Some people can pick between Coke and Pepsi in blind taste tests. Only a few can explain what separates bourbon from whiskey. And it often takes a parent to know which twin is which.

Yet nobody—absolutely nobody—can tell the difference between sugar that comes from GMO crops and sugar that doesn’t.

You can look at the sugar with your eyes. You can taste it with your mouth. You can even have expert scientists study it at the molecular level using ultra-powerful gas-spectrometer analysis.

And still, nobody can tell the difference.

So why would anybody want the U.S. Department of Agriculture to try?

A few anti-biotech activists are demanding that USDA make the futile attempt, as part of a new federal GMO disclosure law. Over the next few months, regulators will propose a series of specific rules—and one of the first they’ll have to consider involves refined products.

“USDA’s biggest task in writing the rule may be deciding whether highly refined products like beet sugar, soybean oil, and high fructose corn syrup would need to be labeled because they are derived from genetically modified plants,” wrote Agri-Pulse, a weekly newsletter.

This may be a big task, but it has a simple answer: Putting GMO labels on highly refined products is pointless.

In July, President Obama signed the Safe and Accurate Food Labeling Act, passed a few weeks earlier by bipartisan majorities in Congress. It wiped out the threat of states creating a confusing patchwork of expensive and contradictory regulations for labeling food with GMO ingredients. In return, the law mandated national standards—and now it’s up to USDA officials to propose what this will mean in practice.

Logic would suggest that a food should carry a GMO label only when some element of it can be traced back to a GMO source.

With highly refined products, however, this is impossible—and sugar offers a great example of why.

I grow sugar beets on about 7,000 acres in Idaho, and also belong to a cooperative that supplies about 10 percent of America’s sugar.

We prefer to grow GMO beets because they make economic and environmental sense, helping farmers like me to fight weeds and conserve natural resources as we produce more food on less land than ever before.

When we harvest our beets, we pull up the conical roots that contain a high concentration of sucrose. Next we slice them into strips that look like French fries. Then we boil these pieces, freeing the sucrose from the fiber. Finally, we evaporate the water and crystalize the sucrose, producing the pure white sugar that you buy in grocery stores.

By the time this intense process of refinement converts our crops into granules of sugar, it has erased any indication that the original plant was the product of biotechnology.

Even if it didn’t, it wouldn’t much matter: GMO foods are safe and healthy to eat, according to everybody who has examined the matter, from the American Medical Association to the World Health Organization.

Yet nothing distinguishes the sugar of GMO beets from the sugar of organic beets. They are totally the same, all the way down to the molecular level.

So why would we want to label sugar as GMO or non-GMO? It doesn’t make any sense.

It would also be a lie.

We label products to inform consumers about their contents. Slapping a GMO label on a package of sugar, however, would reveal nothing about the makeup of the sugar. It would simply identify a mode of agricultural production.

That’s not a label for food. That’s a label for a farming practice, which is not the same thing. Pretending otherwise is either an act of ignorance or an act of deception, and it’s outside the scope of the Safe and Accurate Food Labeling Act, too.

As regulators develop the particular rules that will govern the details of the new federal law, they may encounter a number of thorny questions with no obvious answers. The labeling of highly refined products, however, is not one of them.

This is a clear case of a rule that doesn’t need to be written.