Suppose you’ve just had an amazing new beer from a craft brewer you know little about. You want to know more about their history, where they’re located, what else they make, etc.

So, you go to the brewery’s website and the first thing you see is a message like this:

“You must be 21 years old to enter this site. Please enter your birth date below.”

What? Why? I’ve been drinking beer for years and just want to read about your brewery? Even if I were a kid, I’m not buying beer from your website. Why do I have to prove my age, like I’m at a supermarket check-out line with a six-pack of Bud?

I visit a lot of brewery websites and face this scenario on a near daily basis. And I wondered why jumping through this hoop, however trivial, was necessary.

I’d always assumed it was some kind of federal law. But turns out, it’s not.

“I don’t believe there is a TTB (Alcohol and Tobacco Tax and Trade Bureau) regulation,” said Paul Gatza of the Brewers Association, a craft beer trade organization. “Each brewer that does have an age gateway would choose to do it or not.”

Sure enough, not everyone has a verification — but about 90 percent (my unscientific guestimate) of alcohol websites choose to have it.

So, if it’s not law, then why do it? There’s got to be a compelling reason. A former car salesman told me that the chief goal in selling a car — in fact, selling anything — is to remove every possible barrier between yourself and the customer. There should be no hurdles that the customer has to cross in order to buy something.

Age verification seemed like a hurdle customers had to cross. So I asked a couple of brewers why they did it.

“We feel that as responsible brewers we must educate and encourage responsible drinking,” said Jessica Paar of Boston Beer Co., makers of Samuel Adams. “When advertising and marketing our products, we adhere to standards established by the Beer Institute and by the Brewers Association, our two industry trade organizations that set voluntary standards.”

Liz Melby, of Harpoon Brewery, said pretty much said the same thing.

“We use age verification on our website because we are complying with our trade association,” she said.

OK, so no specific law, but a matter of code with trade associations. But why would it come from them? The simple answer is that they’re trying to calm the anti-alcohol mobs in state legislatures and Congress.

In promoting the industry, one of the primary missions of  trade groups is to advocate for their constituencies in state legislatures and Congress. That means convincing often stubborn and panicky politicians that brewers are not a menace to society.

Going back to that car salesman analogy, trade associations want to remove any hurdles between themselves and the customer (i.e. lawmakers) on pieces of legislation, such as this one in Wisconsin, that could harm the industry.

Marketing appears to be a significant factor in these debates, according to the Beer Institute’s Beer Advertising Facts document.

“As funny and entertaining as (alcohol ads) often are, however, some find controversy in alcohol beverage advertising, focusing to a great extent on beer ads,” it says. “The critics move quickly from complaints to calling for unique restrictions and even outright bans.”

And so, to avoid these problems, the Institute makes these recommendations in its Advertising and Marketing Code.

“Brewers should employ the perspective of the reasonable adult consumer of legal drinking age in advertising and marketing their products…”

“Brewers are committed to a policy and practice of responsible advertising and marketing. As a part of this philosophy, beer advertising and marketing materials are intended for adult consumers of legal drinking age.”

“Beer advertising and marketing materials should not depict Santa Claus.”

The Santa Claus thing might seem a bit silly, but if there’s a chance of grade-schoolers being talked into chugging a barleywine, then brewers want no part of it. Nor should they. Alcohol companies have to make a good-faith attempt at making sure their audience is adults, especially if they don’t want to add to the pile of regulatory compliance issues that might be more difficult to meet.

But it’s not just trade groups that are policing this. Gatza said that age-appropriate marketing is an important part of complying with Federal Trade Commission guidelines.

“One thing that the FTC looks at is making sure that alcohol beverage marketing audiences are at least 70 % of legal drinking age,” he said. “FTC would consider a website as a marketing tool, so that may be one reason.”

But lets not be cynics, here. It’s not all about getting regulators off their backs, right?

“Another could be that it is a matter of responsibility as a good community citizen,” he added.

Which is pretty much what Paar of Boston Beer Co. said.

“We think that age-gating is the responsible thing to do,” she said, “and we take all reasonable steps to ensure that visitors to our websites are 21 or older.”