San Francisco may be a nexus of wine worship, but you can't reach any of those wineries in Napa, Sonoma or Mendocino county on a city bus — much less walk to one from downtown inside of 45 minutes.

You can, however, get to the Anchor Brewing Co. that easily. For the price of bus fare or some extra mileage on your shoes, you can while away a couple of hours on a weekday afternoon touring the premises and sampling the products. Think of this reservations-required tour as a field trip for grownups, a chance to see, hear and smell how an everyday product gets made in historic surroundings.

As a bonus, the trek to Anchor's slightly scruffy Potrero Hill neighborhood, sliced apart from downtown by freeway ramps and railroad tracks, shows a different side of San Francisco. Here, cheap burrito places are not hard to find, white-tablecloth restaurants are, and many of the warehouses lining these streets are, so far, just warehouses.

Anchor's trim, 1937-vintage building fits right in. I felt like a trespasser as I opened the front door, walked into an empty lobby that smelled faintly of gingerbread, and headed up a flight of stairs to tell the receptionist, "I'm here for the tour."

Anchor is an old-school place, lacking a bar or restaurant to sponge up visitors' cash. With the tasting room closed for a TV interview of brewmaster Fritz Maytag, there wasn't even one room for everybody to meet in. So all 25 or so of us congregrated by a table on the shop floor, next to windows offering a distracting view of downtown.

Had Anchor signed a lease instead of buying in 1977, that vista would surely have ensured its conversion into granite-countertop lofts years ago.

Our guide, Kate, cheerfully outlined how things would work — "We'll take the walking tour, and then we'll serve you some beer" — and then launched into a recap of the brewery's history. It dates to 1896 and almost went under a few times before Maytag (a descendant of the appliance magnate) bought control of it in 1965.

Anchor remains a midget among microbreweries: about 50 employees and 85,000 barrels a year. So it was easy to follow her explanation of the basics of brewing as we walked past gleaming copper mash tuns and brew kettles set on a tile floor — just like the illustrations on beer labels. A wooden oar, the paddle turned black and flecked with green stains, leaned against one wall. That, we were told, is used by the staff to stir hops into the wort (unfermented beer, which smelled like black bread and tasted first sweet, then astringent).

Some of those hops filled plastic yellow barrels along a hallway. I leaned over the pile of dull green flowers in one, breathed deep and got a wonderfully bracing whiff of pine cones and citrus.

Right after came a glassed-in room hosting huge metal trays, maybe 3 to 4 feet deep and filled with a gnarled beige mass. They set Anchor apart from most other breweries; its franchise brew, Anchor Steam, ferments in those trays instead of deeper tanks.

This technique began in the 19th century as a crude work-around to allow brewers to whip up a lager beer without refrigeration; the shallow trays allowed the wort to be cooled by chilly Bay Area breezes. Back then, they'd be left on the roof of a brewery — where, our guide mentioned, "anything flying by, from airborne yeast to pigeons, could get in the beer." (Somehow that didn't threaten Anchor's survival, but the onslaught of Bud, Miller, Busch and Coors in the '50s and '60s did.)

After a stop in the hop-storage room, a prison-like space lined with 200-pound bags of hops, we headed downstairs to the bottling line.

That room boomed with the sound of hundreds of beer bottles clanking and rattling their way through hissing machinery. They blurred as they spun around corners, while excess foam drifted up like snow on the floor: Homer Simpson's idea of heaven.

Our last stop covered the step between fermenting and bottling, a basement room filled with conditioning tanks. In these, lagers are krausened, ales bunged (brewing has a deliciously esoteric vocabulary) and beer generally allowed to age a bit before being funneled into bottles by the raucous machinery around the corner.

The beer geeks among us fired off a round of exceedingly knowledgeable questions that I barely understood, and then we returned upstairs for the tasting.

The menu featured Anchor Steam and six others: Summer Beer, a refreshing wheat brew; Small Beer, a bitter oddity made with barleywine leftovers; Liberty Ale, a hop-intense pale ale; the oil-black Porter, with notes of chocolate and coffee underneath; Special Ale, the different-each-year Christmas brew, a spiced pumpkin pie of a beer; and the pleasant Barleywine.

Even in small samples, it all added up. Eventually, somebody had to ask our hosts: Do you get some kind of employee discount?

Yes, the answer went, and a free case of beer a week — that's our employee allowance.

I took another sip, looked out the window for a moment, and sighed inwardly.