Bad odours: tackling them with EM in bins, drains, the fridge and litter trays

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A kitchen bin in high summer, a smelly drain, a musty fridge, the cat's litter tray: household odours almost always have the same origin, organic remains that are breaking down badly. Effective microorganisms are often used to reduce them, by steering this breakdown towards fermentation rather than putrefaction.

They can be helpful, provided you know how they work, where they are useful and where they are no use at all. This guide takes you room by room, with the steps that really matter.

Where do bad odours come from?

When organic matter rots, that is, when it breaks down without air and without control, microorganisms produce several families of very smelly molecules:

• ammonia and amines: the sharp smell of urine, dirty litter, fish;
• sulphur compounds (hydrogen sulphide, mercaptans): rotten eggs, cabbage, sewers;
• volatile fatty acids: smells of rancidity, strong cheese, sweat.

EM are based on a simple principle: lactic acid bacteria and yeasts that ferment residues and produce acids. By making the environment acidic, they slow down rotting. Acidity has a well-known effect on ammonia and amines: in acidic conditions, these molecules turn into salts that no longer evaporate. This is why acidifying slurry is a recognised technique for reducing ammonia emissions.

For sulphurous odours, however, acidity does not help, quite the opposite: hydrogen sulphide escapes more easily from an acidic environment. According to the manufacturer, certain bacteria present in EM consume these sulphur compounds, but this has not been independently verified in household use.

Did you know?

The human nose detects hydrogen sulphide, the smell of rotten eggs, at minute concentrations. A tiny amount of rotting waste is therefore enough to make a whole room stink, hence the importance of finding the source.

Deodorising or masking: the difference

When faced with an odour, there are four ways to act, and they are not equal:

1. Remove the source: empty, wash, dry. This is always the priority, and often the only thing needed.
2. Ventilate: fresh air dilutes odours within minutes.
3. Absorb: activated charcoal, and to a lesser extent bicarbonate of soda, trap some of the odorous molecules.
4. Mask: a fragrance covers the odour without solving anything.

EM are in a category of their own. They act on the organic residues themselves, changing the way they break down. So they are a maintenance and prevention measure rather than an instant deodoriser. To work, they need to be in contact with the material and need a little moisture: sprayed into thin air or onto a dry, clean surface, they do very little.

Key points

A persistent odour almost always points to a source that needs finding. EM help keep what is fermenting or breaking down under control, but they replace neither cleaning nor ventilation.

Bins and waste containers

• Empty more often in summer, and tie bags securely.
• Drain wet waste and slip a sheet of newspaper or cardboard into the bottom of the bag to soak up liquids.
• Wash the bin regularly, then spray the inside with a 5 to 10% dilution of EM Clean, or a 1% dilution of EM-A, and leave to dry without rinsing.
• Between washes, a light spray over fresh waste limits fermentation odours.

If most of the smell comes from peelings and leftovers, the most lasting solution is to take them out of the bin. A bokashi bucket ferments them in a sealed container, with no smell of rotting: our bokashi guide explains everything. A composter or wormery that smells bad has specific causes: see our guide on diagnosing compost problems or the one on wormery odours.

Drains and pipes

A sewer smell rising from a basin or shower often has a mechanical cause, which should be checked first:

• A dry trap: in a little-used room, the water in the trap evaporates and no longer blocks the gases. Simply run the tap for a minute.
• A clogged trap: hair, soap and grease form a deposit that rots. Take it apart and clean it; it only takes five minutes.
• A blocked or missing plumbing vent: in this case, only a plumber can fix the problem.

Once the trap is clean, regularly pour the remains of your cleaning dilutions, or a little diluted EM Clean, down the drain as the manufacturer recommends, preferably in the evening so it stays in place overnight. This is a sensible maintenance use. For septic tanks, blockages and dry toilets, everything is explained in our guide Septic tanks, drains and dry toilets.

Fridge, shoes and fabrics

The fridge

A smelly fridge is almost always caused by forgotten food or a spill. Empty it, throw away anything doubtful, wash the shelves and walls with hot water and washing-up liquid, rinse and dry. Also clean the small drain hole at the back, which is often blocked. For lingering odours, a small dish of activated charcoal or bicarbonate does the job. We do not recommend spraying EM inside the fridge, on surfaces that come into contact with food.

Shoes, rugs, mattresses

Fabrics hold on to sweat and damp smells. EM Clean deodoriser is ready to use: spray it directly onto the fabric, without soaking, and leave to air-dry. For shoes, alternate between two pairs so they dry out properly between wears. For a rug or sofa, vacuum first, then follow the dilutions in our guide Natural cleaning with EM Clean.

Emy's tip

Take the insoles out of your shoes every evening and let them air-dry. A dry insole hardly smells at all: it is moisture that feeds the microorganisms responsible for the odour.

Litter trays and pet areas

Litter tray odour comes mainly from urine: within a few hours, bacteria turn urea into ammonia. Changing the litter often therefore remains the first step. In addition, the manufacturer of Microferm recommends regularly spraying the litter, tray, kennel, hutch or henhouse with a solution of 10 ml per 1 litre of water. Microferm EM-A Activated Solution contains no fragrance, which makes it the simplest choice around animals.

A few precautions:

• spray when the animal is not there, and let it dry before it returns;
• never spray a scented product directly onto an animal: cats in particular struggle to eliminate certain compounds in essential oils, which they absorb through the skin, by breathing them in or while grooming; and do not spray anything near birds, which are very sensitive to fragrances and airborne droplets;
• an unusual smell of urine or faeces, or an animal avoiding its litter tray, may signal a health problem: speak to your vet.

Advice specific to dogs, cats and small animals is gathered in our guide EM for dogs, cats and small animals.

What you can reasonably expect

Studies on EM and odours are few in number and give variable results. Above all, they show that it is lactic acidification that matters. In laboratory trials on very smelly organic waste, EM added on their own did not lower the acidity or the odours; they only worked when combined with a source of sugar, such as molasses, and ordinary lactic ferments did at least as well. In pig farming, a trial with another commercial microbial additive found no difference in odour or ammonia between treated and untreated buildings.

Our view: for small everyday odours linked to organic residues, EM are a practical and gentle aid, alongside good hygiene. They will not get rid of an odour whose source remains in place.

In summary

Household odours come from rotting organic remains: ammonia, sulphur compounds, fatty acids. Removing the source, drying and ventilating remain the essential steps. By encouraging acidic fermentation, EM mainly help against urine and ammonia-type odours, in bins, clean drains, fabrics and litter trays, provided they are in contact with the residues. For the fridge, choose washing and activated charcoal; around animals, a fragrance-free product. And if an odour persists despite everything, look for the cause: a dry trap, a blocked vent or a health problem in the animal.

Related products

EM Clean, multi-purpose EM cleaner | Classic - 2 L Bag-in-box

For home, outdoors, pets ... from 2 to 250 L

€20.39

EM Clean, EM deodoriser | Mint

Naturally neutralises bad odours

€15.89

Other topics in the guide

Vermicomposting30 sheets →Composting25 sheets →Bokashi24 sheets →