One of the things
often said in BBQ is that meat "stops taking smoke" at 140 degrees. I
was curious about this, especially considering that it is possible to "over
smoke" meat. If the meat stopped taking smoke at 140, how was it
possible to over smoke it? The "smoke ring" is frequently used as a measure
of good BBQ. What did it have to do with the smoke flavor? I did a little research and came up with the
fact that the smoke ring and smoke flavor are 2 different things.
The smoke ring is a chemical reaction produced by nitrates/nitrites (and
carbon monoxide in smoke). These compounds react with hemoglobin/myoglobin in
the meats to produce the color you see. At a certain temperature,
hemoglobin/myoglobin denature (cook) so that reaction stops. This reaction can
even occur with gas if the gas is incompletely combusted or contaminated.
"Surface
pinking, also termed “pink ring” can occur if
gas ovens or barbecue grills are used to cook meat
products. Incomplete burning of the gas or
contaminates in the gas result in the formation of
nitrogen dioxide and nitric oxide. Nitric oxide is the
active form of nitrite that yields the pink color."
Ref:
Meat Color
The temperature at which myoglobin denatures is variable. Increasing the pH
increases the heat stability of myoglobin. This temperature can range from 104
to 160 Fahrenheit. Starting with a cold piece of meat and raising the
temperature slowly gives a more intense smoke ring because myoglobin has more
time to convert before it denatures. Once it denatures, the smoke ring stops
forming. As best as I can tell, this is where the idea that meat "stops taking
smoke" at 140 comes from. The smoke ring does not affect flavor.
Ref:
Myoglobin 1
Ref:
Myoglobin 2
The smoke flavor depends on the compounds in the smoke. The compounds in the
smoke depend on the fuel and the efficiency of combustion. Inefficient
combustion produces dense white smoke. Dense white smoke
has a lot of creosote. Creosote makes the meat bitter and overwhelms other
flavors. The taste we perceive is mostly due to smell so the flavors we are
looking for are due to the
aromatic compounds in the smoke. Higher
temperatures (more efficient combustion) break down these compounds resulting
in less "smoke flavor." What aromatic compounds you start with also plays a
large part in what you end up with. Soft woods like pines are loaded with
turpentine like compounds so we don't use them. Mesquite is another example of
a strong flavor profile. A little goes a long way. This also explains why
green wood is so strong. It has a much higher amount of aromatic compounds (as
well as moisture which impedes efficient combustion) than aged wood. Over aged
wood burns more efficiently (less moisture) and the aromatic flavor compounds
have deteriorated yielding less flavor.
Because the "smoke flavor" is from the deposition of these compounds, the
longer the meat cooks in the smoke, regardless of the meat temperature, more
smoke flavor is deposited.