is opening the oven door mid-bake bad for the bread Inside?

Sure I've been tempted to open the oven door mid-bake before but I wanted to explore if it is that bad for the bread and whether it is ever a good idea. Here's the short answer first:

It's a pressure thing...

As an oven heats, the pressure of the air inside increases. The hotter, the higher the pressure.

If you open the oven door, the pressure created from the heat is released. It’s what's going on when I open the door whilst standing in front of it. The moisture and hot air fly out like I’m being attack!!!

If the pressure gets released before the crust forms the bread will collapse like a cake in the same scenario.

So yes, it’s not a good idea to open the door!! But that’s not quite the end of the story about opening the oven….

….There are two periods when opening the door improves the breads quality, I’ll explain...

The first 5 minutes 

During the first 5 to 10  minutes of the bread going into the oven, ovenspring happens. The dough rises rapidly to its final size from a burst of gas in the bread. It’s  created by the remaining active levain meeting with the heat from the oven. 

The addition of steam in the oven at the start of baking helps the oven spring and the crust texture.

If you want to open the door during the first 3 minutes of baking to add steam to aid the oven spring then it’ll be ok to do so. The crust structure has not formed yet, neither has the pressure built. At this point it is still ok to open the door.

As promised, here’s the other time when it’s good to open the oven door.

The releasing the damper trick

The other time that’s ok to open the door is after the crust has set for the last ten minutes of baking. 

In a professional bakers oven there is a damper lever which opens a hole in the rear of the oven. This lets the steam out and reduces the air pressure. You only need to open it a little though, but it can work wonders on the quality of the bread. 

Opening the door at this time allows the steam to release and helps create a golden, crisp crust. So it can be a good thing to do if you want to bake professional quality bread at home. 

So yes, do not oven the oven door but do if you do it at the right time…. Awful grammar, I know!! Keep baking, speak soon.