How to make corn syrup from corn starch?

Corn syrup processing equipment

The Manufacturing Process

Corn syrup is produced in processing plants known as wet corn mills. In addition to corn syrup, these mills produce many other corn products including corn oil, corn starch, dextrose, soap stock, animal feed, and several chemicals used in other industrial processes.

Separating corn starch from corn

    1 Dried, shelled corn kernels are transported to the mill in trucks, railcars, or barges. The corn is unloaded into a storage pit where it is weighed and sampled.

    2 The kernels are taken from the pit on conveyors and are passed over a set of vibrating screens or perforated metal grates to remove any sticks, husks, stones, and pieces of cob. A controlled blast of air blows away any chaff and dust, while electromagnets capture any nails, screws, or bits of metal that may have fallen in among the kernels during harvesting, shelling, or shipping.

    3 The cleaned kernels are placed in a series of large stainless steel tanks called steep tanks. Each tank holds about 168,000 lb (76,000 kg) of kernels. Warm water with a small amount of sulfur dioxide is circulated through the tanks. The sulfur dioxide reacts with the water to form a weak sulfurous acid solution. This process continues for about 20-40 hours and is used to soften the kernels and make it easier to separate the starch.

    4 The softened kernels are passed through coarse grinding mills to remove the inner portion of the kernel, called the germ, which contains most of the corn oil. Each mill has one stationary and one rotating disk. The clearance between the two disks is adjusted to tear the kernel apart without crushing the germ.

    5 The resulting pulp is transferred to a set of cyclone separators called germ separators or hydroclones. The germs, which are less dense than the other parts of the kernel, are spun out of the pulp by centrifugal force. The germs are then pumped onto a series of screens and washed several times to remove any remaining starch. The cleaned germs are heated and pressed to extract the corn oil for further processing into food products and soap stock.

    6 The remaining material from the germ separators is a slurry composed of starch, protein, and fiber. This slurry passes through another set of mills to tear the starch lose from the fiber. The fiber is then trapped on a set of washing screens and is dried to become animal feed or corn bran fiber for use in cereals.

    7 The starch and protein mixture, called mill starch, is pumped into a set of centrifugal separators that spin the mixture at high speeds. Because of a difference in specific gravity between the two materials, the heavier starch can be separated from the lighter protein, which is called the gluten. The gluten is dried and sold as animal feed.

    8 The starch is diluted with water before being washed and filtered 8-14 times to remove any remaining protein. It is then rediluted and run through a second set of centrifugal separators. The resulting starch is more than 99.5% pure. Some of this corn starch is dried and packaged for use in food products, building materials, or to produce various chemicals. The rest of it, usually the majority, is converted into corn sweeteners including corn syrup.

Converting corn starch into corn syrup

    9 Corn starch is converted into ordinary corn syrup through a process called acid hydrolysis. In this process, the wet starch is mixed with a weak solution of hydrochloric acid and is heated under pressure. The hydrochloric acid and heat break down the starch molecules and convert them into a sugar. The hydrolysis can be interrupted at different key points to produce corn syrups of varying sweetness. The longer the process is allowed to proceed, the sweeter the resulting syrup.

    10 This syrup is then filtered or otherwise clarified to remove any objectionable flavor or color. It is further refined and evaporated to reduce the amount of water.

    11 To produce a corn syrup powder, also called corn syrup solids, the liquid corn syrup is passed through a drum or spray dryer to remove 97% of the water. This produces a crystalline corn syrup powder.

Converting corn syrup into high fructose corn syrup

    12 Ordinary corn syrup contains dextrose sugar which is about three-quarters as sweet as the sucrose sugar in cane or beet sugar. In many sweetener applications this is an advantage because it does not overpower the other flavors in the food. Howev-. er, in some applications, such as soft drinks, a sweeter taste is desired. To improve the sweetness of ordinary corn syrup, it undergoes a further process called enzyme conversion. In this process, the dextrose sugars in the syrup are converted into sweeter fructose sugars by the action of an enzyme in a series of steps under carefully controlled temperatures, pressures, and acidity. This produces a high fructose corn syrup with a 42% fructose content. It is used in canned fruits and condiments.

    13 To produce corn syrups with a fructose level above 50%, syrupsthe 42% fructose syrup is passed through a series of fractionation columns, which separate and hold the fructose content. The separated portion is about 80-90% fructose and is flushed from the columns with deionized water. A portion of this is retained and sold for use in "light" foods where only a small amount of liquid sweetener is needed. The remainder is blended with other 42% fructose syrup to produce a 55% fructose syrup, which is used in soft drinks, ice cream, and frozen desserts.

    14 Powdered high fructose corn syrups can be produced by evaporating the water from the syrup and then encapsulating the powder grains to prevent them from reabsorbing moisture. Pure fructose crystals may be obtained by further processing the 80-90% fructose syrup. It is used in cake mixes and other food products where a highly concentrated, dry sweetener is desired.