Sugar refining transforms raw sugar cane or sugar beets into pure sucrose, which is processed into various physical states to meet the specific requirements of the sugar-using industries. A series of treatments purify raw sugar, turning it into a water-clear syrup from which sugars of specified particle sizes are obtained. Commercial sugars are generally differentiated into two broad categories: granulated and powdered sugars.
Granulated sugars range from coating sugar, an extremely fine-grained sugar used principally for coating confectioneries, through such grades as bakers special, fruit granulated, extra fine, fine, medium fine, medium, standard and coarse granulated sugar, with each type consisting of ever larger grains in ascending order, and often finding specific applications that require certain particle size characteristics. Fine granulated styles, for example, suit fillings where sugar is not completely dissolved and a larger particle size would produce gritty results.
In all of these sugar types, the variations in grain size are achieved by a judicious control of the crystallization process and by passage of the crystals over sieves for separation according to size. Bakers special, for example, is a medium-sized particle (US 50 to 140 mesh), a little finer than standard granulated or common table sugar. Fruit granulated sugar is slightly finer than extra fine, with a grain size distribution between US 40 and 100 mesh.
Two other forms of granulated sugar warrant discussion: turbinado and sanding sugars. Turbinado sugar, which is sometimes sold at retail under the names “raw sugar” or “natural sugar,” has undergone some refining to remove impurities and most of the molasses present in true raw sugar. Bakers use sanding sugar to sprinkle on the tops of cookies, pies and other sweet baked foods where particles of sugar on the surface add to the desired appearance of the finished baked product.
In a class by itself, evaporated cane juice is dry crystalline sugar produced from sugar cane, but it does not undergo the same degree of processing as granulated sugar and thus retains more of the plant’s native nutrients, riboflavin being the most significant. Other names for this sweetener include dried cane juice, crystallized cane juice and milled cane sugar. In Europe, it is termed “unrefined” sugar. In milled form, it consists of small-grained crystals, gold in color with a mild molasses flavor. Coarser crystals and a noticeable molasses flavor characterize the demerara form of evaporated cane juice, while the muscovado style offers fine crystals and a pronounced molasses flavor. Producers of natural foods tend to use evaporated cane juice, replacing highly refined sugars.
Finally, raspadura (also called rapadura and panela) is a traditional Latin American sugar produced by boiling sugar cane to remove its water content.
Powdered sugars are made by grinding coarse granulated sugar in special mills and screening through fine bolting cloths. Finely powdered sugars tend to cake readily on storage, a condition alleviated by the addition of 3% re-dried corn starch or 1% tricalcium phosphate as anticaking agents during grinding. Powdered sugars are also available in various degrees of fineness (indicated by a series of Xs). They range from fondant sugar, an extremely fine-grained product nearly all of which will pass through a 325-mesh screen with openings of 0.0017 in., through ultrafine (confectioners 10X), very fine (6X), fine (4X), medium and coarse. There is a significant difference in the coarseness of 6X and 10X sugars. At the same time, however, a great deal more energy is required to reduce sugar to 10X than to 6X size and the output of a pulverizer is correspondingly reduced by 50% when production is changed from 6X to 10X. Average particle size 6X sugar should be small enough to permit at least 90% to pass through a 200-mesh screen. At least the same proportion of 10X sugar should pass through a 325-mesh screen.
The various designations applied to granulated sugars are mainly descriptive and do not specify generally accepted particle size standards. This applies to powdered sugars as well. Hence, two sugars of different origin but having the same number of Xs assigned to them are not necessarily identical in their degree of fineness.
Powdered sugars are used primarily in icings and fillings but also as dusting sugars. While 6X sugar yields very satisfactory icings of both the flat and cream types, smoother and more tender icings that approach the character of fondants can be made with 10X sugar (Broeg 1976).
Among other types of sugar available commercially in dry form is transformed sugar, also called microcrystalline sugar. The production process was described by Chen and Awad (1993). An evaporator raises the concentration of the sugar syrup to 91 to 97% solids, which is put through a flash-drying process. This method imparts a very irregular particle structure. As a result, the product is highly aerated, crumbles readily, dissolves almost instantly and is for these reasons particularly suited for creaming with shortening in cake making. The majority of the crystals are 5 to 10 microns in size. Even at 2% moisture, the dry sugar remains free-flowing after storage. In Portugal, transformed sugar is called areado.
Cocrystallized sugar results spontaneously from rapid agitation of a supersaturated sugar solution, resulting in agglomerated microscopic crystals. They are sponge-like in appearance, with considerable void space and large surface area. Other ingredients such as flavors can be added to the solution and will be taken up in the interstitial space between crystals (Chen et al. 1982).
The so-called “soft” sugars, also known as brown sugars, contain varying amounts of the mother liquor occluded to the sugar crystals, thus giving them a moisture content of 2 to 4%. They range in color from nearly pure white to dark brown and are assigned color grades ranging from No. 1 for the lightest product to No. 15 for one with the color of roasted coffee. In practice, only three grades, namely light, medium and dark, are usually marketed. They possess a pleasing caramel-type flavor, and the dark grades find their major uses in products such as rye bread, gingerbread, dark cakes, cookies, etc. When stored under relatively dry atmospheric conditions, they tend to fuse into solid blocks that can cause major difficulties in their handling.
Granulated and powdered sucrose should be stored under dry conditions of less than 60% relative humidity (RH), and fluctuations of humidity should be avoided. Brown sugars, on the other hand, are best held at 65 to 70% RH to ensure their moisture and softness retention (Matz 1972). Sugar that is exposed to high humidity conditions will absorb moisture on the surface crystals to form a concentrated syrup that fuses the crystals together. When moisture evaporates later, the fused crystals harden into a crust, destroying the homogeneous granulation of the sugar.
Broeg, C.B. 1976. Sucrose. Proc. Am. Soc. Bakery Engrs. 52: 170.
Chen, A.C.C, and Awad, A. 1993. Specialty sugars. In: Cane Sugar Handbook. J.C.P. Chen, A.C.C. Chou and G.P. Meade, eds. John Wiley & Sons: New York, NY.
Chen, A.C.C., Lange Jr., C.E., Graham, C.P., and Rizzuto, A.B. 1982. Crystallized, readily water-dispersible sugar product. US Patent No. 4,338,350. And: Crystallized, readily water-dispersible sugar product containing heat-sensitive, acidic or high invert sugar substances. US Patent No. 4,362,757.
Matz, S.A. 1972. Bakery Technology and Engineering, 2nd ed. Avi Publishing Co.: Westport, CT.
More on this topic can be found in “Baking Science & Technology, 4th ed., Vol. I,” Page 178, by E.J. Pyler and L.A. Gorton. Details are in our store.