Help, fan oven problems
So i have a major problem just when i thought i had everything right (so annoying and am pulling my hair out over it.)!!!! I have changed to a fan oven recently as my old oven was rubbish and couldn' hold temperature, anyway the fan oven is my only choice at the moment. I made a great starter about a month ago and is wickedly sour, doubles real easily and is fed twice a day everyday. So i add a couple of spoonfulls to about the same amount of bread flour (a good brand that does the job Allisons extra strong between 12% to 13.5%) and add a splash of water which makes a thick batter and leave for 12 hours overnight on the kitchen top which is not too cold or warm. In the morning the batter has about doubled and bubbly with good gluten structure. Next i add about the same weight of flour and another splash of water and a teaspoon of salt to form a dough which is tacky but not sticky. I stretch fold and knead for 20 mins, autolayse and stretch and fold once more for 10 mins before leaving the dough about six hours to rise and double ( sometimes i give a quick knead after three hours to even out the big air bubbles). Ok finally in the afternoon i form a boule and let it proof on a thick gauge baking iron baking sheet for about two hours finally baking at 450 degrees farenheit with oven of until it drops to 400, usually takes about six mins to get down to 400f and i have to turn the fan oven back on, rest of bake is roughly around 400f and entire bake is 35 mins. Oven spring lasts approx ten mins and definatly over after fifteen mins.
I use to think the rising times and proofing times were way too long but i get good oven spring and the crumb is airy and final boule is easily four times the original dough size from start to finish.
The problem comes in about the thirteenth to fourtenth min of baking at the end of the oven spring, the loaf has puffed up, grown in size and expanded, filled the slashes i put in it and looks beautiful, then on cue the right side blows out like a massive eruption raising that side up in the air and making the left side dip down, imagine lifting a manhole cover on oneside and thats the path the top of the loaf takes. Ok they look ugly but make great sandwiches and the crumb is delicious but this simply wont do.
I've tried lowering and raising the temp of baking but nothing makes any difference, tried steaming and placing a baking sheet in front of the fan so as not to cover it but stop it blowing on the bread but still the same problem. I cannot block the fan completly as it is not safe to do so and won't consider it. So realising it is always the right side that blows out and up i inspected the oven and, although it may make no difference, saw that the fan spins from left to right (clockwise as i look at it) and was thinking that this could be the reason the right half of the oven is hotter and blowing the right half of the loaf out.
More evidence to go on is that after 15 mins of baking when the loaf has done its little erupting act i have decided on the last two bakes that i didn't want another deformed loaf and terminated the bake. Took half baked loaf out of the oven and cut in half so that i had a good cross section from the left, slightyl risen side, to the right, erupted mega risen side. One thing stood out and that was a ball of dough in the centre of the right side that was still gooey and not turned to bubbly bread crumb as the rest of the loaf had. At 15 mins the crust had started to form and was crunchy to cut through.
My shaping is good, seams are sealed and the skin is tight, add a bit of steam at start as well but its a fan oven so dont bother steaming that much, prefer to just wet the dough before slashing. I thought that i might be underproofing but ive tried proofing till the loaf fall flat and still they erupt.
Anyone who can help would be greatly apreciated, especially Minioven and chuck as you have the answer to a lot of technical questions people have asked and have given me invaluable information before. I make bread almost everyday and have a lot of experience but this is really making it not fun. I don't weigh anything as i like to do it by eye and kind of think i have a good feel for it. Is this a common fan oven problem or am i serioulsy going backwards, PLEASE HELP!