While I've recently revived a sourdough starter and have been keeping it going on my counter, I've also thought that it should be possible to have a ready to use product similar to instant yeast. Perhaps I'm spoiled by the homebrew shop where I can buy dozens of different yeast packets and even some lactobacillus for making sour beers. So when I saw packages of Seitenbacher sourdough on Amazon I bought a box and have now tried out making some bread using it directly, rather than trying to build a culture with it. This is what the company intends, but so far it's not been smooth sailing.
The first go round I mixed up a batch of wheat dough at somewhere around 65% hydration and tossed in the contents of the 2.65 oz package. I mixed up the dough and let it hang out overnight for 12 hours. I then shaped and proofed it for something like 8 hours at 85-90 F. What I wound up with after baking at around 450 F for 40 minutes or so was a flat disc with a very gummy center. So- not enough gas, but I'm not sure if it was over/underproofed, or if the beasties in the packet objected to being required to work on wheat instead of rye, or if should have baked it longer & lower to try and bake the crumb before the crust burns. So many variables!
On the off chance that it was a shaping issue I put the other half of the dough in the fridge for 24 hrs or so before taking in out and warming it an oven at around 85-90 degrees. I did some stretch and folds and then shaped and did the final rise in a colander lined with a floured towel, again at around 85-90 degrees. The total time between coming out of the fridge and baking was about 8 hours. This time the shape was dandy, but the crust still gummy(and I could swear it sound hollow when thumped.)
So, deciding that when all else fails, read the recipe, I used the recipe for Farmers Bread from the sourdough package, which calls for some rye flour and instant yeast as well as the sourdough. The result was fine, but not up to par with bread made with my continuously maintained starter.
As folks have used this product to build a sourdough starter it should be possible to use it to make good bread without adding instant yeast, but I haven't figured it out yet. The package instructions do say to warm the packet to 100 F before using, but not how long it should be kept warm, maybe that's where I'll look next. For now I'm having better success with my existing starter.