There's not much information there to go on, but it seems you might be underestimating the effects of making changes in your bread dough or the way you handle it after mixing.

If you want specific changes in the way your bread behaves, you usually need to start being more fussy about things like:

• weighing all ingredients to get a consistent starting point
• using the same flour, or recognizing that diff. flour gives diff. results
• getting a consistent final temp in your dough after mixing
• mixing for the same dough consistency (moist feeling) every time
• mixing for the same gluten development every time
• using the same qty of yeast and salt every time
• fermenting the same amount of time at the same temp, or making shorter or longer adjustments to accomodate changes in temp
• covering the loaves during proofing to avoid the development of a hard skin
• proofing to the same degree of loaf tension or inflation every time
• Baking at the same temp that worked for you before

I realize that's a lot to consider, but, unless you're willing to see wide variation in results, predictable baking can require very specific observations and procedures.

What seems like an insignificant change in yeast could actually cause a big difference in the gas pressure in the loaf.  The amount of yeast and salt used in bread dough is small, but that's precisely because you don't need much to cause great changes in the dough.

The change in mixing procedure (featuring the use of a higher speed) will develop the gluten in your dough more than before.  That makes the dough stronger.  Perhaps you need to proof a bit longer to allow the dough to expand more and accomodate the greater volume that usually results from greater gluten development.  A blowout at the side of a pan loaf sometimes means a longer proof was necessary.

I'm not suggesting that the problem must be the yeast or the change in mixing.  But if you try to think back to every ingredient and every minute detail in procedure that you followed to get the loaves you liked before, you may be able to find the change (or changes) that are now frustrating you.

Hope it goes better next time for you.  Reading a very good, accessible book like Hamelman's Bread might help in the long run.

--Dan DiMuzio

Also, are you putting the loaves too close together in the oven?  This causes blow-outs too...