2

1) I would think that crisping the meat towards the end of the cook could result in drying the already cooked portion, specifically if the heat is turned up for the crisping process near the end.

What do you think? Is there science behind this?

2) Also, why do some recipes require you to roast with the meat tucked in aluminum foil? Then we're effectively steaming the meat. Is there an advantage to that, flavor-wise, or is it only to speed up the cooking process?

l3win
  • 889
  • 4
  • 15
  • 24

1 Answers1

0

Short answers:

  1. Browning after cooking through works better because the surface is already dry;
  2. Its to speed the cooking.

Both of your questions are all about the water, so it is important to understand how water influences the way that meat cooks.

Water, as is well known, boils (at sea level, anyway) at about 100 C / 212 F. What is not well known is that the amount of energy to take liquid water at just at 100 C to steam just at 100 C is comparatively very large. This energy (required to break the inter-molecular hydrogen bonds as water is a polar molecule) is called the enthalpy of vaporization.

In order for a water molecule to jump from the liquid at the surface of the food, into the free steam above its surface, it must absorb enough heat to "pay for" the ehnalpy of vaporization.

This means that when water evaporates, it actually cools the surface (which is why sweating works for people). Conversely, when steam condenses on the surface of the food, it warms the surface because the enthalpy of vaporization is metaphorically paid back.

This process ensures that as long as their is liquid water at the surface of the meat (including being replaced from the interior as fast as it evaporates), the surface temperature of the meat cannot exceed 212 F / 100 C.

In order for steak or any other meat to brown, it must be brought to temperatures on the range of 250 - 300 F, at least, for the Maillard browning reactions to happen at a reasonable pace. This cannot happen when there is free water left on the meat because the temperature will be too low.

So the best way to brown meat is after cooking it through at low temperature. The low temperature cooking will have dried the surface, and it will be relatively easy to brown the surface for good flavor. This will also lead to less over cooking at the surface.

A roast in the oven that is uncovered cannot obtain a surface temperature higher than 212 F so long as moisture from the interior flows to the surface and keeps it wet. The evaporative cooling will ensure this. This means that the heat conducting into the center is also limited to 212 F, and it may take a while to bring your roast to its desired temperature.

By wrapping the roast in foil, the steam evaporating from the surface is trapped close to the roast. Eventually, the vapor pressure inside the foil will be such that water condenses back onto the roast almost as fast as it evaporates, essentially shutting down the evaporative cooling, as condensing water returns the energy lost in the enthalpy of evaporation.

So the surface temperature of the meat can now climb above 212 F, and thus allow conduction of heat into the center of the roast more quickly, allowing it to cook through to the desired temperature more quickly.

Of course, this is at the cost of keeping the surface moist, so won't develop crust as well. This is why the foil is usually removed towards the end, so that the surface (which is quite hot) can now dry, and allow the delicious browning to proceed.

See also:

Community
  • 1
SAJ14SAJ
  • 72,735
  • 13
  • 153
  • 231
  • To summarize: It's best to cover the roast with foil and brown the skin after the interior has been cooked to an appropriate temperature – l3win Oct 23 '13 at 03:16
  • Do you recommend raising the temperature during the browning step at the end? According to your answer, depending on the size, 375-400 for a few minutes should be able to do it, depending on the size of the meat. – l3win Oct 23 '13 at 03:42
  • Yes, if you are browning a roast after it is already essentially fully cooked, you can take your oven up very high. 500 F is not out of the question. It is also not terribly size dependent, since the browning all happens at the surface. – SAJ14SAJ Oct 23 '13 at 12:50
  • But wait, since the foil is kept on, all the steam is kept inside the foil + pan volume, so there really isn't any way for the water to escape, so the surface will not be dry and completely ready for browning when the meat is fully cooked. – l3win Oct 23 '13 at 18:21
  • That is true, once you remove the foil the surface will have to dry before browning begins. But as considerable water will have been expressed (due to the contraction of the proteins as they went to well done), this will take less time than it would with a raw roast. – SAJ14SAJ Oct 23 '13 at 18:54
  • Following up on this: What if I roast at 200 F, below the evaporation point of water? Will it matter if I cover it in foil or not? Will it still save time? – l3win Feb 15 '14 at 21:11
  • Yes, the effect still occurs at low temperatures. See the Amazing Ribs link. – SAJ14SAJ Feb 15 '14 at 21:21