Giant mills, vacuum pans, cristalisers and centrifugals...an imposing machinery to turn cane into juice and juice into sugar crystals.
Step 1 : crushing
In the early days of sugar production in Mauritius the words “les moulins”—the mills—were used to describe the buildings where the cane was transformed into sugar as well as the actual cylinders which did the crushing. At first these were in a vertical position; only later were they placed, as now, horizontally. In fact the word “moulin” itself is English in origin, where a variety of different manufacturing processes, but mainly for textiles, are undertaken in “the mill”. Even centuries later these enormous crushing cylinders are still called “les moulins”.
Just as one has to press a lemon to get its juice, so one has to “press” the sugar cane to get its juice—sugar. The first written records we have tell how juice was obtained from the cane by using a piston to crush it in a hollow tree trunk, much like a pestle and mortar.
Yet another ancient method, still practised here till the early years of the 20th century, was the use of a basalt cylinder, activated by hand.
Later came the vertical cylinders mentioned, above—by mechanically turning the middle of 3 cylinders, the other two were made to turn in the opposite direction. The cane was introduced to be crushed between two cylinders, the juice ran out, and the operation was repeated on the other side.
Later the cylinders were placed horizontally and those at Beau Plan were frequently modified and improved throughout the 20th century. The process of milling or crushing involves 3 or 4 cylinders—one at entry, one at the exit and the upper middle ones. All the juice cannot be extracted in a single passage, so the cane (already finely cut in pieces before coming to the cylinders) passes through a series of mills till the final fibrous residue called “bagasse” appears. In order to extract the maximum amount of juice from the bagasse it is saturated with water during this process. The juice is then weighed and analysed so that the ensuing manufacturing processes can be controlled.
The importance of bagasse
Bagasse is that fibrous part of the sugar cane that is left once all the juice that can economically be obtained has been extracted during the crushing process. Until very recently the boilers, where bagasse was burnt as fuel, reduced it completely to ash. However, over the past 30 years, sugar factories in Hawaii, Reunion and Mauritius have realized what a tremendous potential bagasse represents for the production of electrical energy. Since then the sugar industry reaps considerable financial benefit from this source. In 2002, more than 40% of the electricity produced in Mauritius comes from the sugar factories’ power plants.
The implementation of plans for the production of electrical energy from bagasse has meant that Mauritius has not only been able to diversify her sources of energy, but has also been able to modernize and centralize the sugar factories and reduce its imports of fossil fuels. What is even more important is the reduction in the emission of greenhouse gases.
Step 2 : clarification
Leaving the somewhat imposing vision of those majestic cylinders we shall now enter into the secret world of the transformation of sugar cane juice into sugar crystals. We shall see a series of industrial machines whose job is, first, to purify the juice. This is done chemically by the addition of lime, hence the term “chaulage” or “liming”—this explains the presence of so many old lime kilns in Mauritius.
The lime precipitates out the non-sugar constituants contained in the juice which will form a solid mass “les boues” (muds) which fall to the bottom of the decanter. These “boues”, after further processing are used as fertilizer for the cane fields. Nothing is wasted in the sugar cane.
Step 3 : evaporation
So that sugar can be crystallized out of the juice, it has to be concentrated first. The concentration process takes place in the evaporators—like huge great organ pipes in that cathedral of a sugar factory.
About 80% of the weight of the juice needs to be evaporated and it is this process which uses the most thermal energy in the factory. So it needs to be done as efficiently as possible—hence the need for a battery of different wooden evaporators in which the juice is gradually concentrated under the influence of steam.
Step 4 : cooking
This operation is wrongly called “cooking”—for if one really cooked the concentrated juice it would turn to caramel! Part of the whole science of sugar production lies in the use of great vacuum pans (the “vides”) to get the juice—now called “la massecuite”—to crystallize under strict vacuum temperature control. If visitors to Beau Plan so wish, they can see what it feels like to be a sugar crystal by going inside one of these huge apparatuses—but without the heat of course…
“The great vacuum pans were very clean, the copper domes of two of them were gleaming bright after being polished with ash mixed with a sort of herb, like sorrel, called “tinepatia” by the Indians. The maker’s name and the date of manufacture were artistically engraved on them. In fact, one of them is very old—one of the first ever imported here—but don’t our Creoles say “the best curry is cooked in old pots.”
Arthur Martial—In the shadow of the old mill
Step 5 : crystallization and drying process
The various machines follow one another. First the blenders like huge jaws with their upright tubes. Here the “massecuite” coming out of the vacuum containers will be cooled down to facilitate the settling down of sugar on the crystals already formed.
Then the centrifugals
Once the liquid mass has almost dried out in the blenders, the sugar crystals can be extracted in the form in which they are to be sold. This process takes place in what are called turbines or centrifuges, which are nothing other than great spin-dryers—just as clothes are dried in spin-dryers in the home. Rinsing water is evacuated from the clothes through holes in the tambour of the machine. In the sugar factory the sugar crystals stay in the tambour and it is the syrup which runs out through the holes.
This syrup is called molasses, a by-product with a high sugar content (about 30%—but very difficult to extract completely) and is used after distillation to make cane spirit. It is also exported as a base for animal feed.
The drying process
Long ago, the concentrated syrup (the mother juice) “le jus mère” was then dried in the sun, run out onto sheeting or spread out on wooden platforms. In fact the sugar leaving the centrifuges still contains 1-2% moisture which makes bad for keeping. So nowadays it is passed through a drying machine blowing hot air. At Beau Plan you’ll have to imagine the dryer, as it is no longer in place.
In the early days of sugar production in Mauritius the words “les moulins”—the mills—were used to describe the buildings where the cane was transformed into sugar as well as the actual cylinders which did the crushing. At first these were in a vertical position; only later were they placed, as now, horizontally. In fact the word “moulin” itself is English in origin, where a variety of different manufacturing processes, but mainly for textiles, are undertaken in “the mill”. Even centuries later these enormous crushing cylinders are still called “les moulins”.
Yet another ancient method, still practised here till the early years of the 20th century, was the use of a basalt cylinder, activated by hand.
Later came the vertical cylinders mentioned, above—by mechanically turning the middle of 3 cylinders, the other two were made to turn in the opposite direction. The cane was introduced to be crushed between two cylinders, the juice ran out, and the operation was repeated on the other side.
Later the cylinders were placed horizontally and those at Beau Plan were frequently modified and improved throughout the 20th century. The process of milling or crushing involves 3 or 4 cylinders—one at entry, one at the exit and the upper middle ones. All the juice cannot be extracted in a single passage, so the cane (already finely cut in pieces before coming to the cylinders) passes through a series of mills till the final fibrous residue called “bagasse” appears. In order to extract the maximum amount of juice from the bagasse it is saturated with water during this process. The juice is then weighed and analysed so that the ensuing manufacturing processes can be controlled.
The importance of bagasse
Bagasse is that fibrous part of the sugar cane that is left once all the juice that can economically be obtained has been extracted during the crushing process. Until very recently the boilers, where bagasse was burnt as fuel, reduced it completely to ash. However, over the past 30 years, sugar factories in Hawaii, Reunion and Mauritius have realized what a tremendous potential bagasse represents for the production of electrical energy. Since then the sugar industry reaps considerable financial benefit from this source. In 2002, more than 40% of the electricity produced in Mauritius comes from the sugar factories’ power plants.
The implementation of plans for the production of electrical energy from bagasse has meant that Mauritius has not only been able to diversify her sources of energy, but has also been able to modernize and centralize the sugar factories and reduce its imports of fossil fuels. What is even more important is the reduction in the emission of greenhouse gases.
Step 2 : clarification
Leaving the somewhat imposing vision of those majestic cylinders we shall now enter into the secret world of the transformation of sugar cane juice into sugar crystals. We shall see a series of industrial machines whose job is, first, to purify the juice. This is done chemically by the addition of lime, hence the term “chaulage” or “liming”—this explains the presence of so many old lime kilns in Mauritius.
The lime precipitates out the non-sugar constituants contained in the juice which will form a solid mass “les boues” (muds) which fall to the bottom of the decanter. These “boues”, after further processing are used as fertilizer for the cane fields. Nothing is wasted in the sugar cane.
Step 3 : evaporation
About 80% of the weight of the juice needs to be evaporated and it is this process which uses the most thermal energy in the factory. So it needs to be done as efficiently as possible—hence the need for a battery of different wooden evaporators in which the juice is gradually concentrated under the influence of steam.
Step 4 : cooking
This operation is wrongly called “cooking”—for if one really cooked the concentrated juice it would turn to caramel! Part of the whole science of sugar production lies in the use of great vacuum pans (the “vides”) to get the juice—now called “la massecuite”—to crystallize under strict vacuum temperature control. If visitors to Beau Plan so wish, they can see what it feels like to be a sugar crystal by going inside one of these huge apparatuses—but without the heat of course…
“The great vacuum pans were very clean, the copper domes of two of them were gleaming bright after being polished with ash mixed with a sort of herb, like sorrel, called “tinepatia” by the Indians. The maker’s name and the date of manufacture were artistically engraved on them. In fact, one of them is very old—one of the first ever imported here—but don’t our Creoles say “the best curry is cooked in old pots.”
Arthur Martial—In the shadow of the old mill
Step 5 : crystallization and drying process
The various machines follow one another. First the blenders like huge jaws with their upright tubes. Here the “massecuite” coming out of the vacuum containers will be cooled down to facilitate the settling down of sugar on the crystals already formed.
Then the centrifugals
Once the liquid mass has almost dried out in the blenders, the sugar crystals can be extracted in the form in which they are to be sold. This process takes place in what are called turbines or centrifuges, which are nothing other than great spin-dryers—just as clothes are dried in spin-dryers in the home. Rinsing water is evacuated from the clothes through holes in the tambour of the machine. In the sugar factory the sugar crystals stay in the tambour and it is the syrup which runs out through the holes.
This syrup is called molasses, a by-product with a high sugar content (about 30%—but very difficult to extract completely) and is used after distillation to make cane spirit. It is also exported as a base for animal feed.
The drying process
Long ago, the concentrated syrup (the mother juice) “le jus mère” was then dried in the sun, run out onto sheeting or spread out on wooden platforms. In fact the sugar leaving the centrifuges still contains 1-2% moisture which makes bad for keeping. So nowadays it is passed through a drying machine blowing hot air. At Beau Plan you’ll have to imagine the dryer, as it is no longer in place.