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Composting Fat and Oil Residues from the Kitchen - By Angus Stewart
We are sometimes asked whether it is OK to put fats and oils into home composting systems, whether they be compost bins or worm farms. The answer is yes, but it needs to be done in a way that overcomes the fact that they are not water soluble. Most of us know instinctively that it is not a great idea to flush these substances down the sink. Images of 'fatbergs' clogging up sewerage systems appear from time to time in the media, conjuring up rather unpleasant images (and realities for the poor folk who have to deal with such situations). For those who have domestic septic systems there is often a grease trap to stop the passage of these difficult to break down substances entering the main septic tank. Cleaning out a grease trap is not a job for the faint hearted! Composting them is a much better and totally do-able option, so let’s explore how to make it happen.
As mentioned above, the difficulty of disposing of residues of fats and oils is that they do not dissolve in water, meaning that they form fatty blobs or oily slicks that are difficult to process in waste disposal systems such as septics and sewerage systems. A very common scenario is when residues of fats and oils are left on dishes that need to be washed. Dishwashing detergents are used in hot water as a chemical substance that enables fats and oils to become suspended in water, making them easier to remove from dishes, pots and cutlery. The problem is that they then will congeal in the waste water after it goes down the sink, causing problems downstream.
We find that a great way to stop these residues clogging our waste water systems is by wiping the residues off with paper towelling and then mixing that oily/fatty paper towelling with your kitchen scraps before adding this nutrient rich resource into your compost bin/worm farm. Warming up the dirty dishes will make it easier to dislodge congealed fats, particularly in cold weather.
Distributing fats and oils with the cellulose of the paper towelling dilutes these substances so that the earthworms and microbes in your composting system are not confronted with big blobs of fat and/or oil that are much harder to break down. Also, the high nutrient and energy content of the fats and oils makes a significant contribution to the nutrient content of the finished compost produced from such inputs.
We find this solution particularly effective in our worm farming products such as the above ground Worm Café, Can-O-Worms, Tumbleweed Cube or the in-ground Tumbleweed Worm Buffet as the earthworms have no problem chewing through the paper towelling fat/oil mix.
We have been using this method of composting fats and oils for decades and find it a convenient and effective way of dealing with this messy problem. Keeping fats and oils out of our sewerage and waste to landfill systems is a no brainer on so many levels. It also allows us to create rich organic fertilisers that are perfect for the garden as well as being free.
Happy composting!