Agriculture Reference
In-Depth Information
Table 19.4
Wheat grades and grade requirements.
Dockage, reported as a percentage, can also
include underdeveloped, shriveled, and small
pieces of wheat kernels removed during the
approved cleaning process. Grades are assigned
using numeric designations of US No. 1 for the
highest grade through US No. 5 for the lowest.
Any sample that fails to meet the criteria for US
No. 5, or has a commercially objectionable odor,
is designated as sample grade, or wheat of dis-
tinctly low quality.
Foreign material, shrunken and broken kernels,
damaged kernels, and total defects are important
in determining grade requirements for wheat des-
ignated as US No. 1 through US No. 5; these
materials negatively affect fl our yield and quality
and often are removed during cleaning.
An additional quality measure is test weight,
which is reported in pounds per Winchester
bushel (approximately 1.25 ft
3
) in the US and in
kilograms per hectoliter in many other parts of
the world:
kg hL
−1
= (1.292 × lb bu
−1
) + 1.419, for most
wheat, and
kg hL
−1
= (1.292 × lb bu
−1
) + 0.630, for durum.
Higher test weight (i.e., greater wheat mass in
the same volume) indicates better quality wheat
and suggests easier processing and greater fl our
yield. However, higher test weight does not
always translate into measurable milling yield
improvement, because test weight as a single
factor does not account for other important
factors. These may include kernel uniformity,
size, and shape, and kernel-to-kernel surface fric-
tion or other environmental factors that affect
compaction of wheat into the test device. As a
result, other measures have been developed to
help millers understand the milling quality of a
sample. These may include nongrade determi-
nates such as thousand kernel weight discussed
in a later section or other measures of wheat size
and weight determined by the single-kernel char-
acterization system (SKCS 4100, Perten Instru-
ments, Huddinge Sweden).
Because US grain grading standards focus on
physical characteristics related to milling quality
and, to some extent, storability, these standards
often fail to accurately assess the functional quality
Grades US No.
Grading Factors
1
2
3
4
5
Minimum limits of
Test weight (lb
bu
-
1
)
Hard red spring or
White club
58.0
57.0
55.0
53.0
50.0
All other classes and
subclasses
60.0
58.0
56.0
54.0
51.0
Test weight (kg
hL
-
1
)
Hard red spring or
White club
76.4
75.1
72.5
69.9
66.0
Durum
78.2
75.6
73.0
70.4
66.5
All other classes and
subclasses
78.9
76.4
73.8
71.2
67.3
Maximum percentage limits of
Defects
Damaged kernels
Heat (part of total)
0.2
0.2
0.5
1.0
3.0
Total
2.0
4.0
7.0
10.0
15.0
Foreign material
0.4
0.7
1.3
3.0
5.0
Shrunken and broken
kernels
3.0
5.0
8.0
12.0
20.0
Total
a
3.0
5.0
8.0
12.0
20.0
Wheat of other classes
b
Contrasting classes
1.0
2.0
3.0
10.0
10.0
Total
c
3.0
5.0
10.0
10.0
10.0
Stones
0.1
0.1
0.1
0.1
0.1
Maximum count limits of
Other material
Animal fi lth
1
1
1
1
1
Castor beans
1
1
1
1
1
Crotalaria seeds
2
2
2
2
2
Glass
0
0
0
0
0
Stones
3
3
3
3
3
Unknown foreign
substance
3
3
3
3
3
Total
d
4
4
4
4
4
Insect-damaged
kernels in 100
g
31
31
31
31
31
a
Includes damaged kernels (total), foreign material,
shrunken and broken kernels.
b
Unclassed wheat of any grade may contain not more than
10.0% of wheat of other classes.
c
Includes contrasting classes.
d
Includes any combination of animal fi lth, castor beans,
crotalaria seeds, glass, stones, or unknown foreign
substances.
