Environmental Engineering Reference
In-Depth Information
Box 7.1
Open-Fire Cooking of Meat: Wood Consumption
Realistic assumptions needed to set plausible maxima of phytomass consumption for
late Paleolithic cooking include the following: an average daily food energy intake of
10 MJ (that is, about 2,500 kcal, adequate for an adult and hence exaggerating the
average food need for an entire population), the meat share of this consumption at
80% (or 8 MJ, too generous for most cases, particularly when the meat would have
to come from smaller animals), the food energy density of a large animal carcass of
8-10 MJ/kg (typical for mammoths, but the rate is only about 5-6 MJ/kg for such
large ungulates as eland or elks), and an average ambient temperature of 20°C in warm
climates and a 10°C mean temperature in northern latitudes (needed to determine
energy needs to cook meat to desired doneness).
Furthermore, I assume that the temperature of meat when done would be 80°C
(77°C is generally considered sufi cient for well-done meat), that the heat capacity of
this meat is about 3 kJ/kg°C (relatively high because meat is mostly water, whose
specii c heat capacity is 4.18 kJ/kg), that a typical cooking efi ciency of an open i re is
just 5% (with the most likely range between 2 and 8%), and that the average energy
density of wood is 15 MJ/kg (this is the lower heating value, accounting for the fact
that a substantial amount of energy is needed to evaporate the water present in freshly
harvested wood). These assumptions result in a daily per capita intake of close to 1 kg
of mammoth (and about 1.5 kg of large ungulate) meat, and to cook it without any
energy losses would require roughly 200-300 kJ; with a 5% open-i re efi ciency, it
would take about 4-6 MJ of wood, or 1.5-2.2 GJ in a year, an equivalent of 100-150
kg of (some fresh and some air-dried) wood.
If the same fuel demand were to apply to every individual of some 200,000 people
who lived 20,000 years ago, the overall need would add up to 20,000-30,000 t of
woody phytomass a year (the generous assumptions made to calculate this total would
also take care of the fuel needed to cook the plant portion of the average diet, assumed
here to be only 20% of the total intake). This means that even if we assume a relatively
large late Pleistocene population, the aggregate demand for cooking fuel amounted to
only a negligible share of terrestrial primary productivity and to an even smaller share
of the standing woody phytomass: its estimated preagricultural total (see chapter 1) is
more than 100 million times larger.
