I'm making an irish red and going to try a yeast starter for the first time. Does it matter what kind of DME I use for it?
Not really, as long as you're decanting the spent starter wort before pitching the yeast in your beer wort.
If you chill (cold crash) the starter the yeast will settle into a nice cake on the bottom and the wort (actually now a not too good tasting beer) on top. Just pour off the wort/beer and then pitch your new yeast cake into your fermenter.
It's pretty neutral in small amounts, so if I don't have time to crash and decant, flavor/color isn't affected. I also once heard that the extra protein in wheat DME vs. Pils or Gold helps nourish yeast, and I figure that sounds plausible enough. (I have no scientific back-up for this)
extra light is my preferred DME for starters because it is well, extra light. decant the slurry first as described though, and try not to pitch anything but yeast. it's not particularly hard. Cheers.
Do yeast use protein directly? I don't think so, but I could be wrong. They do use free amino nitrogen (amino acids/peptides) which are building blocks for protein.
I use Pilsen Extra Light DME. It has a very light taste, so if I do end up throwing the entire starter into the wort, it doesn't affect the taste much. I always try to decant when I can, but sometimes (not very often) I don't have the time to chill the starter and so end up throwing the entire starter into the wort.
