What to Know When Choosing and Eating Manila Clams:
Manila clams are the sweetest and probably the smallest hard-shell clams you will find in the market, making them the favorite of many professional chefs.
Accidental arrivals from Japan in the 1920s, Manila clams are easily spotted by their pretty shells and small size. They sport deep, wide bars of color over a finely ridged shell that makes them distinctive. And while Manila clams can live for 7-10 years and grow to eight inches across, most are sold at 3-4 years old and less than 3 inches across.
Manila clams live in the wild next to the Pacific Littleneck, which is not to be confused with the Eastern Littleneck clam. Incidentally, do not mix the different types of clams in the same dish unless you cook them separately -- Manila clams need only about 3-5 minutes to steam open, while Pacific Littlenecks require 10-12 minutes.
Manila clams are widely -- and sustainably -- farmed in the Pacific Northwest, mostly in Washington State and British Columbia. Unlike some kinds of fish farming, clam farming poses little threat to the environment because the tasty bivalves are hatched in pens and then live their lives in the wild.
From a cooking standpoint, most Manila clams are steamed. You can certainly eat them on the halfshell, but few people do for no real reason: They taste every bit as sweet as the Eastern quahogs we eat on the halfshell, although Manila clams will be less salty.
Manilas are classically used in pasta and soups.
Pair Manilas with some kind of cured pork, such as bacon, pancetta, chorizo or something else that's porky and salty. And if you want to mix them with another seafood, try crabs, Pacific perch or flounder. Why? All three eat Manila clams in the wild, and they share a connection on the plate because of this.
And the bottom line? Manila clams won't break the bank. They are typically sold by the pound and 1 dozen is a healthy main-course portion for one person. Personally? I can eat several dozen, and it is always better to have too many than too little, so as a general rule I buy a dozen for each person, then an extra dozen for good measure.
One more note: Any clams that did not open their shells after steaming should be tossed. It's likely they died before you got them and can possibly make you sick if you eat them.