Artisanal production of maltose from cassava starch

One simple sugar is glucose which is found in most living organisms. Glucose exists in many different forms and is by far the most common carbohydrate.

In most developed countries, food manufacturers have access to a wide range of sweeteners. These include sweeteners that provide energy, such as sucrose made from cane sugar and various syrups made from starch. Low calorie sweeteners, including various naturally occurring proteins and synthetic substances such as saccharin are also available and are widely used in dietetic foods. In developing countries, food manufacturers hare limited access to sweeteners other than cane sugar. Starch based sweeteners usually have to be imported.

The main source of energy in the human diet is a group of substances called carbohydrates, made from carbon, hydrogen and oxygen and having the general formula C_x(H₂O)_y. Some carbohydrates, including the commonest starch, have little or no sweetness. Others taste sweet, and these are termed sugars. One simple sugar is glucose which is found in most living organisms. Glucose exists in many different forms for example combined with a large number of other glucose molecules as a glucose polymer in cellulose and starch. In sucrose it is combined with another simple sugar, fructose. In one form or another, free or combined, glucose is by far the most common carbohydrate.

Long chain carbohydrates can be broken down into fragments, by a process known as hydrolysis. Cellulose is very difficult to hydrolyse because of the way that the glucose units are joined together, but starch can be broken down quite easily, either using hot acid or by using naturally occurring substances called enzymes. Enzymes that hydrolyse starch are called amylases and are found in many living organisms including bacteria, fungi, plants and animals. By hydrolysing starch, a range of sugars can be obtained that contain both glucose and its polymers (chains of glucose units of various lengths). The sweetness of a glucose polymer depends on how many glucose molecules can be made from it - the smaller the number, the sweeter the polymer will be. Rating sucrose at 100 on a scale of sweetness, glucose rates between 60 and 70, while maltose (with two glucose molecules) rates about 40.

For many years, people in Vietnam have been making a sweetener from starch using a small-scale artisanal process. This sweetener is called maltose, because it contains over 50 per cent of that sugar and it is used in making many different food products. The process uses the amylases present in cereal seedlings to break down the starch. Only very simple equipment is needed. A new FAO manual Sweetness From Starch'* gives a detailed description of the equipment that is needed and the process for making maltose syrup.

AN OUTLINE OF THE MALTOSE PROCESS

Moist starch from a settling basin in a typical traditional starch factory is the preferred raw material. It does not have to be completely fresh, but it should be clean and not badly fermented. Traditionally only cassava starch has been used, but the source of the starch is probably not important. Amylase is obtained from either rice or maize seedlings - most varieties of either grain are satisfactory, although some are said to be better than others. The seeds are germinated, allowed to sprout and are ready for use after about 10 days -when the shoots are 10 cm long and the main root about 6 cm long. Shortly before the amylase is needed, the whole plant (shoot, seed and roots) is chopped or crushed.

Heating and evaporation are carried out in an open pan over a furnace, in much the same way as traditional sugars such as gur or panela are made. Temperatures at certain stages of the process are quite critical - if too hot, the amylase may be inactivated and if too cool, the amylase activity will be reduced. Obviously temperature fluctuations are likely in small batches and for this reason batches less than half the size indicated below are not recommended.

A TYPICAL OPERATION ROUTINELY USED IN VIETNAM

Mix together 40 kg of moist starch with 10 litres of warm (60°C) water, to form a slurry, making sure no lumps remain. Mix 4 kg of freshly crushed seedlings into the slurry. Make a second batch in exactly the same way. Boil 120 litres of water - if appropriate, the water may contain sugar washed out of seedlings during an earlier operation. Stir the boiling water into one of the hatches of slurry. The starch will gelatinise, but the amylase in the crushed seedlings will thin the paste and within about a minute it should be runny and barely thicker than water. Let this mixture stand for 10 minutes, then boil it and stir it into the second batch. As with the first batch, the second batch will quickly become thin. Cover the drum containing the liquid, to retain heat and to exclude insects and dust. After about 3 hours when the temperature has fallen to between 60 and 65°C, stir in another 8 kg of crushed seedlings. Cover the drum again and leave it for 5 - 6 hours so that complete hydrolysis can take place. Once all the starch has been converted to maltose, no further hydrolysis will occur, so if it is more convenient, the rest of the process can be left until the next day.

Bring the juice to the boil and filter it through a cloth to remove the remains of the seedlings. Press the residue to squeeze out excess juice, then rinse it in a little water and press it again. The expressed liquid may be used instead of some of the water at the beginning of the process. This is a good way to recover the sugar. It is also a good way to save fuel, so when fuel is expensive or hard to obtain, quite concentrated juice should be used instead of water at the beginning of the process. The washed residue can be used for animal feed or dried and used as fuel.

Boil the filtered juice to concentrate the sugar. Foaming is often a problem in open pan boiling and the FAO manual describes a simple device for minimising this problem. A squat chimney' made of basket-work or sheet metal, is tied down in the pan. Foam rises inside the chimney and as it overflows down the outside, it breaks. This substantially reduces the amount of fat or oil which is traditionally used to control foaming. When foaming diminishes and is no longer a problem, the chimney can be removed.

As the concentration rises, so the boiling temperature of the juice will rise. Towards the end of the process, when there is a risk of burning the syrup, reduce the amount of heat from the furnace. Experience helps in knowing exactly when boiling should be terminated, but when drops of syrup falling off a test stick form fine threads of sugar, it is time to remove the pan from the fire. The final syrup should be quite thick and viscous when it becomes cold, but it should not set solid.

The final product is packed in bottles and plastic bags and is used in a range of products including baby foods, jams, bakery goods and confectionery. It is reported that Vietnam is now exporting some 70 tons of candies using maltose syrup each month to China which gives some idea of the scale of this artisan industrial sector.

* 'Sweetness from Starch' was written jointly by Nguyen K Quynh of the Root and Vegetable Research Centre, Hanoi, and John Cecil of FAO. It contains a detailed description of the process and the equipment needed to make maltose syrup in batches of between about 30 and 60 kg. Recipes for using maltose to make various products are also included. Send for a free copy to John Cecil, FAO, Via delle Terme di Caracalla, 00100, Rome, Italy.

The final product is packed in bottles and plastic bags and is used in a range of products including baby foods, jams, bakery goods and confectionery.