Great question — answering as the UphillTech team:
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....
Full answer by Chris H: https://cooking.stackexchange.com/a/115639 (CC BY-SA 4.0).
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