If that winds you up, I suggest you read the
weights & measures legislation. If you thought that the weight marked on the pack is the minimum allowed you're in for a disappointment, your bag of coffee's allowed to be as little as 209g as long as the batch average meets 227g. Of course, you as the consumer have no way of knowing or proving what the rest of the batch weighed. It's donkey's years since I first noticed food was coming in under weight, and that that's permitted, but it got no interest at all when I made a noise about it on MSE. The 340g jars of Tesco peanut butter I buy are 320g: the minimum limit they can get away with. Years ago I noticed their tuna was also underweight, but I haven't checked it lately.
Average system
"You can pack your products to an average measurement that is on the label. You must check your packages to make sure a random sample is packed to meet all these rules - known as the ‘three packers’ rules’:
- the contents of the packages must not be less, on average, than the weight on the label
- only a small number can fall below a certain margin of error, known as the ‘tolerable negative error’ (TNE)
- no package can be underweight by more than twice the TNE"
Note the absence of a definition of
"a small number".
Having worked in the food industry for most my life, on checkweighers for 20 years, its a couple edged sword with lots of factors...and ultimately, I long since learned as soon as you introduce humans into the equation, you may as well not bother.
(For the wider audience) A checkweigher is effectively a CCP (critical control point..it MUST be right)...but lots of technology comes before it to ensure the product weight is correct BEFORE it gets there, dosing, weighing etc etc that's usually designed to achieve the most efficient legal weight. To fail before the CCP is a complete waste of time and money...and the customer will.pay.
The LAST thing a manufacturer wants is excess rejects, in our grape packing factory, they would often UP the giveaway to avoid repacking product, its costly and time consuming.
There's a final reality check though, one I failed to solve in those 20 years...
Sadly, lots of fthe food industry is staffed by agency staff...they often don't understand, or occasionally don't care...and will circumvent entire systems in the.name of 'getting the job done'...which occasionally meant I'd witness staff taking underweight out the reject bin...and.placing them on the final product conveyor (

Im glad I've retired, having standards just doesn't seem to be as important anymore, I can't tell you the times I raised this in meetings, with staff, with QC...a week later...you're seeing the same thing again
But...a.small amount of.'acceptable' underweights will smooth the production process...therefore keep cost down to a degree.