Unfortunately, while this is correct, it is nowhere near strong enough.

Just because you know the initial hypothesis that drove someone to throw the onions in, doesn't mean you know what the onions are actually doing. The onions are interacting with all the other ingredients. Onions are more complicated than you think.

Before you remove the onions you must understand what they are actually doing in your recipe, not merely what you think they are doing... or you must be prepared to find out. Because even very tiny systems are generally too complicated for you to fully understand, you usually have to settle for science: You must have good enough test coverage to detect any breakage as soon as possible after the onions go out, so that you may frantically throw the onions back in and then go back to the drawing board.

And the longer the onions have been in the recipe, the longer the recipe has evolved in the presence of onions. Take the onions out and all the other changes that have happened since the onions went in might have to be tweaked. Oh, the subtle things you could find.

Here is what can happen: You'll take out the onions, and then five years later your customers will complain that your company's red paint has started peeling, ten years ahead of the fifteen-year warranty period. Oh, no. You call an all-hands meeting of your QA team. They spend months doing expensive research, while your product engineers fly from city to city trying to pacify the increasingly irate customers. Eventually the scientists find that the paint can be fixed by mixing in some kind of protein or other. But why did the paint used to work? Oops, the onions had protein in them! Sure enough, if you throw in some special Essence Of Onion Protein compound the problem goes away. Great. Now all you have to do is issue a field recall of about six years worth of your product.

You will bring this story to your CEO and the shareholders, and they will ask why you didn't just pay for some onions? Or, if removing the onions was critically important, why you didn't run a small set of onion-free test batches on a parallel process line and then put those batches through lots of tests, both in the lab and in the field, before making the change?

I've worked as a semiconductor engineer, specifically in charge of diagnosing problems that arose in the field, so believe me when I tell you that I've seen "simple", "well understood" little tweaks in a semiconductor processing recipe cost companies millions of dollars and one hell of a lot of stress. I've also lost six months of my grad student career to one specific bad step in a recipe. Once you get a working recipe you do not change a thing without a specific plan to thoroughly measure and document the effect of that change. Find someone from Intel and ask them how this works: I've heard that you can't so much as touch a knob in Intel's fabs without a signed change order.