Lots of people get hung up on ppm, which is vexing because it really is a meaningless number. Like percentages, which ppm is a form of, most people have trouble understanding what they really mean.
Here is an example from the percent world. You make $20 per hour working for me. Times are really tough, so I insist that you take a 50% wage cut just to keep your job. 50% of $20 is $10. Your new wage is $10 per hour. Oh, wait, we just got a huge contract from a new customer. I can give you a 50% increase in your wages. That reverses the cut, right? Wrong. 50% of $10 is $5 and your new wage is $15 per hour.
Tests can detect 20 ppm or 5 ppm or some other detection threshold. A product tested for 20 ppm may, in fact, contain 19 ppm or 0 ppm, or any amount in between.
Let us assume that we have two baked products. One is tested for 5 ppm and the other for 20 ppm. Let us also assume that each is right at the detection limit, say 4.9 ppm and 19.9 ppm--that is not a valid assumption, but let's run with it for the moment.
Let's eat a 10 gram serving of the 20 ppm tested product. That's 196 micrograms of gluten.
Now, let's eat a 40 gram serving of the 5 ppm tested product. Holy cow! We still ate 196 micrograms of gluten.
What matters in terms of the gluten-free diet is the total amount of gluten ingested, not whether it came from dilute or concentrated sources. And I cannot repeat enough times, tested to X ppm does not mean contains X ppm. The content is less and is often far, far less than the test threshold.
I hope that helps. If not, let me know, but I didn't want to bury you in mathematics. It was my major...
You didn't bury me. You have just set me straight. Since we are dealing with arbitrary numbers and voluntary labeling and testing, there is no way to truly know what is being ingested.
The safest bet (for me) is the whole foods approach, at least until I figure things out. I just wish that would happen soon.
Peter, your information has been invaluable. I thought this website was a great resource, but now I see that the moderators are a big part of that. Thanks again.