thoughts on adding commercial yeast

Hello, 

after years of making reasonable basic sourdough loaves I thought it was time I experimented a bit.

I followed a recipe for flaxseed bread from Wild Yeast whcih turned out very tasty indeed (if a little dense - I think I overproofed).

Anyway, the recipe threw up a couple of questions I would love to get the answer to from the clever people on here. Firstly, why does the recipe call for such a tiny amount of starter? It says 17g. For a batch as big as it makes I would be looking at more like 400g! Secondly, why the need for commercial yeast? I'm not against it per se, I just wonder why not simply use more starter and a longer proofing time. I do suspect that with such a low gluten bread (there's a lot of rye and flax in the recipe) it needs a bit of help rising, but I just don't know.

Any help on these questions is gratefully received. The recipe is below (and delicious if you want to give it a go)

Flaxseed Soaker Ingredients:

• 91 g whole flax seeds
• 273 g water

Rye Sourdough Ingredients:

• 364 g whole rye flour
• 290 g water
• 17 g rye starter

Final Dough Ingredients:

• 182 g whole rye flour
• 364 g high gluten flour (such as King Arthur’s Sir Lancelot)
• 119 g water
• 4.5 g (1.5 t.) instant yeast
• 17 g (generous tablespoon) salt
• All of the rye sourdough
• All of the flaxseed soaker

Method:

1. To make the rye sourdough, mix the starter and water, then add the rye flour and mix well. Cover and ferment for 16 hours at room temperature.
2. Make the soaker at the same time you build the sourdough. Combine the flaxseeds and water, cover, and let rest for 16 hours.
3. Combine the fermented sourdough, soaker, and the rest of the final dough ingredients in the bowl of a mixer with dough hook. Mix in low speed to incorporate all the ingredients, about 3 minutes. Adjust the water as needed to achieve a medium consistency dough.
4. Continue mixing in medium speed until the dough starts to hold together, which will indicate the gluten is developing. If you can get a windowpane, it will be a very crude one. This might take about 3 minutes, but will depend on your mixer. The dough will be very sticky.
5. Transfer the dough to a lightly oiled container. Cover and ferment for 45 minutes at 80F. (I roughly achieved this temperature by placing it into a large plastic bag with a cup of hot water.)
6. Turn the dough into a lightly floured counter and divide it into two pieces. (My pieces were 730 grams for the batard and 930 for the round.) Preshape into balls and let rest, covered, for 10 minutes.
7. Shape the dough into tight rounds or batards and place them, seam-side-up, into well-floured brotforms or linen-lined baskets.
8. Proof, covered, for about one hour at 80F. The loaves are proofed when the surface shows the faintest hint of “cracking.”
9. Meanwhile, preheat the oven, with baking stone, to 460F. You will also need steam during the initial phase of baking, so prepare for this now.
10. Just before baking, slash the loaves as you like, at a 90-degree angle to the surface of the loaf.
11. Bake at 460F with steam for 15 minutes, then without steam at 440F for another 35–45 minutes, until the crust is a deep brown. Then turn off the oven and leave the loaves in for another 10 minutes, with the door ajar, to let the loaves dry.
12. Cool on a wire rack, then cover with linen for several hours before cutting.