In the recycling rules for my community, there is an instruction to thoroughly wash all glass, plastic, and metal containers before depositing them into the recycle bin for collection.

Is this step really necessary for the recycling process to occur (or occur without delay)? I've heard that recycling facilities already wash all glass, plastic, and metal material using very effective methods anyhow; why then would the items need to be washed twice?

  • Obsolete and chatty comments cleaned-up.
    – Oddthinking
    Jun 17, 2013 at 15:32
  • @Oddthinking, Please link to a dump instead of deleting them outright. Example: islam.stackexchange.com/questions/2949/…
    – Pacerier
    Jun 10, 2015 at 6:21
  • 2
    @Pacerier: Sure. Here is my summary. Some comments were obsolete and therefore no longer relevant to improving the question. Some comments were chatty, and therefore never relevant.to improving the question. None were worth saving.
    – Oddthinking
    Jul 8, 2015 at 23:47

3 Answers 3


Here are comments from two of the major recyclers in Australia:

From VISY:

To rinse or not?

Ever feel like you are wasting a ton of water while rinsing out your recyclables? According to VISY, it is not necessary to rinse out containers, but you do need to make sure all food scraps are removed.

From SITA who recently took over WSN:

Rinse the containers to make sure they are clean and won't attract pests.

From Planet Ark (respected environmental group)

One of the most common questions about recycling is how clean do jars, cans and pizza boxes need to be before they can go in the recycling bin.

Small amounts of food left don’t interfere with the glass and steel recycling process. Scrape all the solid food scraps out of jars and cans and then put them in the recycling bin. If you’re concerned about having left over food in the bin you can lightly rinse out your jars and cans. Using left over washing up or rinsing water is best as there’s no point wasting good water just to wash recycling.

Looking at the different methods of processing:


Heating the aluminium to a temperature of 700°C changes it into a liquid state. It is then cast into ingots, ready for delivery to rolling mills where they are milled and remade into new products.


The single-colour cullet is put onto a conveyor belt and goes through a special process called beneficiation, which removes contamination such as bottle tops, metals, ceramics and labels. The cullet is then crushed and sent to a glass furnace where it is added to the mix.


The plastics are either shredded, chopped or ground and then washed to remove further contaminants. The plastic is melted and pushed through an extruder, a bit like an old fashioned mincer or a spaghetti maker. It is then cooled and pressed through a die and chopped or pelletised into granules. It is then ready to be made into new products.

It would appear that neither bugs nor food scraps would put a spanner in the works. I assume there would also be some sort of prewash before it got to that stage.

It appears that a thorough rinse would be a hygiene thing for your own garbage bin, but not going to affect the process. However it is necessary to remove solid food object.


A 2009 Slate magazine article tackles this question:

Once you put your recyclables on the curb, they aren't processed right away. [...] Now imagine your bottle of half-eaten, four-month-old tartar sauce, lounging about in a stuffy warehouse and getting riper by the day. Not pleasant, is it?

The author, Nina Shen Rastogi, goes on to quote an unreferenced anecdote about an anonymous person's mother-in-law from a competing Q&A site.

This emphasizes to me that the Slate article, itself, isn't from a peer-reviewed journal, and is a pretty ordinary reference. Can anyone do better?

  • Here's a link to the pdf (in French) that the city of Montreal sends out concerning recycling: ville.montreal.qc.ca/pls/portal/docs/page/enviro_fr/media/…. It says to please rinse for the benefit of the people who sort the recyclables.
    – Jonas
    Aug 7, 2011 at 20:00
  • @Oddthinking, Is "riper" the correct word here?
    – Pacerier
    Jun 10, 2015 at 6:24
  • @Pacerier: Idiomatically, ripe can also refer to smelling rotten. In any case, I am quoting a magazine here, so it wasn't my word choice.
    – Oddthinking
    Jun 10, 2015 at 13:26
  • @Oddthinking, Btw most articles are of course not "peer-reviewed journal". What do you mean by a "peer-reviewed journal" anyway?
    – Pacerier
    Jul 8, 2015 at 10:59
  • 1
    Do we really need a peer review article to confirm that food leftovers produce... less than pleasant effects when left in a warm place for a period of time?
    – user5341
    Jul 8, 2015 at 17:12

As an additional point to the existing excellent answers, if you have commingled recyclables, leaving food on the containers can lead to paper contamination.

Contamination in paper recycling is a serious issue, with negative effects ranging from the strictly financial, to the health and safety of industry workers. The rapid expansion of recycling programs has seen a commensurate rise in contamination of collected recyclables. The trend towards single-stream curbside recycling (where paper and other recyclables are commingled with refuse and sorted at a processing facility) has brought contamination to the forefront of debate.

Contamination in paper recycling can refer to soiling of paper with food, grease, chemicals, or other noxious compounds, or to the inclusion of inappropriate material for the intended paper grade.

Simple soiling is easy to understand; once you’ve used a newspaper to soak up transmission fluid, for example, it is no longer recyclable. Food can also be a source of contamination, which often comes as a surprise. The truth of the matter is that it is difficult to separate pizza grease (or other food contaminants) from paper fibers. This is a major issue in the hotly contested debate surrounding single-stream recycling, as food contamination seems inevitable.

Even if you're not throwing open cans of spaghetti sauce on your newspapers, if the bin is placed outside, there's a good chance that rain and dew can lead to the contents of the can pouring out over the paper (admittedly, leaving the paper out in the rain seems like it will degrade it anyhow, but that's probably another matter).

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