Pure fresh semolina pasta with and without eggs

There are two pasta manufacturing techniques. First, pasta can be cut to shape using a blade or roller, and second, it can be extruded at high pressure through a bronze or teflon die. The first is what most people know of as fresh pasta, and is made using common flour and eggs. The second is made using semolina flour and water. If you are using a standard Atlas or Imperia roller, or cutting with a knife, use flour and eggs. It is the traditional technique and the semolina will not make a good pasta. If you have access to industrial pasta extrusion equipment, use semolina.

Semolina is typically made from a different species of wheat, durum wheat, which has a very high gluten content, so it does not require eggs to bind it together. The egg white has very high protein content, which compensates for the lower protein in common flour. In McGee's, "On Food and Cooking" he explains how the extrusion process aids the formation of a firm pasta:

The movement, pressure, and heat of extrusion change the structure of the dough by shearing the protein network apart, mixing it more intimately with starch granulas that have been partially gelated by the heat and pressure, and allowing broken protein bonds to re-form and stabilize the new network.

In "Essentials of Classic Italian Cooking", Marcella Hazan says:

"[semolina] is the only suitable flour for industrially produced pasta, but I do not prefer it for home use. To begin with, it's consistency is often grainy, even when it is sold as pasta flour, and grainy semolina is frustrating to work with. Even when it is milled to the fine, silky texture you need, you must use a machine to roll it out; to try to do so with a rolling pin is to face a nearly hopeless struggle. My advice is to leave semolina flour to factories and to commercial pasta makes: At home use unbleached all-purpose flour.

Eggs are definitely not necessary to make fresh pasta. Pasta is in fact traditionally made just with durum wheat, salt and water in a number of Italian regions. Just to cite a few examples:

• Trofie and pansoti in Liguria;
• Orecchiette, cavatelli and strascicati in Puglia;
• Fileja in Calabria;
• Scialatielli in Campania;
• and many more...

It is very possible to do this at home by hand, even using an Imperia roller. The tricky bit is to get the proportions or flour vs water right. If you get any traditional Italian cooking book, you will most likely find no information regarding the exact quantity other than "add water, quanto basta (i.e. enough water). My suggestion would be to put the flour and salt toghether and then add the water little by little until you get the right, elastic texture. Note that at the beginning, the dough will be dry and crumbly; make sure that you knead it well before adding more water, otherwise you will end up with a very soft dough.