Q. I bought several pounds of "Chesapeake mussels" from a local fish merchant. They were large and had ribs on their shells. I cooked them in oil, basil, tomatoes and onions until they opened. They were very salty. Why?

A. There are two types of mussels found in the Chesapeake. Near the mouth of the bay--between Cape Charles and Cape Henry--are found Mytilus edulis, the blue or New England mussels, common to all oceans and shores. Farther up the bay, near the Bay Bridge and Annapolis, where the water is less saline, there are several species of ridged mussels, one of which is Brachidontes recurvus.

Also called marsh or horse mussels, the ridged mussels live in mud and have a musty flavor. Blue mussels, on the other hand, live attached to pilings or rocks and are continually washed with clear water.

All mussels are isosmotic, that is, their flesh contains the same concentration of dissolved salts as the surrounding water. Thus, the Chesapeake mussels which you bought were actually less salty than the more expensive and tasty blue mussels.

Why, then, were they so salty? Probably because in your effort to get the shells open, you cooked them too long. Thick shells conduct heat poorly. When mussels are heated slowly, they often stay closed. Or perhaps you reduced the cooking liquid too far, or didn't add enough water or wine to begin with. Salt is not soluble in oil; the sauce may have been 90 percent oil, 10 percent brine.

Q: How can I make my own liverwurst?

A: In Germany, where the liver sausage called leberwurst is king, there are a number of varieties: braunschweiger, zwiebelwurst (braunschweiger with bits of browned onions), truffelwurst (flavored with truffles), hildesheimer strichleberwurst (made with calves' liver rather than pork liver), kasseler liverwurst (flavored with garlic and herbs) and leberkase (baked rather than smoked in terrine rather than a pork or beef casing).

Most people prefer liverwurst as smooth as possible. This is difficult to achieve even with a food processor. Sausage makers use grinders which extract liver proteins which, along with fat, form a stable, smooth emulsion. It's sort of a meat mayonnaise.

Here is a home recipe which takes into account the inefficiencies of home equipment by adding egg protein and bread crumbs to serve as binder and moistening agents. LIVERWURST (Makes a 2-pound sausage) 1/4 cup bourbon 1/2 cup crumbled, stale white bread (after removing crust) 1 pound pork liver, trimmed and ground 1 pound boneless pork shoulder, ground 1/8 teaspoon each of ground black pepper, ground cloves, nutmeg and ginger Salt and pepper to taste 2 or 3 eggs (depending on size)

Combine bourbon and crumbs in mixing bowl, blender jar or food processor. Add meat, spices and whip or pure'e, adding the eggs one at a time. The mixture should have the consistency of a thin mayonnaise.

Bake this mixture in a well-greased or bacon-lined loaf pan set in another pan of water. Bake at 350 degrees until the center registers 160 degrees, about 2 hours.

This wurst can be eaten cold or hot. If eaten hot, it is traditionally served with fried onions and apples.

Q. The following recipe is for a large and very moist black devil's food cake. Every time I bake it, though, it sinks. When it is rising, it looks as if it will overflow. What's wrong? 1 cup shortening 1 1/2 cups sugar 4 eggs 1 cup cocoa 3 cups flour 1/2 teaspoon baking powder 2 teaspoons soda 1 1/2 teaspoons salt 2 cups water 1 1/2 teaspoons vanilla extract

Cream shortening and sugar. Add eggs 1 at a time and beat. Mix dry ingredients together. Mix water and vanilla together. Then blend in the dry and wet ingredients alternately by thirds to the egg mixture. Bake in greased and floured pans at 350 degrees for 45 to 50 minutes.

A. Whenever a cake rises high, then sinks, the problem can be solved in one of three ways: decrease the sugar, cut the leavening or increase the flour.

For the sake of comparison, I converted yours and seven other chocolate cake recipes to ratios. Yours comes out a little less sweet than the others, which is quite all right. However, it is too low in flour and too high in leavening. You might try this: add another half cup of flour and delete the baking powder. Do not tamper with the soda, as it gives the cake its deep color. If the cake still rises too high, add more flour. It it doesn't rise enough, add less.

Chocolate cake should be made with all-purpose, not cake flour. All-purpose makes a chewier cake and also turns stale less quickly. If you prefer the crumbliness of the cake flour, use half all-purpose, half cake flour. Never use all cake flour unless you're making an egg-leavened cake like the German and Austrian tortes and the French genoises.

Q. In your column of July 6, 1981, you said that sunflower seeds turn green in applesauce cakes and banana breads because a substance in the seeds, chlorogenic acid, reacts with iron, copper or aluminum. Why not just use glass baking pans?

A. There is enough of these metals in fruits and vegetables to cause the greening of sunflower seeds. And baking powder supplies plenty of aluminum in the form of the salt, sodium aluminum sulfate. If those metals were picked up only from the pan, then only the seeds at the surface of each loaf would turn green.