Could bread be baked in a mailbox when the temperature is 100°F (37°C)?

Question

Texan journalist John-Carlos Estrada recently reported on Twitter

How hot is in Texas?? This woman BAKED BREAD IN HER MAILBOX!! Roberta Wright, who lives in a suburb of Houston, posted these photos on Facebook to show just how hot it is! She truly baked the bread in her mailbox!! It took 45 minutes! 📸: Roberta Wright Twitter (archived)

The recent weather in Houston, Texas has been daytime highs around 100°F (37°C).

Is it plausible that a mailbox would reach temperatures sufficient to bake bread?

Answer 1

No

Bread is typically baked at between 350 and 475F (180 and 246C) I did a bit more research and found it's possible do do it at lower temperatures. It did take 45 minutes and the bread doesn't have to be perfect so we'll use 300F (150C) as a minimum.

I couldn't find statistics for how hot a mailbox gets but I did find well researched stats for something similar- cars.

A car in the sun is basically a small greenhouse on wheels and can become significantly hotter than the exterior. In similar temperatures cars parked in direct sunlight reached an average of 116F (47C). This is significantly less than required to bake bread.

There is no reason a mailbox would be more effective- it has no glass to create a greenhouse effect.

If mailboxes were that hot, we'd know

If a mailbox did reach 300F, it would be obvious. At that temperature paper singes and plastic deforms. Certain substances will combust or explode. The box itself would burn any mailman who touched it.

"Journalists" wouldn't be tweeting about bread- they'd be Tweeting about exploding mailboxes.

Answer 2

No. According to media reports, the woman in the picture has stated that the photo was staged, and intended to be a joke:

If the story is too good to be true, it's because it is. Roberta says while she shared photos of herself baking bread in the mailbox, it was all in fun.

"I believe some people believe that," Wright explained. "It's not exactly what happened. It's the storytelling of your imagination." (ABC13 Houston)

It seems, though, that the bread was indeed in the mailbox for at least some time during the preparation process:

"So technically, I proofed it in the mailbox and then I finished baking it inside," she said. "My daughter was telling me to be careful how I was saying this because I didn't technically bake it inside a mailbox, but I just loved the illusion."

The term "proofing" in breadmaking refers to the point at which you allow yeast to ferment the dough, causing it to rise. Once risen, a baker then pops it in the oven. There's a big range of temperatures for proofing bread, from 50 degrees Fahrenheit all the way to 110. (chron.com)

So while the temperature inside of the mailbox may be high enough for proofing bread, it's certainly not high enough to actually bake it.

Also note that the media reports usually don't fail to mention that the woman in the picture has recently published a children's book that seems to play with the topos of the quirky grandmother, so the whole story is very much on-brand. One thing that we can be sure is that the picture going viral will not hurt the sales of said book.