A mixogram is conducted with 10g of flour and the appropriate amount
of water to give optimum absorption. The mixograph is a recording
mixer reflecting the resistance of the dough during mixing. Most
mixograms are run 5 to 8 minutes, which is sufficient time for most
flours to exhibit their mixing time to peak and dough breakdown.
Dough breakdown behavior is reflected in the tail of the curve when
mixing continues beyond the mixing peak and is commonly referred
to as mixing tolerance. The mixogram is used to characterize new
selections as to market class and to predict baking properties.
For desirable bread-type flour, from Hard Red and White, Winter
and Spring selections with adequate flour protein, a mixogram should
have the following properties: high water absorption, moderately
long mixing requirements (3-6 minutes), strong gluten strength,
good dough mixing tolerance, minimum oxidation requirements. Good
dough mixing tolerance, as seen on the mixogram would indicate that
a bread dough should be elastic after mixing. Extremely long mixing
time is considered undesirable because the power and time requirements
would be excessive in a commercial bakery. In addition, extremely
long mixing time is often associated with tough, bucky doughs which
do not perform properly in a mechanized bakery.
Desirable pastry and confectionary flours (i.e. non bread-type
flours) from Common Soft White and Club, Winter and Spring selections,
should be soft, velvety and low in protein content. Their mixograms
should have the following properties: low water absorption, short
mixing requirement and no appreciable development with continued
mixing, i.e. the mixing curve area should be low, showing
weak and very mellow gluten strength. Club wheat flour should have
lower water absorption and weaker mixing properties and gluten strength
than the Soft Common wheat flours.
The mixograms are visually evaluated for gluten strength and mixing
properties. Mixogram absorption (MABS)
is optimum flour water absorption and is reported as per cent by
weight, corrected to a 14% flour moisture basis. MABS
is a function of protein content, variety, flour moisture and environment.
For bread-type wheat flour, MABS
is used to estimate the bread baking absorption (BABS).
The mixogram mixing time (not reported) is used to estimate the
optimum bread dough mixing time (MTIME).
Mixogram curves of bread-type flours with undesirable traits (low
flour protein, short mixing time, poor mixing tolerance, weak gluten
strength and low water absorption) are often eliminated from further
testing, i.e. bread baking, in the hurdle (screening) process.
Generally, a single undesirable property for any one of the important
mixogram properties is sufficient to classify a selection as undesirable.
Final evaluation must be made with consideration to the protein
content of the flour due to the effect of protein content on mixing
characteristics even within the same variety. As protein increases,
mixing time will decrease. This is illustrated on the Mixogram
Reference Chart. Compare #1 high(H) with #2 medium (M) and #3 low(L)
which are typical mixograms of the club wheat Tres at 12, 9 and
6% protein, respectively. Similarly, 2H, 3M and 4L are typical
for Stephens at these protein levels. Little change can be observed
on any wheat above 13.0 or below 7.5% protein.
The Mixogram Reference Chart is used to identify the curve characteristics
which most closely match the sample chart identifiers, i.e.
1L, 1M, 1H, etc. through 8H and are reported as Mixograph Type (MTYPE).
Desirable mixogram characteristics of bread type flours would be
characterized on the Reference Chart as high (H) Mixogram type (MTYPE)
with preference ranging from 3H to 6H. Desirable mixogram characteristics
of non-bread type (pastry flours) would be characterized on the
Reference Chart as low (L) or medium (M) Mixogram Type (MTYPE).
Preference would be for mixograms in the low (L) category. As described
above, this is dependent on protein content.
|The Wheat Analysis System [WAS; (13),(14)]
grades the experimental lines in comparison to a check(s). The
system relies on nursery "checks" (standards) and historical
standard deviation "windows". The mean of the nursery
standards is used to "center" the window. Experimental
lines with values that lie within this window are not flagged.
Lines with values that lie outside the window are flagged accordingly:
"-" for 1 to 2 s.d. poorer than the standard mean, "-2"
for 2 or more s.d. poorer than the standard mean, "+"
for 1 to 2 s.d. better than the standard mean, "+2" for
2 or more s.d. better than the standard mean. Note also that lines
are scored based on desired quality, e.g. greater
ash values give increasingly negative scores (lower ash is
preferred) and protein is scored according to whether the market
class is hard or soft. Those cultivars used as standards are indicated
with an "*" immediately to the left of the SAMPLE
Below the nursery data is a single line which keys the standards
(*), lists the mean flour protein for the entire nursery, and describes
the type of mill used for flour milling (Buhler, Quad or Short-Quad).
Below this line are statistics generated by the computer grading
system. They are listed by class. Included here are the mean values
for the standards (SM) and the means and standard deviations for
the experimental (NM and NSD respectively). (Note that "check"
varieties not marked as standards are treated as experimental).
Note too, that standards are not necessarily "class-specific".
For example, if there are no check varieties in the HWS, WAS will
prompt for the class of check variety to compare to (13),(14).