Recipe from America’s Test Kitchen:
2 cups (8 oz) whole wheat flour
1 cup (4.25 oz.) unbleached all purpose flour
1 cup of wheat bran
1/4 cup wheat germ
2 teaspoons of sugar
1 1/2 teaspoons baking soda
1 1/2 teaspoons baking powder
1 teaspoon table salt
2 cups of buttermilk
375° middle rack, 40-45 minutes, rotate 1/2 way through. 185° internal temp. Cool for 1 hr.
I found, on initial mix, the dough was far, far, too dry. It kept crumbling apart and WOULD NOT hold together.
I kept adding splashes of buttermilk until I could get a loaf that would hang together.
Baking time had to go a little longer too, after 45 minutes it was only 145°. Maybe because of the added buttermilk. Running another 15 minutes brought it up to temp.
I’m not an expert on Soda Bread specifically, but am on bread. I looked up the source recipe, and it seems way off to me. The hydration with this much dry ingredient to buttermilk is way low, and is certainly going to make the bread crumble apart as you described.
Less than 50% hydration is more akin to pastry than bread, and I’m not even aware of any standard loaf recipes that go below 50% because it will just crumble apart.
The other thing is the addition of germ, and the way the recipe just says to mix everything together. Absolutely wrong. If you’re not blooming or otherwise hydrating germ separately, and just throwing it in with flower, it’s going to give a really weird and inconsistent texture with rough patches throughout the loaf. It’s also weird they don’t discuss kneading or resting for hydration because of the germ, but that’s a different topic.
At a minimum, you should try adding an egg to bind things together. I would also be weary of any online recipes that don’t measure by weight for baking. They’re almost certainly not coming out like the pictures they show.