This is a variation on Seeded Multigrain Sourdough, one of my favorite breads for its reliability and versatility. It’s a great one to play around with, and playing around with your bread is highly encouraged!
For this one, I bumped the overall proportion of whole grain flour up to about 75% by using whole grain flours (equal parts spelt, wheat, and rye) instead of white flour in the final feeding of the starter, and increasing the amount of whole grain flour in the final dough as well. Because whole grain flours are extra thirsty, I also increased the water in the final dough.
Do not expect to get very good gluten development with this dough, because the gluten in spelt and rye is not very strong compared to wheat. Do expect, however, to get a chewy and flavorful bread that will keep well for several days!