Heard the one about how hard it is to milk a soy bean? Soy milk isn’t milk as we know it but it’s often used as a replacement for dairy milk. So how do they make it? HFG senior nutritionist Rose Carr investigates.
What are soy beans?
The soy bean is a species of legume (Glycine max) native to eastern Asia which has been documented as being used as a food crop since around 1700BC in north-eastern China. Because of its high oil content (at around 18-22 per cent), soy bean is actually classified as an oilseed rather than a legume. In fact, soy beans make up around 60 per cent of oilseed production in the world.
The largest producers of soy beans are the US, Brazil and Argentina. Around 260 million tonnes of soy beans are used worldwide, but only around 10 per cent is consumed directly as food for humans, such as traditional tofu and soy milk or the newer meat-like products. The rest becomes oil, animal feed, flour and other ingredients such as lecithin.
From seed to factory
There is a wide range of soy bean varieties which have different attributes, such as size and colouring, and the amounts of protein, carbohydrate and fat they contain can also vary. Different beans are used for different products such as tofu, flour or soy milk.
Soy beans grow on bushes which take about four to five months to get to one metre high. Soy beans are usually harvested when the leaves and pods have browned off and the beans themselves are a pale-yellow colour. At this stage the seeds have less moisture and have changed from a large kidney shape to a smaller, rounder shape and they are more readily separated from the pods.
Soy beans are harvested by machines which cut the plants near ground level, gathering them up and then separating the beans from their pods.
The freed soy beans are then collected into a holding tank. Generally, once they are in the factory the soy beans are cleaned, chopped and their hulls removed. The oil is often separated from the protein ‘meal’ at this point.
Making soy milk
Soy milk can be made using soy protein or it may be made from the whole beans. If using whole beans, it will be a variation of the traditional process that has been used for thousands of years.
First, the soy beans are soaked for several hours to become swollen, before being ground into a pulp with added water. This slurry is then cooked and filtered to separate out the base ‘soy milk’ from the fibre. Modern processing methods use different cooking and grinding techniques to deactivate an enzyme which produces a ‘beany’ flavour in soy milk which most western palates do not like.
To make the final soy milk that we drink, water, sugar, oil, flavours, vitamins and minerals (such as calcium) may be added. The soy milk is homogenised to ensure the fat does not separate from the rest of the milk when it sits. Most soy milk is ultra-heat-treated (UHT). The UHT process sterilises the milk and it is packaged into packs which keeps it in airless or aseptic conditions. This packaging prevents any bacterial contamination and extends the shelf life of soy milk without refrigeration or the addition of preservatives. Fresh soy milk has a short shelf life and must be stored chilled in the same way as cow’s milk.
While mature soy beans are inedible as beans, even after long boiling, edamame is the Japanese term for very young soy beans which are eaten as a snack or green vegetable. Looking much like young pea pods, these are served steamed and eaten straight from the pod by popping them out directly into your mouth. Frozen shelled edamame, a great addition to stir fries, are now available in many supermarkets.
Genetically modified soy beans
Genetically modified (GM) soy beans, such as those resistant to herbicide, became commercially available in 1996 and quickly became the main bean grown in the major producing countries. By 2010 it was estimated that GM soy beans accounted for over 80 per cent of global production. All soy beans grown in Australia, our nearest commercial growers, are GM-free. In many countries, including New Zealand and those of the European Union, most consumers prefer non-GM foods, so non-GM soy beans now command a premium price.
Most of the products on our shelves in New Zealand are GM-free, including the major brands Sanitarium and Vitasoy. Non-GM soy beans are ‘Identity Preserved’, which means the origin and qualities of the original soy beans have been identified and documented from the seed and tracked through all processing to the final soy product.
Did you know?
- Even though soy is one of the eight most prevalent food allergies, it occurs in only about 0.2 per cent of the population.
- Soy is a source of complete protein, which is unique among plant sources.