This past weekend was a busy one at the Sebastopol Demonstration Energy Garden. After a summer of soaking in sun and filling their stalks and seeds with sugars and starches, our Dale Sorghum crops went full cycle. From the 212 sq ft. that we had under cultivation we harvested 9 kg of dry seed and 115kg of sugar rich stalks. From the stalks that we harvested in addition to the 110 kg of stalk that were donated to us by Live Power farms (225 kg in total), we produced 10 gallons of sorghum juice. Of the 10 gallons produced, we fermented 8 gallons and with the other two produced approximately 57 oz of sweet sorghum syrup; this demonstrates the multiple possibilities that the crop offers. In addition we were able to utilize the carbon in the pressed stalks by adding what we didn’t use as a layer in our sheet mulch as an ingredient to our compost piles. The chickens quickly consumed the fresh leaves that topped each pile.

It took three of us approximately three hours on Friday to harvest the stalks and seeds; this includes removing the leaves from the stalks. The process entailed one man cutting the stalks at their base with a pair of hand held clippers while another tied the stalks in bundles and removed the seeded florets which were processed by a third. The seeds were separated and laid thin upon screens in the sun to be dehydrated and the stalks were stacked in the shade to be pressed the next day.

To press the stalks it required three people an additional 3.5 hours of labor on Saturday. We used the Improved Chattanooga #12 to press the stalks and caught the juice in 5 gallon buckets; the juice that emerged was a pea green and contained 15% sugar by volume. By comparing the measured weights (lbs) of bundles of four stalks with the volume (mL) of liquid that emerged we determined that on average 162.3 ml of juice is produced for every 1 kg of stalk pressed.

Overall harvesting and processing the stalks required about 21 hours of labor. We produced 10 gallons at 15% sugar from the 225 kg of stalk that we pressed giving us a 22.5:1 ratio of kilograms of stalk for each gallon of juice produced.

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Data published in the Alternative Field Crops Manual reports yields of 10 ton/acre for Dale Sorghum, of which 70% is comprised of the stalk. This is synonymous to 6350.3 kg of stalk/acre, which would indicate that 282.24 gallons could be achieved for each acre of Dale Sorghum under cultivation. Seeing that the juice produced from pressing the stalks is 15% sugar, fermentation should yield 282.24 gallons of mash at 7.5% alcohol. This shows that from one acre of Dale Sorghum, 21.17 gallons of 200 proof ethanol can be produced; the theoretical yield that they indicate however is over 400 gallons/acre.

Data published by Morris J. Bitzer at Blairsville, GA, and Quicksand, KY shows yields of Dale Sorghum at 20 tons of stalk/acre, 20321.28 kg stalk/acre, double the yield proposed by the Alternative Field Crops Manual, whose data was compiled from Waseca, MN.

Data published by Oak Ridge National Labratory, acquired from 4 different test sites in Indiana and Alabama, reported yields of 22.2 Mg/ha (9.9 tons/acre), similar to that published by Alternative Field Crops Manual.

Data Published by Texas A&M Extension agronomist, Juerg Blumenthal said the highest yield he'd acheived was 12.4 tons of dry matter per acre with the production of 395 gallons of ethanol per acre.

No indication of the proof of alcohol produced was provided in any of these studies, but I do not see how it is possible to yield such high volumes per acre. In each case either the juice pressed from the stalks is of a higher sugar percentage, their method of pressing is more efficient, or the sorghum is being grown in higher densities; none of this information was provided. Somehow, in each case, higher volumes of ethanol per acre were produced from lower masses of stalks per acre

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Proposed yields of sorghum stalk/acre: 10 ton/acre, 12.4 ton/acre, 22.2 Mg/ha (9.9 tons/acre), 20 ton/acre

Average = 13.075 ton per acre

1 acre = 43559.46 sqft

Harvested 212 sq ft = 0.005 acre

0.005 * 13.075 = 0.065 ton/acre

1 ton = 907 kg

Harvested 115 kg stalk = 0.127 ton stalk/0.005 acre = 25.4 ton stalk/acre

*25.4 tons stalk/acre being grown on site > 13.075 ton/acre proposed yield

Proposed yields of ethanol/acre: 400 gallons of ethanol/acre, 395 gallons

Average = 397.5 gallons ethanol/acre

Produced 10 gallon juice from 225kg stalk, of which 115 were grown on site

115/225 = 0.51 * 10= 5.1 gallons juice produced from grown sorghum

1 acre/0.005 acre = 200 * 5.1 gallons of juice produced = 1020 gallons of juice/acre

15% sugar will ferment to 7.5% ethanol

1020 gallon juice/acre * 7.5% ethanol after fermentation = 76.5 gallons ethanol/acre

*76.5 gallon of ethanol/acre produced < 397.5 gallon ethanol/acre proposed. This data correlates more with the projected 21.17 gallons of ethanol/acre that I proposed based on the obtained 22.5 kg stalk:gallon juice ratio and the assumption that starting with a 15% sugar content will produce a 7.5% alcoholic mash after fermentation.

Heres a video of Sorghum Syrup being made at Kentucky State University.

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As the crops grow, we are racing to equip the garden with the tools required for the production of ethanol as a fuel source.

Ethanol Production

1. Fermentation

To produce ethanol from the crops that we are growing we must first mascerate and press the sugar/starch rich part of the plant into what is called the wort.

By bringing the wort to a boil in a stainless steel kettle we are able to kill off the bacteria and other microbes that would compete with the distillers yeast that we introduce once the wort has cooled down. The quicker the cooling process the better; this reduces the risk of bacteria reestablishing residence in the mixture. Once the yeast has been added the contents of the kettle are refered to as the mash. It is the mash that we add to our airtight fermentation containers and allow to ferment for 1-3 days.

Before adding the yeast it is important to check the temperature of the mixture. Yeast prefers temperatures of 80-90 degrees farenheit.

Before adding the yeast it is important to check the sugar content of the mixture. Because yeast converts about half of the sugar to alcohol (the other half into CO2) and because yeast commonly perishes in alcohol percentages of 15% and higher, it important to dillute your wort to sugar percentages of 20-30%. By adding cooled sterilized water you can quickly cool the wort while reducing the sugar content.

C6H12O6 → 2CO2 + 2C2H5OH

Before adding the yeast it is important to check the pH of the mixture. Yeast performs best at a slightly acidic pH of 4-4.5. By using lithmus paper and adding an acid or base accordingly this pH can be obtained.

Yeast can be added once the mixture meets these conditions. Allow the mash to ferment for three days before disturbing the anaerobic process.

2. Distillation

After fermentation the mash should have an alcohol percentage ranging from 10-20%. So as to obtain the higher percentages required for running a vehicle distillation is necessary. Using a reflux still, obtaining alcohol percentages up to 95% is possible. The remaing 5% water can be removed using zeolite or corn grain as a filter. Constructing a still and obtaining our experimental distillers license is the next step in our goal of producing fuel from the crops that we are growing at the Sebastopol Demonstration Energy Garden.