I’ve been doing some quick reading on what causes bread to tear or ‘blow out’ while cooking.
Unsurprisingly most people deal with regular bread, with wheat flour and kneading. The relevant discussions talk about how the oven spring causes the the bread to expand too fast for the ‘skin’ of the bread, which will then tear at its weakest point.
One way to deal with this is to tear the skin yourself, which is why kneaded loaves are often scored before cooking. Given the rather liquid state of the rye dough before cooking, I’m not sure this will work, but it might be worth a try.
Another way is to lessen the oven spring, and given my rye sourdough goes in at max oven temp for 15mins, the obvious solution might appear to be to reduce that time/temp to lessen the oven spring. But of course we want that oven spring, especially with the dense rye dough, to give a lighter crumb.
Finally one suggestion I’ve found is too increase the moisture of the skin so it can expand more. You can do this by spraying the load with water just before going in the oven. This sounds like my best bet, so I’m going to try that on the weekend.