4 ms·

The thermodynamic argument is wrong. The radiant energy only depends on the temperature of the enclosure, not on its size. For example, if the diameter of the o

The thermodynamic argument is wrong. The radiant energy only depends on the temperature of the enclosure, not on its size. For example, if the diameter of the oven doubles, then each surface unit of the oven transfers energy to the dough at a rate 4 times slower, but there are 4 times as many surface units. The result is that the total energy flow dies not change.

colanderman 9y ago
I'd believe it if the Dutch Oven were made out of a higher emissivity material than a standard oven. But I think they're both porcelain-coated.
- deleted 9y ago
  [deleted]
- occamrazor 9y ago
  I think that, at typical oven temperatures, both can be approximated well enough by black bodies.
ouid 9y ago
This is pretty basic, and I'm surprised Kenji made such an error, given that he could easily have asked someone. I'm pretty sure that a dutch oven simply allows for more humidity in the air in contact with the dough, which allows that air to be hotter, without drying out the crust. In other words, the same mechanism that commercial bread ovens use to make bread.
djrogers 9y ago
I don't believe you're characterizing his thermodynamic explanation accurately - he's simply pointing out that the distance from the source of thermal radiation matters. Since radiant energy follows the inverse square law, this makes perfect sense.
- ouid 9y ago
  if there were exactly one point source of radiation it would matter, but there isn't. You have to integrate the cumulative radiation from all the points on the surface. The number of points in a subtended angle goes up as the square of the distance from the bread, and each points' contribution is the inverse square of that distance. This is true uniformly over any subtended arc, so the shape can't matter either. The result only depends on the emissivity of the material.
- kwillets 9y ago
  For a point emitter it's 1/d^2. For a plane it's 1/d^0.
f2f 9y ago
are you considering that the no-knead recipe calls for preheating the enclosure, and then gives additional tips to get the temperature even higher than the maximum possible in a given oven (for example turning the broiler on and leaving the door open, etc). that cast iron pot is _hot_ by the time the dough gets in.
skunkworks 9y ago
I'm a bit confused -- I think the point Kenji is making is that the lid as a radiant heat source is much closer than the top of the oven.
- URSpider94 9y ago
  It doesn't matter, because the fact that the walls of the oven are farther away is compensated by the larger surface area. It's invariant.
hinfaits 9y ago
Alternatively, decreasing the size of the oven wouldn't make a difference. If that was the case, this recipe would work in a small toaster oven. The inverse square law is factually sound, but incorrectly applied. My intuition would speculate the recipe works because the dutch oven is a "better" black body than the oven. So the dutch oven acts as a huge heat sink and then more efficiently retransmits by radiation that energy to the bread. As a secondary effect (or maybe this is the primary effect), the dutch oven promotes significantly more heat transfer primarily through conduction to the bread.
- occamrazor 9y ago
  Conduction through the bottom of the pot, which is in direct contact with the bread, might be an important part of it. However, if the heat transfer is much more effective, why doesn't it burn the bottom side?
  - kwillets 9y ago
    Porcelain is a big part of it. Baking stones are designed to balance specific heat and conduction so that you don't just end up with a burnt crust on a ball of raw dough. I couldn't get the recipe to load -- is the loaf put into a hot pan, or is the pan heated with the dough? In the latter case the whole cooking process is slowed down to allow the dough to rise a bit extra before it starts cooking.
    - MegaDeKay 9y ago
      The loaf is put into a preheated pan. I typically preheat for 30-35 minutes.
  - ouid 9y ago
    It did, for at least one of the commenters. However my theory is that the dough itself conducts heat better the denser and wetter it is. The bottom of the dutch oven transfers the heat very quickly, but also right at the beginning, when the dough is densest and wettest. by the middle of the cooking time, when the dough is likely to burn, it is actually the coldest part of the pot.
hinfaits 9y ago
Alternatively stated: decreasing the size of the oven wouldn't make a difference. If that was the case, this recipe would work in a small toaster oven. The inverse square law is factually sound, but incorrectly applied. My intuition would speculate the recipe works because the dutch oven is a "better" black body than the oven. So the dutch oven acts as a huge heat sink and then more efficiently retransmits by radiation that energy to the bread. As a secondary effect (or maybe this is the primary effect), the dutch oven promotes significantly more heat transfer primarily through conduction to the bread.

colanderman 9y ago

I'd believe it if the Dutch Oven were made out of a higher emissivity material than a standard oven. But I think they're both porcelain-coated.

deleted 9y ago
[deleted]
occamrazor 9y ago
I think that, at typical oven temperatures, both can be approximated well enough by black bodies.

ouid 9y ago

This is pretty basic, and I'm surprised Kenji made such an error, given that he could easily have asked someone. I'm pretty sure that a dutch oven simply allows for more humidity in the air in contact with the dough, which allows that air to be hotter, without drying out the crust. In other words, the same mechanism that commercial bread ovens use to make bread.

djrogers 9y ago

I don't believe you're characterizing his thermodynamic explanation accurately - he's simply pointing out that the distance from the source of thermal radiation matters. Since radiant energy follows the inverse square law, this makes perfect sense.

ouid 9y ago
if there were exactly one point source of radiation it would matter, but there isn't. You have to integrate the cumulative radiation from all the points on the surface. The number of points in a subtended angle goes up as the square of the distance from the bread, and each points' contribution is the inverse square of that distance. This is true uniformly over any subtended arc, so the shape can't matter either. The result only depends on the emissivity of the material.
kwillets 9y ago
For a point emitter it's 1/d^2. For a plane it's 1/d^0.

f2f 9y ago

are you considering that the no-knead recipe calls for preheating the enclosure, and then gives additional tips to get the temperature even higher than the maximum possible in a given oven (for example turning the broiler on and leaving the door open, etc). that cast iron pot is _hot_ by the time the dough gets in.

skunkworks 9y ago

I'm a bit confused -- I think the point Kenji is making is that the lid as a radiant heat source is much closer than the top of the oven.

URSpider94 9y ago
It doesn't matter, because the fact that the walls of the oven are farther away is compensated by the larger surface area. It's invariant.

hinfaits 9y ago

Alternatively, decreasing the size of the oven wouldn't make a difference. If that was the case, this recipe would work in a small toaster oven. The inverse square law is factually sound, but incorrectly applied. My intuition would speculate the recipe works because the dutch oven is a "better" black body than the oven. So the dutch oven acts as a huge heat sink and then more efficiently retransmits by radiation that energy to the bread. As a secondary effect (or maybe this is the primary effect), the dutch oven promotes significantly more heat transfer primarily through conduction to the bread.

occamrazor 9y ago
Conduction through the bottom of the pot, which is in direct contact with the bread, might be an important part of it. However, if the heat transfer is much more effective, why doesn't it burn the bottom side?
- kwillets 9y ago
  Porcelain is a big part of it. Baking stones are designed to balance specific heat and conduction so that you don't just end up with a burnt crust on a ball of raw dough. I couldn't get the recipe to load -- is the loaf put into a hot pan, or is the pan heated with the dough? In the latter case the whole cooking process is slowed down to allow the dough to rise a bit extra before it starts cooking.
  - MegaDeKay 9y ago
    The loaf is put into a preheated pan. I typically preheat for 30-35 minutes.
- ouid 9y ago
  It did, for at least one of the commenters. However my theory is that the dough itself conducts heat better the denser and wetter it is. The bottom of the dutch oven transfers the heat very quickly, but also right at the beginning, when the dough is densest and wettest. by the middle of the cooking time, when the dough is likely to burn, it is actually the coldest part of the pot.

hinfaits 9y ago

Alternatively stated: decreasing the size of the oven wouldn't make a difference. If that was the case, this recipe would work in a small toaster oven. The inverse square law is factually sound, but incorrectly applied. My intuition would speculate the recipe works because the dutch oven is a "better" black body than the oven. So the dutch oven acts as a huge heat sink and then more efficiently retransmits by radiation that energy to the bread. As a secondary effect (or maybe this is the primary effect), the dutch oven promotes significantly more heat transfer primarily through conduction to the bread.