The high-test molasses is a heavy, partially inverted cane syrup (no sugar is yet removed) having a Brix of about 85. However, the term molasses is generally used to designate material from which sugar has been removed by crystallisation.
High-test molasses is produced instead of sugar, never in conjunction with it. The process is same as in raw sugar producing, i.e., milling, clarification, and evaporation, except that a much smaller amount of lime (about 0.25 lb to the ton of cane) is used to give a pH of 6.0 - 6.3. Two methods of inversion have been allowed. In the earlier years, sulphuric acid (1-2 gal per 100 gal, or 1-2 litre per 100 litre, of 55 Brix syrup heating to 195°F-200°F; 90°C-93°C) inverted the syrup until the polarisation showed zero; milk of lime was added to restore the 6.0 pH range, and evaporation to 85 Brix in vacuum pans completed the operation. The high heat, in this method, followed by liming, resulted in a dark red product that was quite viscous and contained two-thirds invert and one-third sucrose. Also, 3-5% of the sugars were destroyed by the high temperature in the presence of sulphuric acid.
The invertase method of inversion uses commercial dry granular yeast of a special strain manufactured for the purpose. The dry yeast is mixed in proper quantities in water acidified with HCl in a suitable container fitted with a mechanical mixer. This cream is fed to the evaporator discharge pumps or syrup storage tanks to give about 0.5 lb of dry yeast per 1000 gal (3785 l) of 55 Brix syrup. The temperature of inversion is that of the final syrup from the evaporators, 140°F (60°C). The crystallisers serve as inverting tanks (6 - 10 hours gives the desired inversion), controlled by apparent purity determinations to an end result of about 15 purity.
More common practice is to fully invert all the sucrose in 60% of the syrup, and add the uninverted portion in the vacuum pans for concentrations. The amount of yeast may be varied to speed up the inversion period. Evaporation to 85 Brix in vacuum pans yields a light brown product, low in ash, without the losses in sugars that occur with acid version. Broglio and Hulett report the production of HTM for export to Japan and the United Kingdom. The bakers' yeast. Saccharomyces cerevisiae, in slurry is added into the concentrated syrup of 53 ± 1 Brix, and kept in crystallisers for 6.5-9 hours. Then it is evaporated in a pan until approximately 70 brix. Necessary uninverted syrup is added into the pan to adjust for invert level. Then the final concentration brings the syrup to 83.5 Brix (refract). Their composition shows:
| Brix | 85.3 |
| Sucrose | 21.4 |
| Inverts | 55.0 |
| Total Sugars | 76.4 |
High-test molasses is used largely for distillery and as a commercial sweetener. Some high-test molasses is used for animal feeding. In some countries, tariff restrictions prevent the use of high-test molasses for human consumption.
High-test molasses is clear, light brown, and of controlled composition (as opposed to blackstrap, which is dependent on the cane from which it is made). A typical analysis follows:
| Brix | 85.0 |
| Sucrose | 27.0 |
| Reducing sugars | 50.0 |
| Ash | 2.25 |
| Water | 15.50 |
Chen, J.C.P. and Chou, C.C, Cane Sugar Handbook, Wiley and Sons, 1993
At the request of The South African Sugar Association, the management of Hulett's Mount Edgecombe mill accepted the challenge to manufacture High Test Molasses (HTM.) for export to Japan and the United Kingdom.
In 1938 a few thousand tons of this product had been produced in a small North Coast mill using the Acid Inversion technique, whereas this new contract specified the use of yeast as the inverting agent. The specifications set down by the buyers defined
The "C" massecuite house, consisting of 20 crystallizers of 1000 cu. ft. each, and 4 pans also of 1000 cu. ft. capacity each, was made use of for the inversion and concentration of the syrup. All crystallizer doors had to be sealed, and pipes, fitted with valves, welded to the bottom of each crystallizer for discharging the inverted syrup. These pipes in turn were connected to a pump which pumped the inverted syrup to the pan supply tank. A small tank was erected above the crystallizers where the yeast slurry could be injected into the flow of syrup, and from which the syrup could be discharged into any one of 18 crystallizers by a branched system of pipes and valves. The two remaining crystallizers were isolated from the circuit to act as receivers for the final concentrated HTM, before being weighed through an automatic Servo Balans. Two stainless steel tanks, each fitted with a stirrer and perforated air pipes, were erected for slurrying the yeast paste.
The yeast, Saccharomyces cerevisiae, or more commonly, Bakers Yeast, was obtained from two sources, namely Durban and Johannesburg. Only the daily requirement was ordered and the drums received were used in strict rotation so as to eliminate the possibility of deterioration. The activity of each consignment was carefully ascertained daily, by the method described later, and the quantity used per crystallizer adjusted when a fall off in activity was noted.
It was decided to concentrate the syrup in the evaporators to 53±1Brix, since above 55Brix the inversion rate falls off rather rapidly, and at too low a concentration it would not prove practical due to the increased volume of syrup, and the corresponding increase in evaporation that would he required from the pans.
The syrup was then pumped to the "C" massecuite house where 100 gallons of yeast slurry containing 85 lb. of yeast was injected into the flow of syrup per crystallizer. As it was not practical to use the cooling coils of the crystallizers as stirrers, care had to be taken to ensure a uniform addition of slurry to the syrup. To achieve this aim, the slurry tanks were calibrated to the volume of slurry to he used for each quarter of a crystallizer. The available retention time in the crystallizers could vary between 6 and 9 hours depending on the crushing rate of the milling tandem. Apart from the activity of the yeast, the retention time available had also to be taken into consideration when assessing the weight of yeast to be used per crystallizer. It was always the aim to over-invert the syrup in the crystallizers and then to correct for sucrose content by drawing uninverted syrup onto the inverted syrup in the pan while concentrating the inverted syrup was drawn into the pan, concentrated to approximately 70 Brix at 700 cu. ft., and a sample from the proof stick sent to the laboratory for analysis. from the data supplied to him by the laboratory, the pan boiler would add the calculated volume of uninverted syrup and concentrate to a refractometer brix of 83.50, each pan being boiled batch-wise.
The activity of the yeast was determined on a 55%, solution of refined sugar adjusted to 6.0 pH with ammonium citrate, containing 1 % yeast on solids, kept in a water bath at 55°C for 1 hour. The normal weight of the solution, clarified with 3 ml of lead acetate, was made up to 100 ml and polarised in a 200 mm tube. A yeast giving a reading of l5°S, representing 55% inversion, was considered acceptable. The range of activity could vary between 9°S (63% inversion) and 36°S (2% inversion).
The sample of HTM received by the laboratory from each pan was tested for
| Spindle brix (1 in 1) | 85.30 |
| Sucrose % | 21.40 |
| Reducing Sugars % | 55.03 |
| Total Sugars % | 76.43 |
| Total Sugars as Invert % | 77.56 |
| Tons HTM produced | 199,209 short tons |
| Total Sugars as Invert recovered % Sugars as Invert received | 98.46 |
| % uninverted syrup added to pans | 17 |
| Tons HTM produced per ton sucrose in clear juice | 1.4 |
Hulett and de Broglio, SASTA Procedings 1968, pg55