That crackling sound you hear is the bread “singing”.
It’s why you should never cut into a piping hot loaf of bread fresh from the oven, tempting as that may be. Let it rest and sing for awhile as it finishes the process of baking all by itself.
Here’s what Jim Lahey has to say about singing, in his book My Bread, which is where I get my bread recipes and technique –
Just after you take a loaf out of the oven, something strange often happens: it begins to make wierd noises, a rapid-fire crackling sound, one pop after another. This “singing” as some bakers call it, is especially loud and obvious in the professional bakery, where dozens of loaves may be pulled out of an oven at the same time and placed together in a basket. They become kind of a snapping chorus. The singing lasts for several minutes – the temperature of the room will determine how long – as the bread cools.
This singing is evidence of the last phase of cooking, which takes place out of the oven- and is why you should always given a loaf time to cool before slicing it. The exterior of the loaf is very dry at the moment it’s removed, but the interior is still wet. During cooling, the two elements of the bread start to even out somewhat, although the crust will remain brittle and the crumb soft. The crust is shrinking and cracking. Steam escapes through the cracks, which is the racket you hear, as it forces its way through, while the crumb solidifies. At this moment, the bread seems alive.
I know its a romantic idea, but it’s how you get to feel when you fall in love with a simple, but beautifully baked rustic loaf.
So wait till the song is over before you cut into that loaf of bread. It’s well worth the wait.