Sugar beet

Sugar beet (Beta vulgaris L.), a member of the Chenopodiaceae subfamily and the Amaranthaceae family, is a plant whose root contains a high concentration of sucrose. It 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.

The European Union, the United States, and Russia are the world's three largest sugar beet producers, [1] although only Europe and Ukraine are significant exporters of sugar from beet. Beet sugar accounts for 30% of the world's sugar production.

Culture

Sugar beet is a hardy biennial vegetable that can be grown commercially in a wide variety of temperate climates. During its first growing season, it produces a large (1–2 kg) storage root whose dry mass is 15–20% sucrose by weight. If not harvested, during its second growing season, the nutrients in this root are consumed to produce the plant's flowers and seeds. In commercial beet production, the root is harvested after the first growing season, when the root is at its maximum size.

In most temperate climates, beets are planted in the spring and harvested in the autumn. At the northern end of its range, growing seasons as short as 100 days can produce commercially viable sugarbeet crops. In warmer climates, such as in California's Imperial Valley, sugarbeets are a winter crop, being planted in the autumn and harvested in the spring. Beets are planted from a small seed; 1 kg of beet seed comprises 100,000 seeds and will plant over a hectare of ground (1 lb will plant about an acre).

Up until the latter half of the 20th century, sugarbeet production was highly labor-intensive, as weed control was managed by densely planting the crop, which then had to be manually thinned with a hoe two or even three times during the growing season. Harvesting also required many workers. Although the roots could be lifted by a plough-like device which could be pulled by a horse team, the rest of the preparation was by hand. One laborer grabbed the beets by their leaves, knocked them together to shake free loose soil, and then laid them in a row, root to one side, greens to the other. A second worker equipped with a beet hook (a short handled tool something between a billhook and a sickle) followed behind, and would lift the beet and swiftly chop the crown and leaves from the root with a single action. Working this way he would leave a row of beet that could then be forked into the back of a cart.

Today, mechanical sowing, herbicide application for weed control and mechanical harvesting has removed this reliance on workers.

Harvesting is now entirely mechanical. The sugarbeet harvester chops the leaf and crown (which is high in non-sugar impurities) from the root, lifts the root, and removes excess soil from the root in a single pass over the field. A modern harvester is typically able to cover 6 rows at the same time. The beet is left in piles at the side of the field and then conveyed into a trailer for delivery to the factory. The conveyor removes more soil -a farmer would be penalised at the factory for excess soil in his load.

If beet is to be left for later delivery, it is formed into "clamps". Straw bales are used to shield the beet from the weather. Provided the clamp is well built with the right amount of ventilation, the beet does not significantly deteriorate. Beet that is frozen and then defrosts produce complex carbohydrates that cause severe production problems in the factory. In the UK, loads may be hand examined at the factory gate before being accepted.

In the US, the fall harvest begins with the first hard frost, which arrests photosynthesis and the further growth of the root. Depending on the local climate, it may be carried out in few weeks or be prolonged throughout the winter months. The harvest and processing of the beet is referred to as "the campaign," reflecting 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).

Processing

Reception

After harvesting the beet are hauled to the factory. Delivery in the UK is by haulier or, for local farmers, by tractor and trailer. Railways and boats were once used in the UK, but no longer (some beet is still carried by rail in the Republic of Ireland).

Each load entering is weighed, and sampled before tipping onto the reception area, typically a "flat pad" of concrete, where it is moved into large heaps. The beet sample is checked for

• soil tare - the amount of non beet delivered
• crown tare - the amount of low sugar beet delivered
• sugar content ("pol") - amount of sucrose in the crop
• nitrogen content - for recommending future fertilizer use to the farmer.

From these the actual sugar content of the load is calculated and the grower's payment determined.

The beet is moved from the heaps into a central channel or gulley where it is washed towards the processing plant.

Diffusion

After reception at the processing plant the beet roots are washed, mechanically sliced into thin strips called cossettes, and passed to a machine called a diffuser to extract their sugar content into a water solution.

Diffusers are long (many metres) 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. There are three common designs of diffuser, the horizontal rotating 'RT' (from "Raffinere Tirlemontoise", the manufacturer), inclined screw 'DDS' (De Danske Sukkerfabrik)), or vertical screw "Tower". A less common design uses a moving belt of cossettes and water is pumped onto the top of the belt and pours through. In all cases the flow rates of cossettes and water are in the ratio one to two. Typically cossettes take about 90 minutes to pass through the diffuser, the water only 45 minutes. These are all countercurrent exchange methods that extract more sugar from the cossettes using less water than if they 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 red depending on the amount of oxidation which is itself dependent on diffuser design.

The used cossettes, or pulp, exits the diffuser at about 95% moisture but low sucrose content. Using screw presses, the wet pulp is then pressed down to 75% moisture. This recovers additional sucrose in the liquid pressed out of the pulp, and reduces the energy needed to dry the pulp. The pressed pulp is dried and sold as animal feed, while the liquid pressed out of the pulp is combined with the raw juice or more often introduced into the diffuser at the appropiate point in the countercurrent process.

During diffusion there is a degree of breakdown of the sucrose into invert sugars and these can undergo further breakdown into acids. These breakdown products are not only losses of sucrose but also have knock-on effects reducing the final output of processed sugar from the factory. To limit (thermophilic) bacterial action the feed water may be dosed with formaldehyde and control of the feed water pH is also practised. There have been attempts at operating diffusion under alkaline conditions but the process has proven problematic - the improved sucrose extraction in the diffuser offset by processing problems in the next stages.

Carbonatation

The raw juice contains many impurities that must be removed before crystallisation. This is accomplished via carbonatation. First, the juice is mixed with hot milk of lime (a suspension of calcium hydroxide in water). This treatment precipitates a number of impurities, including multivalent anions such as sulfate, phosphate, citrate, and oxalate, which precipitate as their calcium salts, and large organic molecules such as proteins, saponins, and pectins, which aggregate in the presence of multivalent cations. In addition, the alkaline conditions convert the simple sugars, glucose and fructose, along with the amino acid glutamine, to chemically stable carboxylic acids. Left untreated, these sugars and amines would eventually frustrate crystallization of the sucrose.

Next, carbon dioxide is bubbled through the alkaline sugar solution, precipitating the lime as calcium carbonate ( chalk). The chalk particles entrap some impurities and adsorb 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 carbon dioxide precipitates more calcium from solution; this is filtered off, leaving a cleaner golden light brown sugar solution called thin juice.

Evaporation

The thin juice, is concentrated via multiple-effect evaporation to make a thick juice, roughly 60% sucrose by weight, and 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, this 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 into the mother liquor. The syrup from the raw is also sent to a crystalliser and the very low quality sugar crystal that forms is also redissolved. The syrup separated is molasses; still containing sugar but with too many impurities to be economically processed.

There are variations on the above system, with different recycling and crystallisation paths.

Sugar beet syrup

An unrefined sugary syrup can be produced directly from sugar beet. This thick, dark syrup is produced by cooking shredded sugar beet for several hours, then pressing the resulting sugar beet mash and concentrating the juice produced until it has the consistency similar to that of honey. No other ingredients are used.

In Germany, particularly the Rhineland area, this sugar beet syrup is used as a spread for sandwiches, as well as for sweetening sauces, cakes and desserts.

History

Although beets have been grown as vegetables and for fodder since antiquity (a large root vegetable appearing in 4000-year old Egyptian temple artwork may be a beet), their use as a sugar crop is relatively recent. As early as 1590, the French botanist Olivier de Serres extracted a sweet syrup from beetroot, but the practice did not become common. The Prussian chemist Andreas Sigismund Marggraf used alcohol to extract sugar from beets (and carrots) in 1747, but his methods did not lend themselves to economical industrial-scale production. His former pupil and successor Franz Carl Achard began selectively breeding sugar beet from the White Silesian fodder beet in 1784. By the beginning of the 19th century, his beet was approximately 5–6% sucrose by weight, compared to around 20% in modern varieties. Under the patronage of Frederick William III of Prussia, he opened the world's first beet sugar factory in 1801, at Cunern in Silesia.

The development of the European beet sugar industry was encouraged by the Napoleonic Wars. In 1807 the British began a blockade of France, preventing the import of cane sugar from the Caribbean, and in 1813, Napoleon instituted a retaliatory embargo. By the end of the wars, over 300 beet sugar mills operated in France and central Europe. The first U.S. beet sugar mill opened in 1838.

Agriculture

Sugar beet is an important part of a rotating crop cycle.

Sugar beet plants are susceptible to rhizomania ("root madness") which turns the bulbous tap root into many small roots making the crop economically unprocessable. Strict controls are enforced in European countries to prevent the spread, but it is already endemic in some areas. Continual research looks for varieties with resistance as well as increased sugar yield.

Other economically important members of the Chenopodioideae subfamily:

• Beetroot
• Chard
• Mangelwurzel or Fodder Beet