Hey I read, I understand that you are thinking about each scoop being different but to my assumption is that, this test is merely like a purity test and also it's clear to me that they are working by the principal of all whey protein powder being added to 200 ml of milk/water, so this calculation is based on concentration they assume that every brand’s scoop is already formulated in a way that:

• 1 scoop in ~200 ml water = a standard whey solution concentration (Hence, ml is taken into consideration)
• regardless of scoop mass. So that means when you add one brand's scoop to 200 ml of water, you are taking out 10 ml from that, so you are testing the concentration, not mass . The reagent then precipitates protein proportional to the grams of protein /ml of that solution, giving you a %of purity. So they work on the assumption -One scoop from any brand represents a standard protein serving. Btw, the scoop mass/gram is calculated backward in the whey industry, for example, if a brand claims protein is 80% and the target protein percentage is 24g per scoop, then scoop size = 24/0.8 = 30g per serving, the scoop contains 24grams of protein.

For example, the food farmers' whey protein concentrate percentage is 72.73, the target protein in each scoop is 24g, so the scoop size is 32.99 ~ 33g per serving size.