Agriculture Reference
In-Depth Information
the seeds, allowing seeds tested in
L
-DOPA to be
planted if required. Problems with PPO-related
darkening are not specifi cally related to prehar-
vest sprouting. However, increases in PPO activ-
ity (Kruger and Reed 1988) and the putative
increase in soluble phenolic substrates (Edwards
et al., 1989) during germination are an undesir-
able combination.
for further specifi c guidelines. According to
Posner and Hibbs (1997) test milling needs to
depict accurately the ease of separation of the
endosperm, germ, and bran, the level of admix-
ture of bran in ground endosperm, and the parti-
cle-size distribution of the fl our. They also suggest
that test milling should depict the fl ow of the mill
stocks that would give some indication of sieving
ease, although the latter is diffi cult to ascertain on
small test mills.
There are a few important milling parameters
that one can observe using a test mill. For example,
overall fl our yield, break fl our yield (the amount
of endosperm material of fl our particle size
released from the fi rst break roll), fl our ash (AACC
approved method 08-01, AACC 2000; see follow-
ing section), fl our color, and particle-size distri-
bution are elements of milling performance that
can be compared across cultivars or blends. Breed-
ing programs arguably focus on the fi rst three
elements, fl our yield, break yield, and ash. The
emphasis changes depending on whether soft
wheat or hard wheat is being milled. For soft
wheat break fl our yield is emphasized. For hard
wheat total fl our yield is the fi rst parameter taken
into account. Flour ash is important in both
instances. Candidate cultivars from several pro-
grams entered in the Pacifi c Northwest Wheat
Quality Council are milled on a Miag pilot scale
mill, where cumulative ash curves from 15 mill
streams are generated. This type of analysis is a
better indicator of overall milling quality, showing
the ash contents of each mill stream. The sharp-
ness of the corner of the plot where the fl our
streams transition to the shorts, “red-dog”, and
bran streams are an indicator of the relative ease
of separation of bran and endosperm (Fig. 20.2).
Sharper corners are more desired because they
indicate retention of low ash levels as far as pos-
sible before the ash levels increase sharply at the
offal streams.
Test milling
The milling properties of wheat are fundamental
to the great majority of wheat uses in the world.
Commercial millers have considerable control
over the characteristics of the fl ours they produce.
This begins with their choice of wheat classes. In
some cases millers are able to choose both market
class and region of production in order to get
specifi c attributes such as restricted protein range,
or regional selection might enable millers to limit
or control the number and identities of cultivars
in the grain lots they purchase. Millers also control
the wheat blends (grists) they apply to the mill.
Millers can also choose the type of mill fl ow, as
well as roll speed, speed differentials, disposition
of fl uted rolls (e.g., sharp to sharp), and roll pres-
sures in smooth reduction rolls. Further choices
are available in the combinations of sieves and
purifi ers, and fi nally in the mill stream selections
used to blend the fi nal fl our. All these strategies
help millers to consistently produce fl our with the
desired qualities. Small-scale test mills have
nowhere near the fl exibility, but that may be a
blessing when setting up standard test milling
protocols.
Posner and Hibbs (1997) make a distinction
between small laboratory-scale mills with preset
roll gaps and roll speeds, and simple sifting
schemes, versus larger experimental mills. The
larger mills allow operators to have some control
over the mill settings and the mills have more
complex sifting schemes in order to optimize, as
far as possible, the mill settings for the type of
wheat being milled. Interested readers are encour-
aged to read Posner and Hibbs (1997) for a com-
prehensive review on experimental milling as well
as AACC approved method 26-10A (AACC 2000)
Grain and fl our ash
Ash is the mineral or inorganic residue left after
burning wheat or fl our at 500-600 ºC for as long
as needed to completely oxidize all the combusti-
