Online news portal Slate expects to garner nearly half of its 2019 revenue not from stories on its website, but via podcasts that it pushes. Slate President Charlie Kammerer says the company has built a “healthy eight-figure business” from podcasts, which a year ago accounted for less than a third of its revenue.

“We got into podcasting 18 years ago, so we’ve been doing it a very long time. But many of those years we literally made no money. The reason we got into podcasting was because this curious, affluent audience that we had, liked to listen to audio,” Kammerer said. “It became a real advantage for us because we learned how to do it well. We had studios. We made a lot of mistakes. But we ended up knowing how to do audio.”

Kammerer’s comments at the recent Digiday Publishing Summit are featured in the latest Digiday Podcast. In the episode he adds that audio has become the biggest driver of subscription sales for Slate, which offers exclusive content to the 25 podcasts it produces for subscribers.

Slate’s focus is mostly on news, politics, technology and culture, but it is history that has proved to be most successful category for podcast downloads. The biggest show Slate has released to date is “Slow Burn,” which examined Watergate in its first season and the Clinton impeachment in its second. Both shows have had about a million downloads to date, according to Kammerer. Among topical shows, he said “Political Gabfest” leads the pack, with about 180,000 downloads per week. “The numbers are growing big time,” he said. “If you look at the total, we’ll deliver just under 200 million downloads this year with our family of podcasts and next year about 250 million.”

That has attracted advertisers, including more brand marketers. Three years ago, three-quarters of Slate’s ad dollars came from direct response clients. This year DR will represent about 20%. “The brand guys are coming in a really aggressive way,” Kammerer stressed. The company has also embraced branded content, with Slate producing 12 shows for clients this year, including Ford, Century 21, Progressive and Prudential.

This year has seen hundreds of millions of dollars invested in podcasting from existing media companies like Spotify and Entercom and from venture capital firms. It has some questioning whether podcasting has become a “bubble” business. “Audiences are doubling year over year so people are coming and listening and that would tell you there’s a reason to invest,” Kammerer offered. “The argument for yes is a couple of these companies have been bought for a lot of money and we’ll see whether this can be turned into a long-term growth strategy that’s going to work.”

Rather than raising money, he thinks the toughest thing to do in podcasting today is creating “something that is big” with more than 600,000 podcasts now available. “If you don’t have a kind of podcast ecosystem to promote it in—we’re lucky we do, because we have a lot of shows—it’s hard to build an audience.”