while held in a steel or plastic holder. The bag is digested or composted with its contents. It works best when filled about two-thirds full and not packed too tightly.
• Plastic bag: often green or in the municipality's chosen colour, tied closed and put in the food-waste bin. At the facility, machines open the bags and separate the plastic before anaerobic digestion.

The same rule applies to both systems: never use ordinary carrier bags or freezer bags. They are not part of the system and interfere with treatment. The municipality provides the correct bags, often free or for a small charge through bin deliveries or at municipal collection points. If you are running out, contact the municipality. It would rather give you more bags than have food waste put in the wrong place.

Smells and fruit flies arise from two things: moisture and heat. Simple habits help with both. Put newspaper or a paper towel in the bottom of the bag to absorb liquid, and allow particularly wet material such as coffee grounds to drain in the sink first. Fill the bag without compressing it and change it every two or three days. A half-full bag changed frequently smells less than an overfilled one left for a week.

Keep bins and holders in the shade in summer and keep the lid closed; flies can lay eggs only where they can reach the waste. Rinse the large bin after collection and allow it to dry, and consider sprinkling a little bicarbonate of soda in the bottom to reduce smells. Winter brings the opposite problem: wet food waste can freeze to the bin. Put newspaper in the bottom and make sure the lid will open on collection day, as the driver may leave a bin that cannot be emptied. To ensure you never miss the collection, BinMinder sends a free reminder the evening before.

The rule is that anything edible, raw or cooked, belongs in the food-waste bag: peelings, bones, fish scraps, coffee grounds, tea bags, bread and leftover food. A few things must be kept out:

• Candle wax and tealight holders: wax interferes with anaerobic digestion; tealight remains should be sorted as metal or residual waste.
• Cat litter, animal bedding and dog-waste bags: these belong in residual waste even though they may seem natural.
• Potting compost and potted plants: too much soil weighs down the treatment process; take larger amounts to the återvinningscentral recycling centre as garden waste.
• Ash, cigarettes and cotton buds: always residual waste.
• Commercial cooking fat and frying oil: never pour oil into the sink or food waste. Allow fat in a frying pan to solidify and wipe it out with kitchen paper; take larger amounts away as hazardous waste.

If you are unsure about a particular item, follow your municipality's collection calendar or sorting guide. Sorting correctly benefits both your bin and the climate.