Put the Bin on a Scale Before You Choose a Dose

Six in the morning, back dock, and the 120-litre bin reads 41.2 kg gross. The tare plate says 12 kg, so there is 29.2 kg of waste in a bin the crew has been dosing as if it held 18. That single number explains three weeks of wet loads, and it took eleven seconds on a platform scale to find.

Kitchens almost always estimate waste by volume. Volume is not weight. Two bins of the same size can differ by a factor of two, because a bin of soup, sauce and stock is close to the density of water while a bin of bread, packaging and trim is closer to a third of it.

The density range you are working with

Mixed commercial food waste typically runs 0.35 to 0.55 kg per litre. A full 120-litre bin holds between 42 and 66 kg when level, and more when the crew stacks it above the rim and closes the lid on the bulge. A 240-litre bin can pass 100 kg without anyone thinking it is heavy.

Now compare a dose table written in grams per bin. If the table assumed 40 kg and your bin holds 65, you are running at 60 percent of the intended dose. The gel forms, looks acceptable on the surface, and releases liquid the moment the bin is tipped — which is where the complaints come from.

Dose per kilo, with a volume sanity check

The workable rule is 12 to 18 g of polymer per kilo of waste, moving up the range for wet loads and down for dry ones. That converts an 18 kg salad bin to about 250 g and a 65 kg stew-heavy bin to 900 g or more. The gap between those two numbers is why a single scoop for all bins never holds.

Weighing every bin every day is unrealistic. Weigh once a week, per bin, at the same point in the shift, and write the figure on a strip of tape on the lid. Within a fortnight you will see which bins are consistently heavier than their label, and those are the ones to re-dose.

The failure that started this

The site above had a 240-litre bin in the staff canteen, dose card saying 400 g, actual load 96 kg on a Friday. The gel set on the top 10 cm and formed a crust that held the rest of the liquid like a lid. When the compactor ram came down, the crust broke and roughly 20 litres of brown liquid went into the sump in one go.

Nobody had done anything careless. The card was simply written for a different bin, and nobody had checked whether the kitchen’s actual loads matched it.

Nominal litres are not usable litres

A 240-litre bin does not hold 240 litres of food waste. The lid hinge, the internal ribs and the taper at the base eat into it, and a load that reaches the rim without spilling is closer to 190 litres. Stack a bulging bag on top and the true figure drops again.

This matters because a dose table expressed per bin is really a dose table expressed per nominal litre, and the conversion to kilos depends on what the kitchen actually throws away. A fish prep bin at 0.6 kg per litre and a pastry bin at 0.3 kg per litre are not the same job, even in identical bins on the same card.

What to put on the scale and how often

• Weigh the empty bin once and record the tare on a label — castors and lids vary by 3 to 5 kg between models.
• Weigh the full bin at close, before dosing, once a week for a month.
• Log date, bin number, gross weight, and what was in it in five words.
• Recheck after any menu change, banquet season, or new collection frequency.

Four weeks of that log gives you a dose table that matches your kitchen rather than a supplier’s average. The dosing guidance is a starting point; the scale is what makes it true. Start with your heaviest bin, not your busiest one.