Why are stems common in packaged raisins but uncommon in breakfast cereals? When I purchase raisins in the US, it is not uncommon that some of the raisins have bits of stem still attached to them.  However, when I purchase breakfast cereals with raisins included, I seem to never encounter stems.  Clearly there is a difference in how the raisins are processed.  But what is that difference?
What about the processing for breakfast cereals make stems so uncommon, and why is that same process not considered for raisins sold alone?  Is it the cost of some extra or different processing, or are perhaps all these raisins processed the same but then dividing into low- and high-confidence-no-stems pools, the latter used in breakfast cereals?
I've noticed a difference between raisin brands in the past. Given my habit of alternating weekly shops between the close/cheap supermarket and the well-stocked one I'd choose to buy them at the better shop, though I've had worse than even that cheaper shop.
From the better shop I find less than one stem in a generous handful of raisins (on my otherwise plain weekday Weetabix), but in the worst ones I've tried I've found a few every day.  This all indicates that there's a possibility for variation from some point in the production process.
Given that variation, so long the worst ones aren't added to breakfast cereals, and given the dilution by other ingredients, I'd expect to find very few.
In addition, there's no guarantee you'll find every single one.  On weetabix or porridge I've been known to spot a stem only to lose it when it sinks, but then not to find it when eating.  In something like granola with its range of textures and harder components I would be more likely to miss an occasional stem.