Bud Light made an enemy of the corn industry on Sunday by boasting in a Super Bowl ad that, unlike its fiercest competitors, it does not brew its beer with corn syrup. While corn lobbyists responded in anger, and competing brands fought back, some viewers were left to wonder: Does it matter if corn syrup is used during fermentation?“The bottom line is that the claims regarding corn syrup in brewing are more marketing than science,” said David Ludwig, a professor of nutrition at the Harvard T. H. Chan School of Public Health. Beer is made by fermenting sugar. During the fermentation process, yeast converts the sugar into alcohol.“Corn syrup is a form of sugar that’s been produced from a grain,” Dr. Ludwig said. “Whether that sugar is produced by first milling and then enzymatically treating the grain, or doing so from corn in a separate process, isn’t going to matter much to the final nutritional quality.”Bud Light’s ad came days after it became the first major beer to start listing its ingredients on its label. It lists just four — water, barley, rice and hops.In response to the ad, Kevin Ross, a vice president of the National Corn Growers Association, shared a video of himself pouring Bud Light down the drain.“Bud Light, if you’re not standing with corn farmers, we’re not standing with you,” he said.