If you make filter coffee at home, there is a small decision to make once the last cup has been poured: what do you do with the used coffee grounds and the filter paper?

The obvious answer might seem to be “put them in the compost”. And, in the case of a conventional paper coffee filter filled with used coffee grounds, that is a perfectly sensible thing to do at home.

But words such as biodegradable, compostable, home compostable and industrially compostable are often used as though they all mean the same thing.

They don't.

So, what is actually happening when you put a used paper coffee filter onto the compost heap?

Biodegradable and compostable are not quite the same thing

Something is biodegradable if microorganisms can gradually break it down into simpler natural substances.

That definition on its own, however, does not tell us how quickly this will happen or under what conditions.

A material might break down relatively quickly in a warm, moist and active compost heap, but much more slowly somewhere cold, dry or lacking the right microorganisms.

Temperature, moisture, oxygen and microbial activity all make a difference.

Composting is more specific. It is the controlled biological breakdown of organic material to produce compost.

Put simply:

Biodegradable describes what a material is capable of doing. Composting describes a particular environment in which that breakdown can take place.

What about home composting?

A home compost heap is a living ecosystem.

Bacteria, fungi and other organisms gradually break down kitchen and garden waste, eventually producing the dark, crumbly material we recognise as compost.

Coffee grounds are commonly added to home compost, along with paper and cardboard in sensible quantities.

A used paper coffee filter therefore contains a useful combination of materials: coffee grounds together with a small amount of paper fibre.

For this reason, used paper coffee filters and their contents can be added to a normal home compost heap.

There is, however, no reliable countdown for how long an individual coffee filter will take to disappear.

A warm, moist and regularly turned compost heap will work much faster than a cold or dry heap that is rarely disturbed.

Thin, wet filter paper will gradually soften, tear and become incorporated into the surrounding compost as microorganisms break down its cellulose fibres.

The coffee grounds will decompose alongside it.

Rather than claiming that a coffee filter will completely disappear within a particular number of days or weeks, it is more accurate to say:

Used paper coffee filters and their coffee grounds can be added to a well-managed home compost heap, where they will gradually break down with the other organic material.

Tearing the filter into smaller pieces before adding it can increase the surface area available to microorganisms, although with thin coffee filter paper this is not normally necessary.

Home composting and industrial composting are different

Commercial composting is a more controlled process than composting in the garden.

Industrial composting facilities can maintain higher and more consistent temperatures, control moisture levels and provide the aeration required for rapid biological breakdown.

A home compost heap is much more variable.

This distinction is particularly important when discussing materials that are specifically described as industrially compostable.

A product designed to break down under industrial composting conditions may require sustained temperatures and carefully controlled conditions that are unlikely to be achieved in an ordinary garden compost bin.

Something being industrially compostable therefore does not automatically mean that it is suitable for home composting.

Traditional paper coffee filters are rather different from many newer compostable packaging materials because their principal structure is made from cellulose fibre rather than a compostable plastic polymer.

What are our cone-shaped coffee filter papers made from?

Our traditional cone-shaped coffee filter papers are manufactured in Europe from specialist coffee filter paper made predominantly from fresh wood-fibre cellulose.

Cellulose is the natural structural material found in the cell walls of plants and is also the principal component of ordinary paper.

The paper is designed specifically for coffee filtration. It needs to allow brewed coffee to pass through at the correct rate while retaining coffee grounds and remaining strong when saturated with hot water.

A very small quantity of wet-strength material may therefore be used during paper manufacture to help the filter retain its structure while brewing.

This is why it would be misleading to describe a coffee filter simply as “100% wood pulp and nothing else”.

Nevertheless, the overwhelming majority of the material is cellulose-based paper fibre.

What about the seam?

If you look closely at one of our cone-shaped filters, you will notice a compressed seam running along the edge and base.

This can sometimes look as though two pieces of paper have been glued together.

In fact, this type of filter is produced using a mechanically formed seam during the converting process. The paper is pressed together to create a strong joint capable of remaining intact once the filter becomes saturated with hot water.

There is therefore no thick layer of plastic laminate or similar material holding the cone together.

Once used, the filter behaves much more like an ordinary piece of wet paper in a compost heap.

Compostable does not always mean certified compostable

This is another distinction worth making.

A material can be capable of breaking down in compost without the finished retail product necessarily carrying a formal compostability certification mark.

Certification schemes exist to test products against defined conditions and standards. Those certifications can also involve licensing rules governing who may display a particular logo on their packaging.

For that reason, we prefer to distinguish between the practical question:

“Can I put this used paper coffee filter in my compost heap?”

and the separate question:

“Does the retail product carry a particular compostability certification logo?”

They are not the same thing.

For our European-made cone-shaped paper filters, the practical answer to the first question is straightforward.

So, can I compost my used coffee filter?

Yes.

Once your coffee has been brewed and the filter has cooled, the used paper filter and the coffee grounds can be added together to a normal home compost heap.

There is no need to scrape the coffee grounds out first.

The coffee contributes organic material while the paper contributes cellulose fibre.

As with all home composting, the rate at which everything breaks down will depend on the conditions in your compost heap, including moisture, temperature, oxygen and the balance of different materials.

The filter will gradually soften and break apart as the cellulose fibres are attacked by microorganisms.

What about my council food-waste collection?

This is slightly different.

Food waste collected by councils may be treated in different ways depending on the local authority and its waste contractor.

Some food waste is commercially composted, while much of it is treated using anaerobic digestion.

Anaerobic digestion uses microorganisms to break down food waste in the absence of oxygen, producing biogas and a nutrient-rich material known as digestate.

Because different treatment facilities accept different materials, you should always follow the instructions provided by your local council.

If your council says that paper coffee filters can be placed in the food-waste caddy, the used filter and coffee grounds can go in together.

If your local authority accepts coffee grounds but specifically excludes paper, simply empty the grounds into the food-waste container and dispose of the filter according to its guidance.

Local collection rules should always take precedence.

And what does “biodegradable” really tell us?

Not as much as you might think.

Paper made predominantly from cellulose is biodegradable because microorganisms are capable of breaking down cellulose.

But saying that something is biodegradable does not tell you how quickly it will break down, where it should be disposed of or whether it is accepted by your local waste system.

That is why we think the practical question is more useful.

Instead of asking only:

“Is this biodegradable?”

ask:

“What should I actually do with it once I've finished using it?”

For a used paper coffee filter at home, one of the simplest answers is to put the filter and the coffee grounds together on the compost heap.

The coffee has been brewed, the grounds have done their job, and the paper can begin its next one.

There really are good grounds for composting.