Environmental Engineering Reference
In-Depth Information
adapted to harvest sweet sorghum. The primary advantage of this approach includes the rapid
loss of moisture in the first 24 h after chopping. In-field juice harvesters expel the sugar-rich juice
during harvest and can thus eliminate the cost of transporting stalk material. This approach may
also permit the use of low-cost, on-farm fermentation as an alternative to large-scale processing/
fermentation facilities. A prototype juice harvester has been successfully demonstrated with sweet
sorghum varieties. The juice needs to be extracted to reduce the cost of transportation and speed-up
the drying of the stalks. The stalks contain from 40 to 50% moisture after extraction, depending
on the efficiency of the extraction process. The disadvantage of extracting the juice before burning
is that it reduces the Btu per pound by approximately 5-8%.
19.9.1 f actorS a ffEcting J uicE p roduction
Sugar content was highest in the middle of the plant stalk for sweet sorghum (Janssen et al. 1930).
The top 300-450 mm of the stalk could be removed without significant loss of juice and sugar. Plants
expressed 3 days after harvest and stripped of their leaves had higher sugar contents in the juice than
those expressed immediately after harvest (Janssen et al. 1930). Other experiments have shown that
juice yields decreased and sugar contents increased for sweet sorghum stalks stored 48 h between
harvest and expression (Broadhead 1972). The change in sugar content and juice yield after storage was
attributed to evaporation of water from the plant in both cases. Juice yields from plants are also affected
by the amount of moisture in the soil (Janssen et al. 1930). The amount of solar radiation received by
sweet sorghum is responsible for 75% of the variation in plant crop yield (Hipp et al. 1970). The top 300
juice yields from plants are also affected by stalk, and juice yield increased linearly as the amount of
solar radiation received between the boot and early seed formation stages increased. Row spacing had
a highly significant effect on the fresh mass of the stalk and total plant of Rio variety sweet sorghum.
Fresh plant mass yields were higher for narrow row spacing. Sweet sorghum planted in a narrow-row
spacing had a greater leaf area compared with wide row spacing (Wortmann et al. 2010).
19.9.2 p otEntial u SES of S wEEt S orghum J uicE
There are a number of uses of sweet sorghum juice:
1. Sweet sorghum syrup has been produced in the United States since colonial days. Some
sweet sorghum syrup has at one time or another been produced in every one of the con-
tiguous 48 states. Sweet sorghum is grown extensively for syrup production in the south-
eastern states. Kentucky is one of eight states in the Southeast and Midwest producing
approximately 90% of the total U.S. output. Excellent quality syrup could be made when
the brix of raw juice was at least 14°C, which was more or less throughout the year. The
prepared syrup generally has a final brix of 70-75°C (corresponding to syrup temperatures
of approximately 106°C) and a minimum shelf-life of 6-9 months.
2. Ethanol can be produced from sweet sorghum juice using yeast. Immediately after har-
vesting, the fermentation process must begin. Fermentation can take place in large storage
containers in the environment without temperature control.
3. Sweet sorghum juice could be returned back to the soil to provide nutrients. Each 1000 gal
of juice contain 10 lb of nitrogen, 10 lb of potassium, and 10 lb of phosphorus, in addition
to micronutrients.
19.10 conclusIons
S. bicolor , a diploid, has a relatively small genome (735 Mbp), which although larger than rice
(389 Mbp) is smaller than the other important cereals (wheat 16,900 Mbp and maize 2600 Mbp). The
last genome duplication event for the S. bicolor genome seems to have occurred much earlier than
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