Corn wet milling is the process by which we refine corn (maize) to manufacture products that are used by millions of people around the world each day. During this process, which we have outlined below, none of the corn is wasted – every part of every kernel is used in some way to produce the quality ingredients that our customers want.
Tate & Lyle uses two types of corn: dent and waxy. Dent corn is the most common, and is used to make high fructose corn syrup, food starch, ethanol and animal feed. Waxy corn is used primarily for creating stabilisers, thickeners and emulsifiers for the food industry.
First we clean the shelled corn shipments to ensure that they are free from dust and foreign bodies.
Once clean, the corn is soaked in water, called steepwater, at 50˚C for between 20 and 30 hours, during which time it doubles in size. Sulphur dioxide is added to the water to prevent excessive bacterial growth. As the corn swells and softens, the mildly acidic steepwater starts to loosen the gluten bonds with the corn, and to release the starch. The corn goes on to be milled.
The steepwater is not wasted. We concentrate it in an evaporator to capture nutrients, which are used for animal feed and fermentation.
Milling and separation
The corn is coarsely milled in the cracking mills to separate the germ from the rest of the components (including starch, fibre and gluten). Now in a form of slurry, the corn flows to the germ or ‘cyclone’ separators to separate out the corn germ.
The corn germ, which contains about 85% of the corn’s oil, is removed from the slurry and washed. It is then dried and sold for further processing to recover the oil.
Fine grinding and screening
The remaining slurry then leaves the separation step for fine grinding. After the fine grinding, which releases the starch and gluten from the fibre, the slurry flows over fixed concave screens which catch the fibre but allow the starch and gluten to pass through. The starch-gluten suspension is sent to the starch separators.
The collected fibre is dried for use in animal feed.
Separating the starch and gluten
The starch-gluten suspension passes through a centrifuge where the gluten, which is less dense than starch, is easily spun out.
The gluten is dried and used in animal feed.
The starch, which still has a small percentage of protein remaining, is washed to remove the last traces of protein and leave a 99.5% pure starch. The starch can either be dried and sold as corn starch, or it can be modified to turn into other products, such as corn sweeteners, corn syrups, dextrose and fructose
Starch to syrup conversion
To convert starch to syrup, the starch, suspended in water, is liquefied in the presence of an enzyme to convert it into a low-dextrose solution. Another enzyme is added to continue the conversion process. At any time the enzyme treatment can be halted to produce the right mixture of sugars (like dextrose or maltose) for syrups to meet different needs. In some syrups, the conversion of starch to sugars is halted at an early stage to produce low-to-medium sweetness syrups. In others, the process is allowed to proceed until the syrup is nearly all dextrose. The syrup is refined in filters, centrifuges and ion-exchange columns, and excess water is evaporated. The syrups produced are sold directly, crystallised into pure dextrose, or processed further to create high fructose corn syrup or crystalline fructose.
Dextrose is most commonly used for fermentation, although other sugars can be used. Dextrose is sent to the fermentation facilities to be converted into ethanol by traditional yeast fermentation, or into other bioproducts through either yeast or bacterial fermentation. The nutrients that remain after fermentation are used in animal feed.