For convenience, any full size drum is referred to here as “vessel A” and any pan that can be put on the furnace as vessel B. When either of these vessels has to be emptied, liquid is removed using the ladle or a bucket until it is light enough to lift. The remainder is then poured out.
| Juice | Juice is the name given to filtered liquid that is ready for evaporation into syrup. It may contain anything from about 20% to about 50% of solids. |
| Sweetwater | Sweetwater is the material obtained by pressing and/or washing the residue left in the filter - either immediately following filtration of the juice, or after the residue has been washed. It will not normally contain more than 20% solids. |
| Syrup | Syrup is the concentrated product, containing 83 – 86% solids. |
Good quality seeds of a suitable variety of either rice or maize should be used. The seedlings should contain adequate quantities of the enzymes needed and at least 90% and preferably over 95% of the seeds should germinate.
The seeds should be germinated by soaking them in a sack for 24 hours. The water should be changed at least twice. The seeds, still in the sack should be kept in a cool place and wetted at least twice a day until the shoots are 2 – 3 mm long. At this stage, the germinated seeds should be set out under shade on a gently sloping piece of ground on a plastic sheet and under a sack or a sheet of dark plastic. An area of 1.0 m2 is needed for every 10 kg of seeds. The germinated seeds should be spread out evenly, producing a layer of 2 – 3 cm for rice and 3 – 4 cm for maize. The seedlings should be watered at least twice a day. After a week, the seedlings may be uncovered, but they must still be kept in the shade. In about 12 days, the seedlings will be about 10 cm long (with 5 cm roots). By that time, both maize and rice will have grown green leaves. The carpet of seedlings should be turned over and thoroughly washed before use. The roots require particular attention.
Slightly more than the required quantity should be pulped (in a mechanical pulper or with a pestle and mortar) shortly before use. Alternatively, the seedlings can be dried in the sun and the dried seedlings used instead. 1 kg of dried seedlings is equivalent to 2 kg of fresh seedlings.
In the following description, the quantities given are for the standard process as carried out in Vietnam, in which 50 kg of syrup is produced per batch. If a batch of a different size is wanted, the amounts should be changed proportionally.
Preparation of the “slurry batches” of rice, starch and water mentioned in this section.
The mixtures of rice seedlings and starch slurry can be prepared using any of a number of different materials - wet or dry starch, fresh or dried rice seedlings and either fresh water, limed water or sweetwater. Their composition is not critical, although the amounts of the ingredients should be approximately proportional to those shown below for the standard Vietnamese mix in which wet starch, crushed fresh seedlings and sweetwater are usually used.
| Approximate composition | ||
|---|---|---|
| kg dry material | kg water. | |
| 40 kg of wet starch, | 22 | 18 |
| 4 kg crushed fresh rice seedlings | 1 | 3 |
| 10 litres of warm water | 10 | |
| Totals | 23 | 31 |
The use of alternative ingredients will change the ratio of water to dry substance, so the proportions should be changed, as follows:
if dry starch is used instead of wet starch, only 25 kg of starch and 15 litres more water should be used.
if crushed dried rice seedlings are used instead of fresh seedlings, only 2 kg of rice should be used, but 2 litres more water should be added.
if sweetwater containing more than 10% of sugar is used, about 10% more sweetwater should be used than the indicated amount of water - both an additional litre of water in the mixture and 10 litres more in the amount of boiling sweetwater added to the first batch.
A description of the process
Please refer to Figure 12, a flow-diagram of the process, which follows this description.
Two batches each with 4 kg of crushed seedlings and either 40 kg of wet starch and 10 litres of water - or 25 kg dry starch and 25 litres of water - are made up in the shallow drums. Sweetwater, or a mixture of juice and sweetwater can be used in place of the water. If the starch is badly fermented, 500 ml of limed water should be added to each batch. The ingredients should be well mixed together and there must be no lumps of starch. One batch is placed in vessel A. 120 litres of water, sweetwater or a mixture of sweetwater and juice is boiled and added to this first batch of slurry. The mixture should be stirred until there is no sign of whiteness. After 5 – 10 minutes, this mixture should be quite thin and can be transferred into vessel B and brought to the boil without fear of it burning. Meanwhile, a second batch of slurry is put in vessel A and after a few minutes, the boiling contents of vessel B are added to it. As before, it should be stirred well during the addition of the boiling liquid. The resulting temperature should be about 80°C. In order to increase the concentration of the juice and reduce fuel costs, another batch of slurry can be included by boiling the mixture containing the first two batches and adding it to the third batch. After addition of the final batch, vessel A is covered and the mixture is left until it has cooled to within the range 62°C – 68°C (60°C – 65°C if dried seedlings are to be used). This cooling can take up to 4 hours, depending on ambient conditions.
A further 8 kg of crushed seedlings are then added and stirred in. The mixture is left for at least another 6 hours. A starch check should now be made (see the next section). If there is still some starch present, more seedlings should be added and the mixture left until all the starch has disappeared. If there is no starch present, the mixture is transferred to vessel B, briefly boiled and immediately filtered. The first material to pass through the filter should be filtered again.
This clarified material (juice) may be used to strengthen sweetwater for use at the beginning of the process, or it may be concentrated to produce syrup. As clarified liquid comes through the filter, if it is not needed for strengthening sweetwater, it is put back into vessel B and boiled. The foam “chimney” is put into position and tied down. Additional liquid is added as it comes through the filter. When there is enough juice in vessel B to make a batch of syrup (100 l of 40% solids juice or 200 l of 20% solids juice for a 50 kg batch) 20 grams of one of the chemicals for lightening the syrup is added.
Water is steadily boiled away and the liquid becomes more concentrated. As it becomes more concentrated, its character changes with increasing rapidity. The end point, which comes quite suddenly after an hour or more of evaporation, is determined by experience - the way the syrup falls off a wooden sample stick. It should be thick and syrupy, almost at the point of leaving threads as it falls. When the syrup is thick enough (in fact at 111°C) vessel B is removed from the heat and the finished syrup is poured into a dry drum to cool. As it cools, it becomes very viscous.
The seedlings collected in the filter sacks still contain a considerable quantity of juice. The excess liquid should be pressed out. The residue is then rinsed in some water in a drum and pressed once again. The final residue may be used as animal feed, or dried and used as fuel, or discarded. The sugars in the press water and the wash water are recovered by using them in sweetwater ,water at the beginning of the process.
To reduce the amount of fuel that is used and until familiarity with the techniques involved has been gained, it is best to aim for about 20% solids in the sweetwater/juice mixture used at the beginning of the process (it should be a little lower if dry starch or dried seedlings are used). This will give about 40% of solids in the juice. Each tune one carries out a cycle in which two slurry batches are added, the level of solids will increase by about 20% (20o Brix). Once thorough familiarity with the process has been achieved, trials at higher solids contents can be carried out. If with experience, higher solids contents can be achieved, savings in fuel will be dramatic - by comparison with the fuel requirements for evaporating juice with 23 % solids, juice with 40% of solids will only need half as much fuel to produce a kilogram of product and juice containing 50% of solids will require about 75% less fuel than juice with 23% of solids.
Figure 12. Flow Diagram of the Maltose Process.
* in order to increase the concentration of the juice and reduce fuel costs, a third batch of slurry can be included.
