This was my first attempt working with flax seeds. I got a bag of brown whole flax seeds from the grocery store, soaked them at 300% hydration for 12 hrs. Separately, I made a 3lb / 1362g dough at 68% hydration using 90% AP flour, 10% einkorn flour, and a touch of honey (5%). 20% of the flour was a liquid levain at 125% hydration, 50% of the flour was a cold flour soaker at 80% hydration. For the flax seed soaker, I wasn't sure in advance how many seeds I'd want in the dough, so I just soaked a bunch of seeds, more than I'd need.
For some reason I had thought I could treat the seeds as a hydration-neutral component. After soaking, the seeds had absorbed most of the water, but what remained was a gelatinious, kind of slimy, soupy mixture. I tried straining them but not much drained. So, I went ahead and began spooning them into the final dough and incorporating by hand, until I had a lot of seeds in the dough to my satisfaction. This also significantly increased the hydration of the dough. I spent about 30 minutes attempting to develop the dough by hand, slap + folds, kneading, etc., to no avail. More of it was glued onto my hands than in a cohesive dough on the workboard. :-)
So I ended up adding 4 heaping spoonfuls of additional AP flour. I hated to do it, but I had to. :-). I let the dough rest for 30 mins, then resumed stretch / slap / folding for another 20 mins. That helped, but the dough was still very sticky and felt more like an 80% hydration dough. After a long bulk ferment and more S&Fs, the dough did come together more, but relaxed very quickly. I probably should have baked in a pan, but instead I tried it in the brotform and free-standing in the oven. Upon the end of final-ferment and removing from the brotform, it blobbed out horizontally quite a bit. To my surprise, it did get some upward spring in the oven, but next time I definitely need to factor in additional hydration being added by the flax seed soaker.
So that's all the bad parts. The good part is -- tastes great! :) I couldn't remember what flax seeds tasted like beforehand, but once I tried it -- "ahhhh... I remember now.". They do taste very nice, and I see why people put them in bread, quite complementary.
Here's some pics.