On food and cooking the science and lore of the kitchen ( PDFDrive ) 856

waterandcarbondioxide.
TheNatureofWoodWoodconsistsofthree
primary
materials:
cellulose
and
hemicellulose,whichformtheframeworkand
the filler of all plant cell walls, and lignin, a
reinforcing material that binds neighboring
cell walls together and gives wood its
strength.Celluloseandhemicelluloseareboth
aggregates of sugar molecules (pp. 265,266).
Lignin is made of intricately inter-locked
phenolic molecules — essentially rings of
carbon atoms with various additional
chemicalgroupsattached—andisoneofthe
most complex natural substances known. The
higherthelignincontentofawood,theharder
it is and the hotter it burns; its combustion
releases 50% more heat than cellulose.
Mesquite wood is well-known for its hightemperature fire, which it owes to its 64%
lignincontent(hickory,acommonhardwood,
is 18% lignin). Most wood also contains a


small amount of protein, enough to support
the browning reactions that generate typical
roasted flavors (p. 778) at moderately hot
temperatures. Evergreens such as pine, fir,
andsprucealsocontainsignificantamountsof
resin, a mixture of compounds related to fats

thatproduceaharshsootwhenburned.
How Burning Transforms Wood into
Flavor Burning temperatures transform each
of the wood components into a characteristic
group of compounds (see box, p.449). The
sugars in cellulose and hemicellulose break
apartintomanyofthesamemoleculesfound
incaramel,withsweet,fruity,flowery,bready
aromas.Andtheinterlockedphenolicringsof
ligninbreakapartfromeachotherintoahost
of smaller, volatile phenolics and other
fragments,whichhavethespecificaromasof
vanilla and clove as well as a generic
spiciness,sweetness,andpungency.Cooksget
thesevolatilesintosolidfoods,usuallymeats