In a medium bowl, stir together the soy flour, whole wheat flour, spelt flour, and salt. Add water, and mix by hand or in a stand mixer with the dough hook attachment. Use more water as needed to form a stiff but pliable dough. Mix or knead by hand for about 10 minutes. Cover, and let the dough rest for 30 minutes, or if you do not have a pasta machine, rest for at least an hour.
Divide dough into four pieces for easier rolling. Run dough through a pasta machine if you have one, or use a rolling pin to roll out very thin, but not transparent on a floured surface.
If you are making noodles, allow the pasta sheet to dry for a few minutes. Dust with flour, and roll into a loose tube. Slice the tube into 1/4 inch slices for linguine, or to desired size.
To cook: Bring a large pot of lightly salted water to a boil. Add pasta, and cook until al dente, 1 to 5 minutes depending on thickness. Cooked pasta will float to the top of the water.
