So often when I take the little barcode sticker off the piece of fruit when I'm washing it, I discover a blemish under the sticker. Is that because the sticker was placed so as to cover up the blemish, or because the act of putting on the sticker tends to result in some local damage to the fruit?
A few years ago I had the rare chance to take a look behind the scenes of the largest manufacturer of fruit sorting, labeling and packaging equipment in the Pacific Northwest and it was impressive to see how much effort and planning goes into designing everything in a way that damage to fruit is avoided at all costs. We talked about how the business evolved and what the biggest challenges are.
And yes, the stickers are a crucial part. Developing a glue that is food-safe, will stick well and come off without damaging the fruit is a challenge and different manufacturers have solved it more or less well. If you observe carefully, you will notice that the stickers will behave differently.
There are two main ways how stickers can lead to damage:
- Too much local pressure when applying the stickers and
- A glue that is too sticky and tears the fruit when the sticker is pulled off.
The former will result in a soft spot or other blemish, the latter is visibly fresh. Soft-skinned fruit like peaches are much more prone to damage and a real challenge compared to e.g. apples. The damage is not unavoidable, a lot depends on the settings of the equipment and a good operating personnel.
But I can assure you that no fruit packaging plant will “cover up” blemishes with a sticker - simply because they label way too many pieces per hour. Blemished fruit will be sorted out before packaging, damaged fruit in packs will typically mean the whole package is rejected by wholesalers - because they won’t travel and store well.
Knowing all this, one of my pet peeves is supermarket workers that think refilling displays is best done by upending boxes of apples, but that’s not part of your question.
I've often wondered the same thing. Here's a video of stickers being applied to fruit: https://www.youtube.com/watch?v=62nJzuKjUBc
Since it's done mechanically, there's no way to intentionally cover up the bad spots (without spending more money than it's worth). So in other words, the bad spots under the stickers are a coincidence... unless the stickers are moved later on by, say, an employee at the store.
Assuming that the stickers weren't moved, here are a couple of other possible reasons that stickers seem to cover up bad spots so often:
- some sort of "confirmation bias" (we remember those particular cases because they support our suspicion)
- the fruit with visible bad spots weren't chosen by the customer
As a student, I used to work at one of the biggest vegetable and fruit processing/trading companies in the world. (They would import/export fruits and vegetables all over the world, and would also sell bags of pre-cut vegetables for instant use).
One of the most boring jobs was putting the stickers on the fruits. Because this was all still done manually. This was done with some kind of "sticker-gun", that gave you a sticker if you pulled the trigger, after which you had to press the tip of the gun on the fruit.
I can imagine that this pressure would be enough to cause a small bruise, that would become visible several days later.
Also: They had some kind of "deal" with a local daycenter for the mentally handicapped. I think it was 3 times a week, the ones that were able to do some basic labour (mostly down-syndrome) came to do some of the basic tasks. One of those tasks was putting the stickers on the fruits.
I can imagine that, even though they were very hard working and responsible, they would have slightly less control of how much pressure they had to put on the fruit and sticker-gun, causing the bruise to be slightly bigger.
Edit: forgot to answer part of the question: in no way was it done on purpose to hide existing bruises. This task was already extremely boring and time consuming, so that no one would take the time to find a bruise to put the sticker on. You would just do "tack tack tack tack", and place it anywhere you could, as fast as possible.
I'll offer up an alternative explanation to the two that you mention in your question. Like Stephie explains, stickers are generally applied by automated machinery in a process designed to minimize damage. The packaging process also includes steps to weed out damaged fruit before shipping. If a machine happens to place a sticker so that it covers up existing damage, then the inspection process would be significantly less likely to notice that damage and flag the fruit. It's not malicious sticker placement to fool the buyer, it's coincidental sticker placement that allows an existing blemish to slip past quality control.
I don't have any direct experience with fruit-processing machinery, but I've seen this sort of thing happen on other types of manufacturing/processing equipment. There's a lot of probability involved with the coincidental cover-up so the odds of this happening to a particular piece of fruit are quite low, but multiply that times the volume processed and you get a reasonable chance of this occurring a couple of times a day.