THE MACADAMIA NUT IN HAWAII 3 
Table I. — Tree and nut characteristics of the rough-shell and smooth-shell types of 
macadamia nut 
Item 
Tree: 
Leaves 
Bark 
Wood .structure 
Susceptibility to insect* 
Age of initial tn-aririk? (seed- 
lings). 
Cnshelled nut: 
Shape 
Shell surface 
Shell tartan 
Raw kernel: 
Color 
Shrinkage 
Texture 
Quality 
Adhesion to shell 
Ko.i-t.M kernel: 
Color. 
Texture 
Flavor 
Rough-shell type 
Excessively spiny; young leaves 
pink to red in color. 
Light gray with many lenticels. 
WVak, resulting in much splitting 
of branches. 
Attacked by leaf rollers, mealy- 
bugs, grasshoppers, aphids, and 
nut borer. 
3 to 4 years 
Ovoid to elliptical 
Knobby 
Tough, coarse, and fibrous 
Darker kernel; grayish base 
Considerable 
Firm; not easily chipped or bruised. 
Variable 
Generally loosens readily. 
Dark brown 
Firm to hard 
Pronounce.!, sweei, variable . 
Smooth-shell type 
Somewhat spiny, young leaves 
usually green, rarely pink. 
Dark gray with fewer lenticels. 
Fairly strong; much less splitting. 
Damage negligible except for leaf 
rollers. 
4 to 6 years. 
Usually spherical. 
Smooth. 
More brittle. 
Clear, white kernel; usually light- 
colored base. 
Usually small. 
Tender; easily chipped and bruised. 
Generally superior and more uni- 
form. 
Often adheres. 
Light golden. 
Tender, crisp. 
Delicate, mild, uniform. 
While considerable differences exist within each type both as to 
tree and to nut characteristics, there is no difficulty in differentiating 
between the two. From the standpoint of a roasted product the dif- 
ferences are pronounced. In the raw state, the smooth-shell kernel 
has a rather flat flavor and mealy texture while the rough-shell kernel 
has a somewhat pleasing sweetish flavor and firm texture. Upon 
roasting, the smooth-shell nut develops a light-brown color, crisp, 
tender texture, and a delightful mild nutty flavor, while the rough- 
shell kernel darkens quickly and develops a somewhat burned variable 
flavor and harder texture. Public preference for the smooth-shell 
roasted nut is by no means universal, but because of the greater uni- 
formity in quality and more desirable field characteristics, the present 
trend is toward the smooth-shell type. 
While most of the commercial plantings are of the smooth-shell 
type, there is a sufficiency of the rough-shell, particularly in the Kona 
district, to necessitate its inclusion in this investigation. 
METHODS OF EVALUATING MACADAMIA NUTS 3 
INDIRECT METHODS OF DETERMINING THE OIL CONTENT 
The oil content is of importance in evaluating a nut, not only because . 
oil is the predominant constituent, but also because it serves as a 
I criterion of other qualities. Chemical methods of determining the oil 
content of various products are laborious and time-consuming so that 
rapid indirect methods have been developed; for example, the re- 
tractive-index method of determining the oil content of flax (2) and 
avocados (/), and the Babcock method of estimating the oil in pecans 
I (5 ). Specific gravity as an indirect means of determining variations in 
4 In the station investigation the nuts were brought to air-dry condition. This requires about 3 weeks in 
j a dry, wdi-\eutilated place. The air-dry moisture content of 3 to 4 percent permits cracking with a mini- 
mum of damage to the kernels. 
