sugar beet

Other Definitions
sugar beet (dict)

Sugar beet Beta vulgaris L., one of the Chenopodiaceae of the Amaranthaceae family, is a plant that contains a very high concentration of sucrose, and is grown commercially for sugar. The sugar beet is directly related to the beetroot, chard and fodder beet all descended by cultivation from the Sea Beet Sugar beets are grown mainly in Europe, the United States, and China http://www.fao.org/es/ess/top/commodity.jsp?lang=EN&commodity=157&CommodityList=157&year=2003&yearLyst=2003. Beet sugar accounts for 30% of the world's sugar production.

Sugar extraction

Harvest

The beets are harvested in the autumn. Depending on climate and geography the harvesting may take a few weeks or carry on into the winter months. The harvest and processing of the beet is referred to as "the campaign" relecting the organization required to deliver crop at a steady rate to processing factories that run 24 hours a day for the duration of the harvest and processing (for the UK the campaign lasts approx 5 months). Harvesting is almost entirely mechanical, removing the leaf and crown (which is high in non sugar impurities and lifting the root in one operation. Excess soil is removed before transporting to the processing plant.

Diffusion

After reception at the processing plant the beet roots are washed, sliced into chips known as cossettes, and passed to a machine called a diffuser to extract their sugar content into a water solution. Diffusers are long (many metres), horizontal ('RT'), sloping ('DDS'), or vertical ('Tower') vessels in which the beet slices go in one direction while hot water goes in the opposite direction. The movement may either be by a rotating screw or the whole unit rotates and the water and cossettes move through internal chambers. A less common process uses a moving belt of cossettes and water is pumped onto the top of the belt and pours through. Typically cossettes take about 90 minutes to pass through the diffuser, the water only half that. These are all counter-current flow methods, and extract more sugar from the cossettes for less water than if they were merely sat in a hot water tank. The liquid exiting the diffuser is called raw juice. The colour of raw juice varies from black to a dark black-red depending on the amount of oxidation which is itself dependant on diffuser design. Once the cossettes have passed through the diffuser they still contain a substantial amount of sugar in liquid, so they are pressed in a screw press to extract further liquid (which is added to the raw juice) and also reduces the amount of drying of this material. The remaining beet pulp is turned into animal feed, and the beet juice is further processed.

Carbonatation

The next stage in processing is carbonatation. The sugar juice contains many impurities that must be removed before crystallisation. To do so, the raw juice is mixed with milk of lime and carbon dioxide rich gas in carbonatation tanks. The alkaline lime precipitates impurities such as proteins and the carbon dioxide bubbling through the mixture forms calcium carbonate (chalk) particles. These particles form around the impurities and absorb some others. A recycling process builds up the size of chalk particles, and a natural flocculation occurs where the heavy particles settle out in tanks (clarifiers). A final addition of more CO2 gas precipitates more calcium from solution and this is filtered off, leaving a cleaner golden light brown sugar solution called thin juice.

Evaporation

To concentrate the juice, it is boiled under reduced pressure in a series of evaporators where about half the water is removed, forming a thick juice similar in appearance to pancake syrup. Thick juice can be stored in tanks for later processing reducing load on the crystallization plant.

Crystallization

The thick juice is fed to the crystallisers, with recycled sugar dissolved into it it is called "mother liquor". This is concentrated further by boiling under vacuum in large vessels and seeded with fine sugar crystals. These crystals grow as sugar in the syrup forms around them. The resulting sugar crystal and syrup mix is called a massecuite (French. 'cooked mass'). The massecuite is passed to a centrifuge where the liquid is removed from the sugar crystals. Remaining syrup is rinsed off and the crystals dried in a granulator using hot air. The remaining syrup called is fed to another crystalliser from which a second batch of sugar is produced. This sugar ("raw")is of lower quality and is re-dissolved inot the mother liquor. The syrup from the raw is also sent to a crystalliser and the very low quality sugar crystal fomred is also redissolved. The syrup separated is molasses; still containing in sugar but with too many impurities to be economically processed. There are variations on the above system, with different recyling and crystallisation paths.

Discovery

Beets (and carrots) were identified as potential sources of sugar by the Prussian chemist Andreas Sigismund Marggraf in 1747, but he thought that commercial extraction would be uneconomic. His former pupil and successor Franz Carl Achard began selectively breeding sugar beet from the White Silesian fodder beet in 1784. Achard was the first to start producing beet sugar commercially in 1802, following the opening of the world's first beet sugar factory in Kunern, Germany in 1801. At the time his beet was approximately 5% to 6% sugar, compared to around 20% in modern varieties. The development spread rapidly in France and Germany, encouraged by the imposition in 1807 of a blockade by the English in the Napoleonic Wars, which prevented the import of cane sugar.

Use

Sugar beet is an important part of a rotating crop cycle. Sugar beet plants are susceptible to rhizomania which turns the bulbous tap root into many small roots making the crop economically unprocessable. Continual research looks for varieties with resistance as well as increased sugar yield. Other economically important members of the Chenopodioideae subfamily: