You mean you put beautifully risen bread into the oven and it flattens out?
What is your oven temperature? Are you preheating?
Is this yeast bread?
Linda C

During one rise or the other, or both rises, the dough is over-proofing. Because flour is no longer bromated, it doesn't have the extensibility it used to have to achieve "double", therefore just under double is now suggested for the amount of rise.

Avoid going by the timed amount suggested for the rise in the recipe - that's more often than not a BAD guess. Dough doesn't know how to tell time. It rises according to the strength of the yeast, ambient temperature, hydration and the amount of humidity in the air. It will rise slower when it's cold and faster when it's hot.

A simple way to judge your dough during the first rise is to skip the slant-sided bowl and use a straight-sided dough-rising bucket. You can use a recycled plastic container (ice cream bucket, canister, check restaurant supply stores for food storage containers with a tight-fitting lid, etc.), but an actual dough rising bucket has graduated markings on the side.

I generally use a 2-quart size, but I have a variety of larger sizes I use for different amounts of dough. I oil my hands for handling the dough and pat it into the dough-rising bucket. Snap the lid on tight. This is a perfect little environment for dough to rise. If I pat in 1-quart of dough, I'll know it's ready when it reaches just UNDER the 2-quart line. No more guessing.... If you use a recycled container with a tight-fitting lid, pat the dough in the bottom and measure that with a ruler. Double the measurement and mark the container (piece of masking tape - just make sure you know whether the top of the tape, or the bottom of the tape is the measurement).

Another common problem is using the incorrect pan for the amount of dough. If you place an amount in the pan that is too small and you allow it to rise more than double in order to fill the too large space, that will be over proofing. Scale (weigh on a kitchen scale) the dough to determine the correct size pan.

Approximate amounts of dough for the pan sizes and amounts of flour in a recipe:
Jumbo - 10x4-1/2 - 4-5 c. flour - 2+ pounds of dough
Quick Bread - 9x5 - 4 c. flour - 2 pounds of dough
Standard - 8-1/2x4-1/2 - 3 c. flour - 1.5 pounds of dough
Medium - 7-1/2x3-1/2 - 2.5 c. flour - 1 pound of dough
Small - 5-3/4x3-3/4 - 1.5 c. flour - 8 oz. of dough

Another possibility... With the proper amount of dough in the correct-sized pan, don't let the dough rise more than double before placing it in the oven. If you let the dough rise to the height you want the finished loaf, that's over-proofing the dough.

The log of dough is approximately 1/3 the size of the finished loaf. You allow that to double and that is equal to 2/3 of the size of the finished loaf. The ovenspring - the amount the dough continues to rise after it's in the oven - accounts for the last 1/3 of the rise.

Hope there's something in there that will help you out.

-Grainlady

Here is a link that might be useful: King Arthur Flour - dough rising bucket

Yep, overproofing just as Grainlady described. Many recipes say to let the dough rise (in the loaf pan) just until it reaches the lip of the pan (the top edge). The loaf will have some "oven spring" to rise it further as it bakes.

Teresa

This is a yeast bread that makes two loaves. I use the bread hook for kneading (as I must). After first rise, dough is divided equally in two metal bread pans for second rise. My oven temp has been checked.

Thank you all for your replies. I shall keep trying incorporating your remedies.

I agree, it's over proofed. And yes, I know it from experience. (sigh)

Don't let it rise quite as long/much during the last rise before baking and I'm sure that will make a big difference.

Annie

grainlady - thanks for the excellent post! I clipped it for reference.

So did I!