I've often wondered how I can be sure I've eaten a KeZayith of flour when I eat something small but complete - like one cookie - and struggle with the decision of whether or not to eat more in order to be sure I need a Berachah, or whether to rely on the Safeik and not make one.
It just occurred to me that (at least in the U.S.) food labels can be a guide to help in this process. If it were possible to break down the caloric value of a KeZayith, it might then be possible to figure out, from the labeling, how much flour is in the food item.
For example, there are 3.87 calories in a gram of white sugar, and according to many sources available online, the standard sugar content for commercially prepared cookies is 24.73 grams per 100 grams. A similar calculation should be available for oil/margarine, etc., this despite the fact that all products are proprietary and recipes vary, because the fat content and sugar content (as well as fiber, protein, and others) are displayed on the side panel of the packaging.
It should be possible, then, to determine by process of elimination the maximum amount of flour contained in a serving based on these calculations. Then it's a simple game of division to determine, from the information on the panel, how many cookies (or other food products) are in a serving, and divide by that number.
Personal note: I'm a liberal arts guy. Even if I sat down with a paper and pencil and started doing all the calculations myself with the amazing math skills I acquired in high school (since I avoided math in college), I wouldn't assume I had factored all the variables or even come up with the correct calculations. Can anyone shed some light? There might even be a resource from the USDA or somewhere that already has this information broken down into digestible (no pun intended) nuggets.