FOREST OF CHOICES: Shimeji, left, king trumpets, center, hen of the woods, back right, are making their way to major markets. (Mark Boster / Los Angeles Times)

To this day, even though transportation is not the same sort of issue and horse manure is no longer widely used for growing, Pennsylvania still accounts for more than half of all the cultivated mushrooms grown in the United States. California ranks second with less than 20%.

Hokto's plant in San Marcos is as far removed from Swayne's operation as a rocket ship is from a horse and buggy.

The plant is located at the end of a valley that looks like it has seen better days. You approach the building on a dusty road. Then you make a turn and there it is: metallic white and gleaming in the sun.

It's huge -- 250,000 square feet spread across two floors. And it's hugely expensive. Though the company won't talk about specifics, officials acknowledge that by the time everything is up and running it will have cost at least $50 million.

The operation is terrifically ambitious, even for Hokto, a company that has 25 mushroom-growing facilities in Japan. There, each operation grows only one kind of mushroom, either maitake, shimeji or king trumpet. Here, they're growing all three.

In its rough outlines, the process is similar for all of the mushrooms, but each type requires its own set of specific circumstances including temperature and humidity and will have its own zone in the new building.

From the mixing of the substrate to harvesting and packaging, the process is entirely automated and the mushrooms are never touched by human hands. They are grown in plastic bottles, following a technique developed by Hokto in Japan (they switched from glass after the 1964 Niigata earthquake).

The bottles are first filled with the substrate, which is then inoculated with mushroom culture. Over a period of weeks this creates a root system called mycelium in the bottle and eventually, given the right conditions, that root system begins to produce mushrooms. Depending on the variety, this can take from 1 1/2 to two months for maitake and king trumpet, to more than three months for shimeji.

Reuse, recycle

THE mushrooms will all be certified organic and the plant in San Marcos is designed to be almost astonishingly green. The spent substrate, already mostly recycled material, but now enriched by the mycelium, will be recycled yet again for animal feed and other agricultural uses and the bottles will be reused on the next crop. The only waste product will be distilled water from the sterilization process.

Furthermore, the plant is so energy efficient that it has qualified for a $500,000 rebate from San Diego Gas and Electric, the largest in the utility's history.

Right now, the mushroom-growing process is just beginning. The first run of bottles is being inoculated and the first mushrooms probably won't be ready to sell until early next year. In the meantime, the company is selling mushrooms from its Japanese plants under the Hokto and Golden Gourmet labels.

The first year's production goal is ambitious: 4 million pounds. To do that, Anderson says, they're going to have to break out of their old markets and into the mainstream.

That could be a challenge in a country where mushroom eating has always been a little outside the mainstream (Anderson describes the U.S. as "mycophobic"). But, he says, headway is being made. "It used to be I'd hear, 'Was it raised in [manure]? Will I see colors if I eat it? Will I die because they're poisonous?'

"Those are the hurdles we have had to overcome. It's been an uphill battle, but we're gaining traction."

One thing that should work strongly in these specialty mushrooms' favor is their rich flavor. Not long ago, portobellos went from being a growers' mistake (they're actually just over-mature creminis) to being one of the hottest items in the produce section because of their meaty taste.

These mushrooms have the same potential. Though they won't begin appearing in great numbers until early next year, they are in Asian markets such as Mitsuwa, 99 Ranch and Marukai right now. And since fall seems like the perfect season for mushroom eating, you might as well get started.

Maximizing flavors

AS WITH any mushroom, high heat when cooking is the key to getting the best taste. Mushrooms are very high in moisture and it takes that kind of temperature to concentrate the juices and begin the browning process.

This is particularly true of the shimeji and maitake mushrooms, which really need to be cooked well to get the best taste. Though their flavors are different in nuance, they can be used interchangeably.

The place they really differ is in appearance. So if you're going to be cooking something where the mushrooms need to look nice -- such as the topping for the halibut baked in parchment -- the shimeji are a better choice.

On the other hand, the maitake mushrooms, though cosmetically disadvantaged, have a really rich, woodsy flavor. Use them for dishes where looks aren't so important -- pureed in a soup for example, or as a filling for lasagna or crepes.

King trumpets are the only ones of this group that are good raw, and they are very good indeed, with a meaty texture and mild, slightly briny flavor. Cooking them doesn't seem to improve the flavor much, but they do pick up a nice delicate crust if you sear them well.

Serve these as you would young, firm porcini: slice them thin (lengthwise so you get the full effect of their size). Strew them across a bed of lightly dressed arugula greens. Shave Parmigiano-Reggiano in long, thin strips over the top and finish with a scattering of toasted pine nuts.

Then take just a moment to revel in the thought that fairly soon, once-exotic mushrooms such as these may be as close as your neighborhood supermarket.