Sugar (raw and refined)
Sugar is the generalised name for a class of sweet-flavored substances used as food. They are carbohydrates and as this name implies, are composed of carbon, hydrogen and oxygen. There are various types of sugar derived from different sources. Simple sugars are called monosaccharides and include glucose, fructose and galactose. The table or granulated sugar most customarily used as food is sucrose, a disaccharide. Other disaccharides include maltose and lactose.
Sugars are found in the tissues of most plants but are only present in sufficient concentrations for efficient extraction in sugarcane and sugar beet. Sugarcane is a giant grass and has been cultivated in tropical climates in the Far East since ancient times. A great expansion in its production took place in the 18th century with the setting up of sugar plantations in the West Indies and Americas. This was the first time that sugar became available to the common people who had previously had to rely on honey to sweeten foods. Sugar beet is a root crop and is cultivated in cooler climates and became a major source of sugar in the 19th century when methods for extracting the sugar became available.
Sugarcane (Saccharum spp.) is cultivated in tropical and sub-tropical regions for the sucrose that is found in its stems. It requires a frost-free climate with sufficient rainfall during the growing season to make full use of the plant’s great growth potential. The crop is harvested mechanically or by hand, chopped into lengths and conveyed rapidly to the processing plant. Here it is either milled and the juice extracted with water or the sugar is extracted by diffusion. The juice is then clarified with lime and heated to kill enzymes. The resulting thin syrup is then concentrated in a series of evaporators and then further water is removed by evaporation in vacuum containers. The resulting supersaturated solution is seeded with sugar crystals and the sugar crystallizes out and is separated from the fluid and dried. Molasses is a by-product of the process and the fibre from the stems, known as bagasse, is burned to provide energy for the boiling of the syrup. The crystals of raw sugar have a sticky brown coating and can either be used as they are or can be bleached by sulphur dioxide or treated in a carbonation process to produce a whiter product.
Sugar beet (Beta vulgaris) is a tuberous root which contains a high proportion of sucrose. It is cultivated in temperate regions with adequate rainfall and requires a fertile soil. The crop is harvested mechanically in the autumn and the crown of leaves and excess soil removed. The roots do not deteriorate rapidly and may be left in a clamp in the field for some weeks before being transported to the processing plant. Here the crop is washed and sliced and the sugar extracted by diffusion. The raw juice is then treated with lime and carbonated in a number of stages in order to purify it. Water is evaporated by boiling the syrup under a vacuum. The syrup is then cooled and seeded with sugar crystals. The white sugar which crystallizes out can be separated in a centrifuge and dried. It requires no further refining.
Granulated suguars are used at the table to sprinkle on foods and to sweeten hot drinks and in home baking to add sweetness and texture to cooked products. They are also used as a preservative to prevent micro-organisms growing and perishable food from spoiling as in jams, marmalades and candied fruits.
Milled sugars are ground to a fine powder. They are used as icing sugar, for dusting foods and in baking and confectionery.
Screened sugars are crystalline products separated according to the size of the grains. They are used for decorative table sugars, for blending in dry mixes and in baking and confectionery.
Brown sugars are granulated sugars with the grains coated in molasses to produce a light, dark or demerara sugar. They are used in baked goods, confectionery and toffees.
Sugar cubes are white or brown granulated sugars pressed together in block shape. They are used to sweeten drinks.
Liquid sugars are strong syrups consisting of 67% granulated sugar dissolved in water. They are used in the food processing of a wide range of products including beverages, ice cream and jams.
Invert sugars and syrups are blended to manufacturers specifications and are used in breads, cakes and beverages for adjusting sweetness, aiding moisture retention and avoiding crystallization of sugars.
Syrups and treacles
Syrups and treacles are dissolved invert sugars heated to develop the characteristic flavours. Treacles have added molasses. They are used in a range of baked goods and confectionery including toffees and licorice.
Low calorie sugars and sweeteners
Low calorie sugars and sweeteners are often made of maltodextrin with added sweeteners. Maltodextrin is an easily digestible synthetic polysaccharide consisting of short chains of glucose molecules and is made by the partial hydrolysis of starch. The added sweeteners are often aspartame, saccharin, stevia or sucralose.
Polyols are sugar alcohols and are used in chewing gums where a sweet flavor is required that lasts for a prolonged time in the mouth.
Raw sugar is used not only to produce consumer sugar but also without further industrial processing in breweries, the industry and as a feedstuff.
Shipment / storage / usage
Special care should be exercised in ascribing the cause of damage to this commodity, particularly in the case of alleged water or moisture damage. If not dry to the point at which it is in equilibrium with the relative humidity of the atmosphere, sugar may continue to lose moisture in storage, stowage, etc., dry and tend to cake. Similarly, if the sugar is too dry it will absorb moisture from the atmosphere until it reaches equilibrium and if atmospheric conditions change and it dries again it will tend to cake. If the sugar is excessively dried it may suffer in lustre and from dust formation. Sugar dried to equilibrium by the manufacturer will, if exposed to atmosphere of high humidity, i.e. in damp localities or during the voyage, inevitably re-absorb moisture to the higher level of the surrounding atmosphere. The absorption or loss of moisture after leaving the manufacturers’ premises will not be apparent until there is a further change in the relative humidity of the atmosphere. For instance, sugar which has been packed in a relative humidity of say 65%, may well await shipment in a relative humidity of 85%, and will come to equilibrium with the atmosphere and, to all intents and purposes, the sugar will appear to be unaffected. After loading into the vessel, however, the relative humidity of the atmosphere may fall to 65%, and under these circumstances the sugar will lose moisture. During this process it will dry and cake.
A relative humidity of between 80% and 85% is generally regarded as a critical level for sugar. Above this humidity sugar always tends to gain moisture very rapidly, while below it, it remains relatively unaffected. Even although the sugar gains moisture rapidly above 80% to 85%. R.H., the first effect of the gain is merely to increase the moisture content and does not produce caking. A subsequent fall in humidity will, however, tend to dry the sugar out and will inevitably produce caking and lumpiness throughout the whole as the dissolved sugar on the outside of the crystals adheres to its neighbour. When damaged by fresh or salt water, sugar should not be considered a total loss, as the quantity remaining after draining should show little loss in polarisation; sugar remaining after draining should show a greater degree of polarisation than when wet. Cases have been known where sugar which had been totally submerged showed only a small loss in polarisation. If local facilities are available for re-refining, it is in the best interests of all concerned to have the damaged sugar forwarded immediately to the refinery for reprocessing. If the damaged sugar is landed at a port of distress, where no immediate facilities for reconditioning the sugar are available, it is sometimes advisable to have the sugar forwarded promptly to its destination. Damaged sugar may commence to deteriorate within a short time of the accident. The possibility of further damage arising due to fermentation and other factors during transit should also receive attention. Damaged sugar which has been rendered unfit for normal consumption may sometimes be used for animal feed, for alcohol production or in other manufacturing processes. A market for burned sugar may be found for brewing purposes.
When examining sugar the following points should be borne in mind:
a) Surveyors should refrain from expressing an opinion as to the cause of damage unless there is clear evidence to support such opinion, e.g. rain during discharge, etc.
b) Where samples are tested for the presence of sea water and the reaction is negative, the analyst should state this fact; where the reaction is positive, the analyst should specify the salts found. It is desirable that a sound sample, both of wrapping and contents, should be similarly tested. It is sometimes not appreciated that raw and refined sugars – both cane and beet – react with silver nitrate to show traces of salt. The slat comes originally from the soil and may be many miles from the sea.
c) It is essential that the condition of the goods should be described in fullest detail and all possible inquiries made in an endeavour to establish the cause of any alleged damage. As most white sugar is now transported in polythene lined sacks, even if the outside looks wet or mouldy the goods are marketable. The poly liner was designed many years ago to survive landing through the surf ports of West Africa.
d) If foreign matter is found the analyst should state whether it is of an injurious character or otherwise.
e) Sugar kept in damp storage is liable to inversion due to mould growth on the bags.
f) Cane Sugar (unrefined) – Also known as raw sugar. At the end of each crop season quite large quantities of sweated sugar, due to lying in storage, are found. This might readily be mistaken for damage in transit.
Additional information on sugar
Sugar is a moisture-sensitive cargo, it should not be loaded into the same container with copra because the copra beetle will affect the sugar. Do not stow with odor sensitive cargoes such as coffee and tea, also sugar and cement must not be stowed together since mixing deteriorates both products. Sugar becomes like treacle when wet and corrodes the container steelwork, therefore container must be scrupulously clean and dry. As protection for the container an innerliner must be fitted.
Once loaded, the mass is immobile but its volume may go down by 5%, because of the vibrations of the ship. Unrefined sugar will rarely harden.
Raw sugar absorbs moisture from the outside air and experience has shown that sugar should not be ventilated during transit. A drawback is that alcohol vapors produced will not be carried off and therefore containers should only be opened in a ventilated space and sufficient time allowed to gas-free. Care should be taken with hold-lighting and open fire in connection with the alcoholic vapors. During stuffing the risk of explosion is eminently present.
The carriage of unrefined sugar
Sugar itself has no effect on the container’s structure, but when dissolved in water, acids will be formed which cause corrosion. Before commencing to stuff sugar, following measures must be taken:
- Containers to be loaded must be very well cleaned.
- Floor ceiling, openings etc., be stopped.
- An innerliner must be fitted for receiving the cargo
- After the sugar has been discharged, the area must be properly spray cleaned. It is recommended however, first to broomclean the floor as good as possible; with some kinds of sugar this will give excellent results.
The carriage of refined (crystal) sugar
Unlike semi-refined or raw sugar, refined sugar is always carried in bags. In the past, jute outer bags were widely used with a polyethylene film inner bag. Nowadays the outer bags are often made from woven polypropylene. The purpose of the plastic inner bag is to keep out moisture but because the outer and inner bags are often stitched together, the seal is not always effective.
Refined sugar is normally a dry, free-flowing commodity with very low moisture content. If the sugar is found on delivery not to be free flowing, it is important to establish whether this is due to:
1) Pressure compacting
Pressure compacting usually occurs as a result of static pressure exerted by the weight of the sugar itself, especially when bags are stacked high. This condition can readily be corrected when the bags are handled and moved around. However, stickiness and caking of refined sugar are both the result of too high a moisture content and possibly to some extent, the temperature of the cargo at the time of bagging.
Stickiness, resulting in poor flow characteristics, occurs as a result of high moisture content, either initially or after packing.
Caking may occur when over moist sugar dries out.
If the product comes into contact with extraneous moisture such as cargo sweat, this may lead to limited, superficial stickiness and the subsequent caking of the sugar at the mouth of the bags. This may also occur where bags have been damaged by stevedores’ hooks. Should more extensive stickiness and caking occur, this is caused by excessive moisture at the time of packing, particularly if the caking is found at the centre of the bag, spreading out towards the periphery, with stickiness at the outer parts. This condition may be further affected if, at the time of packing, the temperature of the sugar is high, relative to the ambient temperature. Thus, it is vital that correct practices are observed during the manufacturing process.
It is of crucial importance that, immediately after production, the amounts of so called ‘free water’ and ‘bound water’ are at satisfactory low levels. After processing, sugar is normally left in storage for a relatively short period, with appropriate ventilation, in order to ‘condition’ or ‘mature’ the product. The aim of this is to ensure that when the sugar is bagged, its moisture content is at an acceptable low level. If it is not, comparatively hard caking and possibly some stickiness can be expected to occur during subsequent storage and transport. When sugar is bagged with a low moisture content (0,02% or less) then there is no risk of stickiness or caking being caused by moisture migration. At a water content > 0.05%, sugar quality may be impaired by inversion of the sucrose, i.e. dissolution into the monosaccharides, glucose and fructose. This sugar inversion may be brought about by the enzyme invertase in microflora (primarily by yeasts and molds) at a relative humidity > 75%, a process which occurs particularly rapidly at an elevated moisture content of the sugar. Only matured sugar with a water content < 0.05%, or < 0.03% for longer voyages, may thus be loaded. Relative humidities > 70% result in syrup formation, tackiness and mold and yeast growth. At below 50%, the sugar may harden, cake and lose its flowability. Some sale contracts stipulate a moisture content of ‘0,1% maximum’ but it should not be assumed that such levels are acceptable if caking is to be avoided. Stickiness and caking do not affect the chemical nature of the sugar but may not be acceptable depending upon its intended use. The release of water vapor from excessively moist sugar causes recrystallization and consequently agglomeration (sticking together). The hygroscopicity of sugar is determined by the film of syrup covering the sugar crystal. Optimum relative humidity is 55 – 65%. Up to 60%, the water content of the sugar rises only insignificantly to approx. 0.04%. At relative humidities of 60 – 80%, water content rises markedly (> 0.08%), while at 85% the flow moisture point of sugar is reached, at which a saturated solution forms on the surface of the crystal due to absorption of water vapor. As a result, the sugar loses its flowability, which is an important property especially for bulk cargo transport.
Because most marine reference books are silent on the carriage of refined sugar, it is often assumed that it is a relatively simple product to handle, subject only to the most general stowage and ventilation recommendations. Tight block stowage without height limitation, is the customary and acceptable method, the height of the stow being limited only by the height of the cargo compartments. Cargo battens are not necessary as it is generally accepted that a separation of paper or cardboard sheets or of polyethylene or polypropylene cloth between the ship’s structure and the bags, is sufficient. Ventilation of refined sugar is not necessary under any circumstances. The purpose of cargo ventilation is to prevent or restrict the formation of condensation or moisture on the ship’s internal structure. However, such condensation originates from within the cargo and will occur only when the cargo itself is moist or damp. Because refined sugar has a low moisture content and is enclosed in plastic film, there is no risk of sweat. Under certain circumstances, ventilation may even be detrimental, for example when holds loaded with cold cargo are ventilated with warmer air, this can lead to the formation of sweat.
Sugar has a low thermal conductivity which means that during the voyage, it tends to remain at the same temperature at which it was loaded, at least in the interior of the stow. If the sugar is loaded cold and later discharged in a relatively hot area, there is a risk of condensation forming during the discharge, on any bags having a temperature lower than the dew point of outside air. In such cases rapid discharge is necessary in order to avoid any adverse consequences.
- The ship’s holds before loading, should be clean, dry and free from any noticeable smell.
- Bags should be loaded only if outwardly dry with no apparent lumpiness of the contents
- No bags to be loaded during any form of precipitation including rain or snow
- Cargo battens are not essential: where no battens are fitted, measures should be taken to prevent damage from any protruding cargo batten hooks or fittings.
- A separation of polyethylene or polypropylene cloth or paper sheeting between the ship’s structure and the bags is sufficient.
- Tight block-stowage is the customary and acceptable method of stowage.
- If additional cargo is to be carried in the same hold as refined sugar, then this should be ‘dry’ cargo.
- The holds should not be ventilated: all ventilators and other openings should be sealed.
- The rapid discharge of any bags which may have been loaded at substantially lower temperatures than at the discharge port, is necessary, in order to prevent or restrict unwanted condensation on the bags during discharge.
Raw sugar is particularly hygroscopic due to its high ash content and readily releases water vapor and must thus be protected from all forms of moisture (seawater, rain, condensation water). At relative humidities below the flow moisture point, raw sugar responds little to the water vapor content of the ambient air and the water content remains close to 0% (0.25 – 1.1%). Once the flow moisture point is reached at a relative humidity of 80%, the raw sugar readily absorbs water vapor, resulting in an abrupt rise in the sorption isotherm, and the sugar crystals deliquesce.
This marked hygroscopicity of raw sugar is attributable to the film of (strongly hygroscopic) molasses remaining on the sugar crystals. Moisture reduces the concentration of the sugar. The change in sugar concentration is determined by polarization measurement (optical measurement method).
Relative humidities > 70% result in agglomeration (sticking together), syrup formation, tackiness, loss of flowability and mold and yeast growth, which cause fermentation. At below 50%, the raw sugar may harden, cake and lose its flowability. Monolithic layers may arise which cannot be unloaded without prior loosening. Moisture and agglomeration damage may be avoided by incorporating additives. Subject to compliance with the appropriate temperature and moisture/humidity conditions, the maximum duration of storage is not a limiting factor as regards transport.
High relative humidities or fog have no negative impact upon unloading operations because the raw sugar is further processed into white sugar. On the other hand, losses do arise due to caking if the relative humidity drops. Hardening has, for example, been observed to occur even during unloading at low temperatures and low humidities. In dry weather at a low relative humidity, raw sugar has been found to be so hard that problems arose during unloading, while no such problems arose in humid, hot weather. Raw sugar has also been found to be unusually hard due to low humidity in frosty conditions.
Favorable travel temperature range: no lower limit – 25°C. Agglomeration (sticking together) is promoted by relatively high temperatures (> 25°C) due to release of water vapor. Sugar should not be stowed near heat sources. Temperature variations should, as far as possible, be avoided as the resultant release of water vapor and recrystallization may result in caking. Raw sugar with a loading temperature of above 48°C should not be accepted as it may cake on cooling.
Raw sugar requires particular humidity/moisture and possibly ventilation conditions. As bagged raw sugar is protected from water vapor exchange by a plastic lining, it does not normally need to be ventilated. However, if it is transported as bulk cargo, note should be taken of the behavior of a cargo block in the event of temperature changes.:
Transport from temperate latitudes to the tropics = travel from cold to hot: the cargo block is heated from the outside, resulting in water vapor transport from the outside to the cold core, which causes caking of the outer layers while the inner layers display wetting phenomena (syrup formation).
Transport from the tropics to temperate latitudes = travel from hot to cold: if the cargo block cools down from the outside, resulting in water vapor transport from the warm core to the outside, wetness and mold may occur there while inside the release of water vapor by the warm core results in caking phenomena (loss of flowability).
On short voyages, ventilation need not be provided or, if provided, must not be too intense, so that the initial relative humidity and temperature conditions are maintained for as long as possible. On longer voyages (e.g. Cuba to Europe), return air ventilation may be provided to prevent mold growth on the bags, but the removal of moisture may result in caking.
- Self-heating / Spontaneous combustion
- Mechanical influences
- Shrinkage / Shortage
- Insect infestation / Diseases