Banjo's Insight - Searing the meat to lock in juices

A lot of old cooking and grilling references will tell you to "sear the meat to lock the juice/moisture in".  This is hogwash.

But I don't want you to just take my word to this - I want to lead you through a thought process that will prove to you this is hogwash.

I know that you already know that if you heat something, it expands (except ice heated up until it melts to water - it shrinks in size).

A piece of meat is made up of lots of cells.  Each cell contains fluids, which are held in by a cell membrane.

If you have a piece of meat, and you heat it up, then the fluid in each cell is going to expand as it heats.  Ultimately, this expansion will be too much for the cell membrane, and the membrane will rupture, allowing the fluid to escape out of the cell.

Fluids flow from high pressure to low pressure (well, anything actually moves from a point of high pressure to low pressure, not just fluids, providing you apply enough pressure to overcome the resistance holding the item in place).  Heating a fluid creates a higher pressure in the fluid, so it both expands out of the membrane, and flows out of the meat (which is heated and therefore at a higher pressure) into the surroundings.  So the fluid is going to flow out of the meat.

Since all of the meat is being heated, all of the muscle fiber (which is what meat is) is expanding, so there's no where for the fluid to go except to go out of the meat - it's sort of like you squeezing a water-soaked sponge - the fluid is going to be forced out of the sponge.

When you 'sear' the outside of the meat, all you are doing is heating the cells on the outside surface to a high temperature much faster than the cells deeper within the meat are being heated.  This means the outside cells next to the heat source are going to rupture first, spilling their fluids.  This fluid will evaporate in the high heat, leaving behind any non-water substances that will stay on the meat; these will brown (Maillard Browning).

However, these browning substances aren't water tight - they will actually dissolve in water.  If you heat the meat up enough, all of the water will flow out of the meat, and the meat will be dry, dry, dry.

As the interior of the meat heats up, the meat will heat up and expand, those cells will rupture, and you get the same reaction as squeezing the sponge - the space holding the water (the meat) is expanding, forcing (wringing) the water out of the cells, and out of the meat.

So searing doesn't "seal in the juices".  It does, however, cause the browning, which increases the flavor.

So we sear to increase the flavor.