How to prevent baking turtles?

Matthew, I agree with chem, although I'd add that during the initial baking stage a good healthy dough expands, especially if it contains a significant amount of wheat flour. However, the main reason for cutting dough pieces correctly prior to entering the oven is to control the expansion - allow it to occur within the cuts - which if done correctly produces beauty in the appearance of the bread.

One of the reasons for the type of uncontrolled expansion seen in your photos could be a lack of final proof. Perhaps more proof time and or cutting a little more deeply prior to entering the oven. The general rule I use is that the more [b]under[/b] proof the dough piece is the [u]deeper[/u] the cut, and the more [b]over[/b] proof the [u]shallower[/u] the cut.

...some nice tips from the others...

...also take care to give your loaves a sufficient final proof...

underproofed loaves have a tendency to blow-out in spectacular fashion -such as your "turtles"

take care

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My question is what caused the loaves to burst out the side like that?
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Uneven molding and excess molding pressure,,,,

Compared to batard where is more evenness the pressure is more evenly distributed so there is less likelihood of bursting along the sides

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By excess molding pressure do you mean stretching the dough too tight when moulding the boule before placing in the banneton?
Would deeper slashes or a different pattern of slashes help? Or do I need to concentrate on improving my shaping technique?
Slashing may help but its not the right solution.
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You have to improve your shaping technique?..there is a difference in pressure applied on the boule by each person depending upon the molding skill and the less experienced he or she is in dough molding there is the tendency to ? over do ? the step.
Tightening a dough skin by allowing your palms to met underneath the dough while turning the dough piece around is the easiest and simplest way of creating the boule, but it has the tendency to exceed it in some points in particular the dough skin resulting on hair line fissures( and weak points) that may or may not be noticed or not visible right at the end of the boule molding process.

Dough extensibility and resilience varies from dough recipe to another.
Another thing that influences this is dough hydration and even flour quality and blends.
100%White wheat flour doughs are robust to this and hence is less likely to burst in sides , but mixed grist and whole grain dough are less and tend to get taut and less extensible and prone to the formation of what you call bread turtles if you are not careful with your boule moulding.

There are many techniques in molding a boule and they have the same aim... is to mold it uniformly but not too taut that it will create minor hairline fissures that will manifest to burst during the later stages in proofing or during the baking process( oven spring).

The tightening the skin is one way, but how about the inner portion of the dough there are still ?unevenness? where it can initiate bursting in odd places including sides.

The nature of intermediate proof (before the dough is finally molded)can also influence the fault. If the dough is given less intermediate proof it will still be a bit taut and also if the dough is allowed to rest more, the dough becomes bucky or overmatured.

Bakers may divide a huge bulk of dough necessitating them spend quite a lot of time molding that some dough pieces already had attained an extended intermediate proof to the point of forming a bucky dough ;or the dough seems a bit tight to mold and fissures can easily forms in the weakest area where that during later proofing or during baking can manifest as burst sides.

In either way its better to feel each dough and if over rested there is a need to degas the dough slightly before creating a skin around it so that large pockets will not be the source of focused pressure that during dough expansion the overextended part will burst at the weakest point resulting in the defect you had experienced.

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There seem to be many slightly different techniques for moulding a boule. I tend to tuck the dough under into a relatively loose round and then let it rest on the bench for about 20min and then dust the flour off the bottom and, using both hands push back and forth across the bench with a bit of a curling motion so it rotates as well until the skin is quite taut and the dough sits up quite high (I'm trying to make it look like a nice round ball without tearing the skin). Then leave it on the bench for a few seconds before placing in the banneton seam up. I do not pinch the bottom seam together. Any suggestions on improvements to this technique?
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Well your method looks satisfactory but I am not sure about the inner characteristics of your dough piece.

My method is a bit difficult to learn ?.for beginners.

I mold the dough with both of my hands, ( regarding the dough size)
I hold the dough , one in each hand doing the moulding simultaneously like rounding small pieces of dough done in circular fashion.
I may cup the small piece of dough and round it easily or spread my fingers around a bigger dough piece while doing the same thing.

The rested dough balls are placed on top of the bench each hand pressing the dough gently to press large gas bubbles out while turning around( circular fashion). While doing that the edges of the dough are folded into the center until it forms forming a hemisphere( a half ball) which is then turn upside down the seam facing the table surface. Then grasping the dough, still one piece in each hand I cup my palm around the contour of the hemisphere allowing my four fingers to spread around the hemispherical dough shape my thumb pressing the sides down, the heel of each palm pushing the dough downward and forward while the thumb will control the sides and I twist my wrist while moving my palms in spiral motion to ward the center (just like with what I do when rounding small pieces of dough.) When I feel that the dough is firm, the skin tight I stop. I have to feel the dough that its not over extended but has the right tautness, shape and symmetry
There is a very thin line that separates and undermolded and overmolded dough and only with practice you can feel the precise end point of each molding process.

Further on molding bigger dough pieces; the dough during the boule molding process tends to met each other in the center as you twist and turn them to form a ball .

Matthew ...

I quite like your 'turtles'!

Carol.

i like the look of them care to share recipe?
turtles are my thing