Smart Sieve would be a good invention
Some of the biotech researchers are working to develop 'microsniffers', organic materials mounted in electronic platforms that can detect all sorts of chemicals.
A neat use of this would be a Smart Sieve or a Soup Magnet. You could pass liquid or soupy food through the Smart Sieve, and it would remove all the gluten, or all the bits of onion, or all the sodium....
Wouldn't help with religious restrictions. If you're Muslim or Jewish or Vegan or whatever, you have to know for sure that the forbidden item was never in the food at all.
But it would help hugely with organic restrictions.
What brought this to mind: My old belly can't handle onions any more. I always eat the same Campbell's chunky soup for supper, and most of the time it doesn't contain any onions. (The ingredient list doesn't show onions either.) But different factories appear to use different recipes, and when I eat a can that contains lots of onion bits, I become a highly efficient methane generator.
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Later: Come to think of it, I could probably do the filtering task with a plain old non-biotech strainer or colander. Pour the can through the strainer into the pan, and sort through the solids to pick out the onion slivers. Wouldn't be perfect, but would be easier than spotting them within the dark liquid.
Better, I could make my own soup with full control of the ingredients. I used to do that in hippie days, and it was both satisfying and cheap.
But I'll leave the dumb idea here in case it somehow inspires a not-so-dumb idea in a better mind than mine.
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Much later: Finally implemented the make-own-soup recommendation in March 2012.
Definitely worth the effort; not just a calmer belly but better health in general! (But not cheaper; costs about the same.)