I've been thinking of making compliant sour dough bread for me and my DH for a long time but haven't done it. Recently I'm tinkering with the idea again. 100% rye is a bennie for him whereas teff is a superfood for me, so I thought, "Why not?"

My question is, what about the sour dough culture? What food category is it under and does it carry any value or change the value of the bread/grain itself, much like the way yogurt or cheese change the value of milk?

You can make your own sourdough starter with rye flour, water, and time. I've done it in the past (the distant past, when I used to add wheat flour to the sourdough starter before baking.) It basically involves making a sticky dough and letting it sit out at room temperature for a few days-but I know there were some more details about how to do it "right" that I can't think of right now, but an internet search should turn up plenty on the subject.

The bread I buy is 100% sourdough rye, so I know it's possible to make a sourdough starter that is entirely without wheat; just have no idea on how to do so...That's where Google comes in handy.

Christina has a complete thread on her expertise making SB and starters using compliant flours......a search will most definitively take you there

I make spelt sourdough bread and sell starters.  You can buy dry or frozen starters.....kinda pricy so taking time to collect your own is worth it as described by Ruthiegirl.   I have collected my own yeasties also, but use 1 part water to 1 part flour, cover and leave at room temp for a week or more.  Perhaps a local search will yeild someone close who sells some " live ones".
A very useful trick is to work in 1 tsp. baking soda when you knead the bread to  sweeten up the sour taste some.  I sure can tell when I forget the soda.    

So what's the deal with San Francisco? I've heard it said that the "air quality" here makes particularly good, sour sourdough -- Do you have an opinion on that?

http://www.sourdo.com/

Just found this, scrolling around for info re: San Francisco's distinct sourdough (Type I).
This site is for buying sourdough yeast... A whole variety is offered...
You can choose the region of the world you want to get a culture from!
Note: San Francisco is at the TOP.   But all sorts of unusual locations are listed. Looks like fun, if bread-baking is your thing.

It appears that, while they don't specifically say it, all the cultures are wheat-based.

There is a rye based sourdough starter recipe at:

http://www.food.com/recipe/rye-sourdough-starter-and-bread-382968

Hey, thanks! Sounds easy enough!

MsRubyLu - nice link on Rye starter and bread -
Can you tell me what it is in oz and cups?

100 grams
100 ml
800 grams
300 grams
450 ml

Purlgurl: http://www.exploratorium.edu/cooking/convert/measurements.html

Drea thank you so much - talk about teach a girl to fish instead of just answering the question.
I marked it as a favorite.  

It's a favorite for me, too, which is why I was able to find it so quickly!

Thanks Drea,  I only have the conversions in a book