FRACTIONATION OF SUGARCANE FOR FEED AND FUEL
by
T.R. Preston

INTRODUCTION

When commercial production of sugar first began, the crop produced food for people, the fuel needed for processing and the feed for the animals used to transport the cane to the mill. Sugarcane processing remains a unique industry in not requiring exogenous sources of fuel, irrespective of whether the technology employed is industrial (crystalline sugar) or artisanal (“panela” or “gur”). The mules and oxen still used in many countries for hauling cane to the mill traditionally have been fed on the tops of the cane, the molasses and scums.

FRACTIONATION OF SUGARCANE

The extremely low fermentability of sugarcane fibre and the negative effect this had on voluntary intake of the overall diet was the reason for developing methods so that the juice and the residual fibre/sugar in the pressed stalk could be treated as separate entities.

This new approach to utilization of sugarcane for livestock feeding and fuel production was first developed in Mexico (Preston, 1980). The aim was to achieve only a partial extraction of the juice using simple low-cost cane crushers, of the kind developed for “panela” and “gur” production. This reduced the investment in machinery and the energy cost of milling (the stalk is passed only once through the crusher).

The justification for this system is that the juice carbohydrates (sucrose, glucose and fructose) are completely digestible by both ruminant and non-ruminant livestock and are thus viable alternatives for the starch in cereal grains. The tops of the cane and even the bagasse, which still contain appreciable amounts of sugars in the residual juice, have a potential digestibility of between 50 and 60 percent, and if adequately supplemented with fermentable nitrogen (urea or ammonia) have a nutritive value similar to Elephant grass. The bagasse can also be converted into charcoal (Ffoulkes et al., 1980) or producer gas (A. Lindgren, personal communication) or can be burned directly. It can also be fed to small ruminants which are able to select the sugar-rich pith, leaving the lignified rind as a source of fuel.

Sugarcane juice for ruminants

The fermentable carbohydrates in both sugarcane juice and molasses are sucrose, glucose and fructose. Molasses is the soluble residue after extraction of the sucrose from cane juice. Compared with cane juice, molasses is therefore richer in minerals, organic acids and other plant solubles.

Diets based on cane juice support much higher levels of animal productivity as compared to those based on molasses. The rates of growth and feed conversion efficiency recorded in studies with crossbred and zebu cattle in Mexico (Mena, 1986) are comparable with those recorded in intensive grain-based systems. Rumen microbial growth appears to be highly efficient on cane juice diets since the zebu cattle grew at 800 g per day on a minimum protein intake (5 percent protein in the diet dry matter supplied from leucaena) with the fermentable N provided by aqueous ammonia. This is in contrast to the average grain-based feeding system where at least 12 percent of the diet dry matter is protein.

It appears that on a cane juice diet, the end-products of rumen fermentation are well balanced and therefore support high animal productivity, much more than any other low-N diet. This indicates the extremely efficient microbial growth which must have supplied an almost ideal protein/energy ratio for production with minimum supplementation. Two observations on cane juice feeding should be emphasized, as they relate closely to the concepts underlying appropriate use of sugar-rich feeds by ruminants (Leng and Preston, 1986):

• Proprionate levels in the rumen were over 20 percent of the total VFA, considerably higher than on a molasses diet (Figure 1). Thus the glucogenic status of a diet of cane juice may be adequate for high growth rates.

• Protozoal biomass in the rumen was lower in animals fed cane juice than in those fed molasses (D. Harrison, personal communication) which will enhance the protein:energy ratio in the nutrients arising from rumen digestion.

Sugarcane juice for monogastric animals

The most appropriate commercial application for sugarcane juice is as the basis of a feeding system for monogastric animals. Traditionally in tropical countries these species have been managed as scavengers. When more intensive systems were introduced, imported cereal grains were the principal feed resources, thus competing directly with humans for food.

Sugarcane juice for pigs:

The research underlying the feeding of cane juice as the only carbohydrate source for pigs was initiated in Mexico and extended in the Dominican Republic where it has become the basis of commercial pig feeding systems on both large and small farms (Mena, 1986).

Cane juice has been shown to be a satisfactory carbohydrate source for all classes of pigs; however, its commercial usage is mostly in the finishing stage from 30 to 95 kg liveweight. Usually a commercial protein supplement (40 percent protein), fed on a restricted scale, provides all the amino acid needs; and the juice is given ad libitum.

Interesting developments (Mena, 1986), which promise to reduce feed costs, are that:

• protein levels in the finishing stage can be reduced to as low as 5 percent of the diet dry matter without apparently affecting performance

• protein-rich foliages from cassava and sweet potato can replace at least 25 percent of the protein in the supplement

• when cane juice is fed during pregnancy, birthweights and vigour in the newborn are increased.

Sugarcane juice for poultry:

Developments in the use of sugarcane juice as a grain substitute in poultry diets are still in the early stages; however, the preliminary findings are encouraging. Broilers in the finishing stage (from 1 to 2 kg liveweight) readily consume cane juice fed alone or dissolved in the drinking water. In the latter system the maximum rate of substitution was about 15–20 percent of the diet dry matter, possibly because additional drinking water was not provided and the birds became dehydrated (J. Montilla, personal communication).

Providing the juice and a protein supplement (39 percent protein) in separate feeders, both on a free choice basis, appears to be a more practical method. In this system, cereal grain is not fed but water is freely available. In a preliminary trial (Mena, 1986), intake of juice accounted for some 60 percent of total dry matter intake and performance levels were encouraging. Results from ongoing experiments in Colombia indicate that growth and feed conversion rates are only marginally inferior to those recorded on a conventional cereal-based diet (L. Possada and T.R. Preston, unpublished data).

Utilization of the residual pressed cane stalk

The maximum economic benefit from the use of sugarcane juice for livestock feeding will only be realized if technologies are developed to use the residual pressed stalk. The options being pursued for the use of this material include:

• feeding to large ruminants, especially draught animals
• feeding to small ruminants (sheep and goats) in a way that will permit a high degree of selection (e.g. by giving 200 percent of the normal dry matter intake)
• production of charcoal
• conversion to producer gas as a substitute for diesel fuel.

Converting the pressed cane stalk into a suitable material for gasifying requires sundrying to 80 percent dry matter and chipping into particules of 10–20 mm. A gasifier has been designed with specific characteristics to use dried sugarcane chips (A. Lindgren, personal communication). Making charcoal from pressed cane stalk is simple but requires briquetting to produce a readily saleable product (Ffoulkes et al., 1980).

A highly promising development is the use of the pressed (extracted) cane stalk as a basal diet for small ruminants. If the freshly pressed stalk is offered to goats, they consume avidly the sugar-rich pith and discard the lignified rind. In studies in the Dominican Republic goats on a mixed diet of pressed stalk and fresh gliricidia foliage selected and apparently preferred the pith to the green foliage (A. Mena, unpublished data).

EQUIPMENT FOR CANE FRACTIONATION

The juice is extracted from the sugarcane in a simple three-roll press, or mill, of the kind employed in the “gur” and “panela” industry. Extraction rates (expressed as weight of raw juice as percentage of weight of cane stalk) vary from 45 to 55 percent, depending on the construction of the press and the setting of the rollers. This is less than the current norms of producers of “panela” who regularly report extraction rates of between 60 and 65 percent. The difference can be explained in part by the fact that in “panela” manufacture, the residual bagasse is used as fuel for the boilers, while when cane is pressed for animal feed, the bagasse can be used as forage for ruminants, thus there is not the same economic pressure to maximize juice extraction, since the residual sugar in the bagasse increases its feed value.

ECONOMICS OF CANE FRACTIONATION

The economics of using sugarcane juice for feed and fuel production depend on the relative opportunity costs of cereal grain, sugarcane, protein supplements and labour. In most countries where sugarcane is (or can be) grown, cereal grain for animal feed purposes usually has to be imported (requires hard currency!) and the price is usually in the range of US$150 to 200/tonne. The opportunity price of sugarcane depends on many factors, among them:

• Is there an alternative market for the cane (e.g. a nearby sugar mill) and what is the transport cost?
• Is the country a sugar exporter, and to which market (e.g. EEC or free world market)?
• What is the opportunity value of the residual cane tops and bagasse?

Present prices in Colombia can be used as an example of the calculations that must be made. The opportunity price for sugarcane standing in the field is US$ 13.00/tonne for a contract with a sugar mill and US$ 10.00/tonne (no contract) when the buyer is a manufacturer of “panela”. The buyer in both cases assumes the cost of harvesting and transport to the mill. The cost of unskilled labour (minimum wage) is US$ 3.00/8-hour day which becomes US$ 4.50/day when social benefits are included; and the harvesting, transport (by mule) and processing (feeding the cane into the mill and forage chopper) require one work day (8 hr) per tonne of cane. Thus the products from one tonne of stalk cane (500 kg of juice, 500 kg of bagasse and 250 kg of cane tops) will cost US$ 17.20 assuming the opportunity cost of the cane stalk is the price paid by the factory.

If no use is made of the residual forage (bagasse and tops) then the price of the juice will be US$ 36.78/tonne fresh basis (equivalent to US$ 166.00/tonne grain of 10 percent moisture). On the other hand, if it is assumed that the residual forage from the sugarcane after juice extraction (bagasse plus tops) is fed to cattle and that its feeding value is half that of a forage crop such as Elephant grass then the cost of the juice falls to US$ 15.33/tonne fresh basis (US$ 69.00/tonne grain equivalent).

The basis for these calculations is that Elephant grass grown for forage produces 24 tonnes dry matter/ha/yr and contains 17 percent dry matter. The opportunity price of the Elephant grass standing in the field is the same as for a crop of cane (i.e. 100 tonnes cane stalk × US$ 13.00/tonne = US$ 1 278.00). Harvesting costs for Elephant grass are almost twice those of cane due to the lower dry matter content (17 percent versus 30 percent). Thus the final cost is US$ 77.60/tonne dry matter harvested and chopped ready for feeding.

The present Government-supported price for sorghum grain is US$ 189.00/tonne and the price of soybean meal is US$ 432.23/tonne. Indicative levels of protein are assumed to be (dry matter basis) 15 percent for a cereal-based diet and 11 percent for a cane juice diet. On this basis the comparative costs of pig rations based on grain or cane juice are likely to be those shown in Table 1. Obviously, the economic feasibility of using sugarcane juice as a substitute for cereal grain is highly dependent on integrating the pig poultry enterprises with either ruminant livestock and/or fuel production, so as to make effective use of the bagasse and cane tops.

CONCLUSIONS

The severe pressure now being put on the traditional sugarcane industry because of competition from grain-based syrups and general overproduction throughout the world calls for imaginative action by producers to develop alternative uses for this high yielding crop. An option which is profitable and at the same time satisfies the present-day food and energy needs is the integrated production of livestock products and fuel in a confinement system which facilitates recycling of nutrients through biodigesters, ponds and crops. Figure 2 illustrates the potential of this approach.

REFERENCES

Ffoulkes, D., 1980 Elloitt, R. and Preston, T.R. Feasibility of using sugarcane stalk for the production of charcoal. Tropical Animal Production, 5:125–129.

Leng, R.A. 1986 and Preston, T.R. Constraints to the efficient utilization of sugarcane and its byproducts as diets for production of large ruminants. In: FAO Expert Consultation on Sugarcane as Feed (Editors: R. Sansoucy, G. Aarts and T.R. Preston) FAO, Rome.

Mena, A. 1986 Sugarcane juice for all types of livestock. In: FAO Expert Consultation on Sugarcane as Feed (Editors: R. Sansoucy, G. Aarts and T.R. Preston) FAO, Rome.

Perez, M., 1981 Harrison, D. and Elliott, R. Rumen fermentation and kinetics on diets of sugarcane juice and molasses. Tropical Animal Production, 6:359.

Preston, T.R. 1980 A model for converting biomass (sugarcane) in animal feed and fuel. In: Animal Production Systems for the Tropics. Publication No. 8 International Foundation for Science, Stockholm.

Preston, T.R. 1986 and Leng, R.A. Matching livestock systems with available resources. International Livestock Centre for Africa, Addis Ababa, pp 331.

Figure 1: There were higher molar proportions of propionic acid and Lower proportions of butyric acid in rumen fluid of cattle fed sugarcane juice than with cattle fed molasses.

Figure 2: Model which illustrates the potential productivity from a mixed farming system.

Source: Preston and Leng, 1986.

* Assumes no use made of the residual bagasse/cane tops

** Assumes that the feeding value of the residual bagasse/tops is halfthat of Elephant grass (dry matter basis)

FRACCIONAMIENTO DE LA CAÑA DE AZUCAR PARA SU UTILIZACION COMO PIENSO Y COMO COMBUSTIBLE
por
T.R. Preston

La fuerte presión a que se ve sometida actualmente la industria tradicional del azúcar por la competencia de jarabes a base de cereales y la superproducción mundial ha estimulado la búsqueda de otros usos para la caña de azúcar.

Una opción que satisface las necesidades actuales tanto alimentarias como de energía es la producción integrada de piensos y de combustible mediante el fraccionamiento del tallo de la caña para la obtención de jugo (pienso para toda clase de animales) y los residuos prensados (combustible y/o piensos para rumiantes).

El fraccionamiento de la caña puede hacerse en las prensas o molinos tradicionales (como los utilizados para la producción de panela y de gur), que en su nivel tecnológico más bajo pueden ser accionados por animales. Se están desarrollando máquinas para la doble función de extraer el jugo y picar los residuos.

El jugo de caña se utiliza en granjas pequeñas y grandes como base de los sistemas de alimentatación de los cerdos, y se ha demostrado que técnicamente es viable su utilización como base de las dietas de las aves de corral y los rumiantes.

La caña prensada se ha utilizado como componente principal de la dieta de pequeños rumiantes y animales de tiro. Puede convertirse fácilmente en carbón vegetal y gas pobre.

El fraccionamiento de una tonelada de tallos de caña rinde aproximadamente 500 kg de jugo (100 kg de sólidos solubles) y 500 kg de forraje (200 kg de materia seca), 35 kg de carbón vegetal o equivalente de gas pobre con un valor energético de 60 l de diesel. Además, los cogollos proporcionan 250 kg adicionales de forraje (75 kg de materia seca). Los precios de oportunidad de estos productos en la explotación son tales que el valor total de la planta fraccionada puede ser igual o superior al precio de los tallos de caña vendidos para su transformación y consumo como azúcar.

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