Understanding how soy lecithin is made is easier if you know a few basic terms that aren’t used very often outside the soy lecithin industries.
First, it’s important to understand that lecithin, on a chemical level, is really a mixture of several fatty compounds, primarily choline and cephalin. Both choline and cephalin are useful in making emulsions of oils and water, or oils, water, and other ingredients, but choline is better for emulsifying a smaller amount of oil in a larger amount of water, and cephalin (also known as alpha-phosphatidylethanolamine) is better for emulsifying a smaller amount of water in a larger amount of oil. Cephalin also has a tendency to clump when it’s added to hard water. “Native” soy lecithin contains both choline and cephalin, but there are several ways to reduce the amount of cephalin in the finished product.
It’s also important to understand the difference between hexane and hexanes. (Both terms are singular.) “Hexanes” is a mixture of the solvent hexane with some closely related chemicals, primarily 2-methylhexane, 3-methylhexane, and small concentrations of non-isomeric C5, C6, and C7 cycloalkanes. Hexanes are less expensive than pure hexane, and suitable for use in this process because removing the soy lecithin mixture does not require a specific chemical.
With that terminology explained, we can now discuss the making of soy lecithin—from soybeans.
The Manufacturing Process
Soy lecithin begins as whole soybeans.
The soybeans are dried at the time farmers deliver them to grain elevators. When the soy lecithin manufacturer needs beans for processing, they are sent through rollers to be hulled. At this point, they may be dried some more, or less often, hydrated to reach the right percentage of moisture for later processing. The soybeans then go into an oven to reach a temperature of 60 and 88° C (140–190 °F). They tumble down a conveyor belt so they can be crushed into whole soybean flakes.
The flakes are allowed to cool slightly, at least to 69 °C (156 °F), and then mixed with hexanes to extract the lecithin. The mixture of hexanes and soy lecithins is filtered and the hexane is boiled off to leave the lecithins.
Soy lecithin can also be made without hexanes.
This process starts with soybean oil. The soybean oil is slightly diluted with water (2 to 3 percent the volume of the oil) and heated to 50 to 70° C (122–158 °F). The lecithins are then hydrated to form a sludge.
In this process, the next stage is desliming. The lecithins are kept at 50 to 70° C (122–158 °F) as they are placed in a centrifuge. The deslimed soybean oil contains up to 0.5 percent lecithins and the lecithin sludge beneath it contains 40 to 50 percent water.
After the lecithin sludge is created, the water in it must be evaporated off to keep it fluid and to prevent spoilage. The manufacturer can use horizontal film evaporators for fast processing or vertical evaporators when it is necessary to remove a solvent.
Once the lecithin is dried, it must be cooled to between 20 and 30° C (68 and 86° F) to prevent discoloration. After drying, soy lecithin can be kept at room temperature for months without deterioration of quality.
Soybean lecithin is naturally reddish-brown in color. They can be treated with hydrogen peroxide in the desliming stage to make it light brown or tan. A second treatment with hydrogen peroxide may be used to make the final product especially light, usually for applications in the food industry. Calcium may also be added to soy lecithin to make it more viscous and easier to use in extrusion processes. Almost all soybean lecithin contains a significant percentage of soybean oil in its final form, which means that it is typically not advisable for those with soy allergies to consume it.