Production of Syrup from Sorghum Bicolor

Melanie del Mar, Ryan Hoff, Robbin Monceaux, Tommy Nguyen, Lakshmi Sirigireddy04-18-2016

This paper describes the process of making a high quality syrup derived from a cereal crop called Sorghum bicolor. Sorghum is considered as an alternative to sugar due to the economic benefits and shows considerable market favoritism. There is a linear relationship between the processing and production costs for sugarcane which are higher. This unprocessed crop is taken and turned into concentrated syrup that can be used as an alternative to molasses. The focus of this paper is a combination of Kentucky-traditional and Madhura-traditional process in order to create sweet sorghum. The specific processes include milling and washing the stalks, settling the juices, filtering it through a plate and frame filter, and finally pumping the remains into an evaporator until the syrup only remains. In addition, the waste products of the combined processes are also included in order to provide a beneficial role in society such as being used as biofuels and feed for livestock.  

Table Of Contents

Objectives 4

Introduction 4

Process Considerations 4

Raw Materials 4

Enzymes 5

Bagasse and Leaves 5

Kentucky-Traditional 6

Madhura-Traditional 7

Modern 8

Chosen Method 9

Flowchart Description 10

Flowchart Description 11

Cost and Mass Balance 15

References 17

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Table Of Figures

Figure 1: Diagram of Leaves and Bagasse in Heating 6

Figure 2: Vertical Diagram of Evaporator 7

Figure 3: Design of Gasifier-Powered Furnace 8

Figure 4: General Flowchart of Chosen Method 9

Figure 5: Detailed Flowchart of Chosen Syrup Production Method 10

Figure 6: Milling and Washing 11

Figure 7: Settling Tank 11

Figure 8: Plate and Frame Filtration 12

Figure 9: Fluid Labyrinth Evaporation 13

Figure 10: Storage and Bottling 13

Figure 11: Biomass Gasification 14

Table 1: Cost of Equipment 15

Table 2: Enzymes, Fuel, and Water Cost 15

Table 3: Estimated Profit – Harvesting 16

Table 4: Estimated Profit – Purchasing 16

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Objective

This paper intends to illustrate the process needed to produce 10,000 L of sorghum syrup during the sorghum season. The material inputs are few, the raw sorghum stalks & leaves, water and various enzymes.

Introduction

Sorghum bicolor, or sweet sorghum, is a commercially grown annual grass crop grown in arid, warm climates. It was introduced to the United States in the first half of the 17th century from European and African seeds. This species has been historically grown to support molasses production as it yields a high amount of sugars. However, its popularity as a syrup has decreased in the 20th century as cane syrup is cheaper to produce and more widely used (Faulkner). The south, particularly Kentucky and Tennessee, still has a deep-rooted attachment to pure sorghum syrup and commercially produce it today. More recently, the high cost of sugar mixed with the demand for regional foods has caused sorghum syrup to slowly become more marketable.

This crop is an attractive choice for farmers, as it requires low nutrient and water inputs. It is generally grown in areas where there is little rainfall and the temperatures remain moderately warm year round (Undersander, et al). The recent surge of biofuel research has also renewed interest in this crop as it shows promise for being a cheaper alternative to “traditional” bio-fuel crops because of its high content of sugar (Duke).

The sugars of sweet sorghum are contained in the juices of the stalked and are generally extracted through crushing or squeezing. The sugary juice is then filtered into tanks where it is allowed to settle. The juice is then heated until it reaches the desired density. The syrup is drained, cooled, and strained. The final processing steps include sterilization and dispensing into the commercial containers. These containers should be airtight to prevent the sugars from fermenting. Typically 6-12 liters of raw juice will be used to produce one liter of syrup and approximately 750 liters of syrup can be produced from one acre of crop (Keupper). Process Considerations

Raw Materials

In all process designs on sorghum syrup production, the main input is the sorghum crop itself after being subjected to traditional methods of processing. The process is best detailed in Sweet Sorghum Production and Processing by George Kuepper. First the leaves are either completely stripped from the stalks of the harvested plant or allowed to wilt on the stalks over a period of 10 days. The stalks are milled after to release their juice which creates a bagasse which can be later used for Biomass Gasification or dried and used as fuel for a traditional pan furnace. The juice taken from the milling can be processed in several different fashions varying only slightly for the Kentucky-traditional boiling method. The three sorghum syrup production processes to be considered are the Kentucky-traditional method, the Madhura-traditional method, and Modern method.

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Another major consideration that must be factored within the process is that many of the byproducts of sorghum may be used in other significant processes. The juice from the stalks may also be used to create ethanol or the bagasse can be used as cattle feed or can be fermented into silage to produce biofuel. The process must find means of integration into an agricultural system by cycling or selling by-products with other systems or creating a closed system by finding a way to efficiently use all by-products.

Enzymes

Sorghum syrup production tends to be made naturally, but there are a few enzymes that may be used as a way to increase shelf life or create more syrup. Natural enzymes or fruit juice with high citric acid concentration may be added to make the syrup less likely to crystallize. Invertase can be added to slowly convert the sucrose build up into glucose and fructose making the syrup slightly thinner preventing crystallization. During the settling period of the process often if the sorghum juice is left in the tank for extended periods of time certain levels of fermentation will occur. Fermentation in excess during settling will ruin the whole batch of juice so α-amylase or β-amylase is often added to prevent this fermentation. These enzymes also prevent gelling which results from higher than normal amounts of starch in the raw juice. The enzymes break down the starch into sugars and dextrans. During the heating process, some beneficial naturally occurring enzymes in the sorghum juice are destroyed due to heat-degradation. These enzymes may be reintroduced during the final stages of the process to increase the amount of product overall. However there is an overwhelming argument against the addition of enzymes, which is the cost of the addition of these enzymes. The introduction of multiple enzyme cocktails during the process could cost more than the profit from the recovered juice or prevented crystallization. Therefore the introduction of enzymes must be carefully considered using cost analysis to ensure a balance between cost and product quality.

Bagasse and Leaves

Figure 1 shows a pictorial representation of the process design of Sorghum without the leaves, but Sorghum syrup can be processed two ways: with leaves or just the stalks. Excellent syrup can be made without stripping off the leaves due to the extra amount of juice it can carry. The conditioning of the stalks with leaves allows the sucrose to reduce more sugars and this helps improve the quality of the juice. Keeping the leaves on the stalks also decreases the amount of labor and time taken to remove the leaves. However, the stalks cannot be crushed when the leaves are not stripped in order to preserve the moisture and sugar content of the juice.

Bagasse is the remains of the crushed sorghum stalks with the leaves remaining. It can be used as biofuel, a substitute for wood, or feed for livestock. Bagasse can naturally also be used to create syrup with a little more effort. About 4-5 kg of the dry bagasse can be converted to making 1 kg of syrup. The energy output that bagasse provides can help the mills meet 100% of their energy needs. These facilities need to generate heat and electricity which can be done without having to worry about transportation and gas emissions.

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Figure 1: Rough Diagram of Madhura-method showing the use of leaves and bagasse in the heating process

Kentucky-Traditional

The Kentucky-traditional process in which sorghum syrup is made is outlined best in the article Processing Sweet Sorghum for Syrup by Morris J Bitzer and Joe D. Fox which was published by University of Kentucky’s College of Agriculture. The process begins by taking the juice created from the milling of the sorghum stalks and filtering it through a wire screen mesh serving to remove the much larger particulates such as stalk and leaf fragments. The juice, which is green in color, is again filtered through a finer screen and then allowed to settle within a tank for a few hours (no more than 3 to 4 as it may begin to ferment if left for that long). After allowing the juice to settle it is then drawn from slightly above the bottom of the tank and pumped into an evaporator. However, in larger batches during the settling process the juice may be subjected to light heat and enzymes such as α-amylase are added to help catalyze the breakdown of starch to sugar. The juice is also skim filtered in the larger batch settling process to further remove any suspended particulate plant matter.

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Figure 2: Evaporator vertical diagram detailing the “labyrinth” and heat source

Figure 2 shows an evaporator which is a labyrinth like tank that allows the juice to be subjected to heat for the longest time possible while slowly flowing to the end of the evaporator. There may be a skimming trough attached to the juice input side of the evaporator so that it is filtering as the juice is continuously pumped in. These “skimmings” are coagulated proteins and other non-sugar substances can be used for animal feed. After the juice has made its way through the evaporator, it has become the syrup desired. The syrup is immediately strained and then placed in a container for storage or sent to be bottled. Additionally, to the described process there are optional sub steps that can improve yield or product quality. For example, the juice can be pre-heated prior to the evaporating process which lessens the time for cook-off in the evaporator and reduces the amount of skimming needed to be done.

Madhura-Traditional

The Madhura-traditional process was described in the article Syrup Production from Sweet Sorghum by Nandini Nimbkar, N.M. Kolekar, J. H. Akade and A.K. Rajvanshi. It’s comparable to the Kentucky traditional method. The process again starts will milling described as “crushing” within the paper collecting the juice from the sorghum stalks. The juice is then pumped into a settling tank where it is allowed to sit for a few hours. The juice is then allowed to flow through a series of filters and then pumped into a large stainless steel vessel called a kadhai. The kadhai is similar in shape to a pan except much larger with capacity of 350-400 L of the juice. It functions as an evaporator as the juice is allowed to sit within the kadhai while subjected to heat allowing the water to evaporate off and syrup to form.

The heat for the evaporator is turned on after the juice has been pumped into the kadhai. The juice is then slowly heated while scum and other particulates are skimmed off the top of the juice. Once the juice has been warmed to a temperature of around 80-90 ⁰C okra fruit extract is added at about 1.5 kg per 300 L of Juice and then further scum removing occurs. After a few hours when the temp has reached 105-107 ⁰C the juice has evaporated off and become the syrup ready for storage or immediate bottling. However, the most novel portion of this process is not the method of boiling but the method of heating. The bagasse and leaves left over after the sorghum harvest are used in a biomass gasification system to heat the kadhai as shown in figure 3.

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Figure 3: Design of gasifier-powered furnace for sorghum syrup production

The bagasse is fed into the system to create the power at about 20-27% efficiency with the additional byproduct of char. The char may be mixed with any binder to form fuel briquetted for stoves or possible used as a soil conditioner for the sorghum fields. This novel form of generating heat creates another product for the batch cycle and removes the need to find use for the bagasse in alternative systems.

Modern

The modern relies on the most complex machinery and is more similar to an industrial refining process for sugar cane molasses. The extraction for the juice can be done via the traditional milling method however it can also be done via diffusion. In the diffusion method the stalks are placed in a hot water or lime (Ca(OH)2) bath and dissolved. The juice from the extractor is clarified by the addition of lime and CO2. The juice is pumped into a decanter and mixed with the lime while under heat. The clarified juice then runs through carbon filters which produce a mud-like substance. The juice past-filtering is called “carb-juice” which is then pumped through a heater and then to a clarifying machine. Within the clarifying machine the mud is allowed to settle so all the suspended particulates fall out of system. The juice is subjected to the clarifying process an additional time and then is pumped into an evaporator which boils of the water until only syrup remains. Unlike the traditional techniques there is no skimming during the boiling process due to the previous filtering.

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Chosen Method

The method we chose to use to produce our sorghum syrup follows the Kentucky method most closely but uses the biomass gasification method introduced in the Madhura method for heating the evaporator. The Kentucky method of sorghum syrup production was chosen due to its relative simplicity and the novel labyrinth evaporator, which we felt could be easily made at a larger scale. The biomass gasification system was chosen instead of other uses of the bagasse as it is most efficient to use the bagasse as a heat source instead of outsourcing it to biofuel production for a slight increase in revenue. A basic flowchart of our process is outlined in figure 4 with the detailed superpro diagram of the process in figure 5. A step-by-step explanation follows the superpro diagram detailing each sub step of the process with an explanation and pertinent inputs/outputs.

Figure 4. General flowchart for overall process9

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Figure 5. Detailed flowchart of chosen syrup production method

Milling and Washing

Figure 6: Flowchart created in SuperPro Designer depicting the process of milling and washing of sorghum stalks.

The 5500 bushels (192885L) of sorghum stalks are placed into a mill that crushes the stalks producing a mixture of juice and fragments of stalk and leaves as can be seen in figure 6. After passing through the mill the now crushed stalks are placed onto a conveyor belt where they are washed down with sprays of water. The water removes dirt and field debris during the earlier stage of washing however in the later stage of the washing the sprayed water helps free the sorghum juice absorbed by the leaves. Due to the washing process less sorghum juice remains absorbed by the juice and lost. We estimate that this washing will require 14,500L-17,400L of water or around 15% of the volume of the sorghum stalks. After the milling and washing process the 5500 bushels of stalks will yield anywhere from 77,154 L - 96,442 L of bagasse and 96,442 L -115,731 L of sorghum juice. With the addition of water the volume of liquid increases to 110,908 L -133,090 L.

Settling

Figure 7: Flowchart created in SuperPro Designer depicting the process of removing the solid plant waste from the sorghum juice.

The sorghum juice collected from the milling and washing step will still contain solid particles. To remove these particles suspended within the juice, the juice is allowed to settle

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within a tank in order for the remaining solids to accumulate and settle at the bottom of the tank allowing for their removal. Additionally, an amylase enzyme cocktail, similar in nature to what is used in beer brewing, will be added to ensure the breakdown of starches within the syrup. The mixture requires a minimum of three hours to settle before filtration, however it may not be allowed to settle over 24 hours to avoid fermentation. Once the sorghum juice has settled it is pumped out the top of the tank, while the particulate layer remains at the bottom to be later collected for repurpose. The remaining solid plant waste can function as animal feed or fermented into silage for creation of biofuel. The settling process can be depicted in figure 7. With a 7,500 L tank, our calculations call for a total of 18 batches to produce the 10,000L of sorghum syrup with the addition of 180mL of amylase enzyme cocktail to each batch, a total of 3.2L. This inspired us to include two 7500L tanks in our budget in order to cycle the milling and settling process to increase efficiency.

Filtration

Figure 8: Flowchart created in SuperPro Designer depicting the process of a plate and frame filtration.

Figure 8 shows the sorghum juice being extracted from the settling tank and then going through a custom 12 plate and frame filtration with a screen mesh of US size 45 (openings of 355 µm). As the sorghum juice passes through each plate the residual plant matter and unwanted particulates are caught by the filter creating the filter cake. This filter cake may be used similarly to the waste recovered from the settling step; for animal feed or fermented into silage for biofuel. Once the sorghum juice has passed through all of the plates the filtered juice moves to the evaporation step. After each batch the filter cakes will be removed and the filter will be flushed using water.

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Evaporation

Figure 9: Flowchart created in SuperPro Designer depicting the process of evaporation of the filtered sorghum juice.

The filtered juice should now be clean enough to be turned into syrup after having been

washed, settled and then filtered. To do so the filtered juice is placed into a fluid labyrinth evaporator (as seen in figure 9) that is heated to 105 ⁰C which allows for water from the juice to evaporate, concentrating the juice into a syrup. The evaporator will be designed in similar fashion to the one detailed in figure 9 with a larger scale. This evaporator is heated using the biomass gasification system which is detailed on figure 11. Along the top of the tank a skimmer removes any contents from the juice as the added heat will cause some remaining particles to rise to the surface. The juice will slowly thicken as water is removed from the system until the desired syrup consistency is formed. The evaporator will have to be staffed at all times while running as it must be manually skimmed as proteins will conglomerate on the surface and the heat must be carefully maintained to avoid burning.

Storage and Bottling

Figure 10: Flowchart created in SuperPro Designer depicting the process of storage and bottling of sorghum syrup

.The sorghum syrup is then placed into a storage tank in combination with a mixture of

enzymes that will stabilize the chemical activity of the syrup. This stabilization should yield a longer shelf for the product. A total of 1.6L of invertase will be used to produce the 10000L of

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sorghum syrup. The syrup is finally bottled at which point the product is ready to be distributed as can be seen at the end of figure 10.

Biomass Gasification

Figure 11: Flowchart created in SuperPro Designer depicting the process of biomass gasification.

Figure 11 shows the previously removed bagasse from the washing step which is placed into a grinder that produces small fine pieces of ground biomass. Air along with the ground biomass is pumped into the biomass gasifier which uses a small turbine to suspend the particulate biomass in the air. This biomass air will then be ignited using a natural gas pilot which will heat the biomass air which is pumped underneath the fluid labyrinth evaporator to heat it evenly. This process also creates char which can be combined using chemical binders to be used as charcoal or can be used at crop fertilizer.

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Cost and Mass Balance

Table 1: Cost of Equipment

Equipment Price Quantity Total12" plate and frame filter press $ 22.00 1 $ 22.0045 Mesh Wire $ 56.29 1 $ 56.298.5 oz. bottles $ 1.46 40000 $ 58,400.00Bottling Machine $ 5,000.00 1 $ 5,000.00Gasifier $ 15,000.00 1 $ 15,000.00Industrial Grinder $ 80,000.00 1 $ 80,000.00Labyrinth Evaporator $ 35,00.00 1 $ 35,000.00Settling Tanks $ 35,000.00 2 $ 70,000.00Storage Tanks $ 500.00 5 $ 2,500.00Washing Station $ 1,500.00 1 $ 1,500.00Total $ 267,478.29

The largest portion of the cost is due to the equipment involved in the process. However, most of these purchases are one-time. Table 1 shows that the industrial grinder and the labyrinth evaporator are the most expensive pieces of equipment. This is due to amount of customization needed to cater to the sorghum syrup process. The pricing of the pumps is not included because that will be determined based on the pipe size of the gasifier.

Enzymes, Fuel, and Water Price Per Unit Quantity TotalAmylase Cocktail $ 10.00 pound 66.043 $ 660.43Invertase $ 20.00 pound 60 $ 1,200.00Natural Gas $ 5.55 1000 ft3 850000 $ 4,717.50Water (Filtration) $ 0.03 10 gallons 8789.66 $ 2.59Water (Washing) $ 0.03 10 gallons 4585.93 $ 1.35Total $ 6,581.88Preparation Total $ 274,060.17

Table 2: Enzymes, Fuel, and Water Cost Analysis with Total Preparation Cost

For the pricing, all units have been converted to the English System. The amount of water used for washing is determined by the amount juice extracted. Assuming 42,485.68 gallons (high output) of juice is extracted from the 5511 bushels of sorghum stalks, 15% of the juice volume is needed to wash the crushed stalks. For filtering, 25% volume of the juice and washing water is added. The enzymes added to the syrup are invertase and amylase α or β. The amount of enzymes added need to be about 0.008 % of the total syrup volume. In this process, a total of

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approximately 0.172 gallons of enzymes is needed for the 2202.6 gallons of syrup created through the process. As seen in table 2, the cost of the water and enzymes is very small despite the quantity.

Table 3: Estimated Profit in Harvesting Sorghum Crops

Profit in Cultivating Price Per Unit Quantity TotalLand $ 365.26 acre 65 $ (23,741.90)Operating Cost $ 193.18 acre 65 $ (12,556.70)Labor $ 8.50 per worker per hour 3 workers $ (21,857.14)Preparation Total $ (274,060.17)Selling $ 10.00 bottle 40000 $ 400,000.00Profit $ 67,784.09

Table 4: Estimated Profit in Purchasing Sorghum Crops from Third-Party

Profit in Purchasing Price Per Unit Quantity TotalSorghum Crops $ 3.52 bushel 5511 $ (19,398.72)Labor $ 8.50 per worker per hour 3 workers $ (21,857.14)Preparation Total $ (274,060.17)Selling $ 10.00 bottle 40000 $ 400,000.00Profit $ 84,683.97

Tables 3 and 4 show the range of profit from processing and selling sorghum syrup. Growing the sorghum crops to be processed has an additional cost of owning and operating farmland in addition to the sorghum seeds. On the other hand, directly buying the stalks in bulk cuts the cost of producing the syrup. Actual expected profit is going to be less than the calculated numbers because this analysis does not take into account the additional unpredictable equipment needs, repairs, and maintenance. All in all, to maximize profit, it is better for the sorghum stalks to be purchased.

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