Well it depends if you are talking PROPER sourdough or that stuff they sell in the shops (which is normal bread with a little sourdough starter mixed in for flavour).
Sourdoughs tend to be heavier (due to the process of making it - I have no worries with my Sourdough sitting under my other shopping.) and don't have packet yeast (packet yeast is problematic for some people). It DOES however contain yeast - wild yeast that is grown and cultivated and kept alive in a water/flour mixture (sourdough starter or culture).
You can get heaps of different sourdoughs (wheat, spelt, rye, multigrain, wholemeal...blah blah). Just thought I'd drop that in cause some people think sourdough is a specific type of bread rather than a way of making bread which is what it is.
I recommend Summer Kitchen Sourdough (which is the place I get mine and where I worked). They do sell up in Launnie, not sure where you live, but I know that Grand Central Station gets them (delivered Tues and Fri I think?). If that's not near your way, let me know what areas of Launnie you get near to and I will check the closest for you!
Apart from Summer Kitchen, most good German bakeries would do a good sourdough and many places are getting it now as it becomes more popular (just watch for the inclusion of packet yeast which is CHEATING!!!!!!!)
*steps off soapbox*
Does that help? Sourdough tends to be a bit more expensive (because it uses more flour, and it is more time intensive, and in the case of Summer Kitchen, also organic), but IMHO, soooooo worth it
35kg lost. (November 2005 - October 2006)
15kg gained again (as at October 2010).
Back to the drawing board - Let's do this thing!
"You can't change the winds, but you can change the sails"
"Reach out and take control of what lands in your lap"