which it grows and transforms them into many things, including the soluble disaccharide — also known as sucrose — as well as fructose and glucose. Other products include lignin, cellulose and hemicellulose, all necessary for the plant’s growth. Between 3540% of the sugar produced is consumed by the plant itself as a source of energy for cell expansion, division, nutrient uptake and maintenance during plant development.1 The concentration of sugar in the cane, the yield of sugarcane by surface cultivated and the yield of sugar per mass of cane cultivated will be explored in detail in a future article. For now we move our attention to the sugar mill, where the cane is crushed and pressed in order to extract its juice and the sugars that are dissolved in it. It is here at the mill where we can encounter a variety of aerobic, microaerophilic and anaerobic bacteria. Most all of these bacteria have negative effects on the fermentation process, the worst ones being Leuconostoc mesenteroides and Leuconostoc paramesenteroides. L. Mesenteroides is a very dangerous threat because it polymerizes sucrose molecules into dextran, a form of sugar which is un-fermentable, meaning that the actual alcohol yield from fermentation will be much lower than the practical yields observed in the absence of this bacteria. Another cause for reduced yields is caramelization of sugars due to the heat applied to boil the freshly-pressed cane juice. The boiling of the juice is a necessary part of the process of producing sugar, since it removes the excess water from the solution until there is not enough remaining liquid to keep all the sugar dissolved and thus the sugar is able to be removed in the form of crystals. When buying concentrated cane juice, High Test (HT) molasses or other forms of cane syrups, suppliers are likely to quote only “sugars” or “total sugars,” as opposed to only the fermentable sugars, which distillers are interested in. Thus, it becomes the distiller’s responsibility to quantify fermentable and nonfermentable sugars, in order to determine fermentation efficiencies and to have better quality and cost control.
HOW TO MEASURE SUGARS FROM SUGARCANE (NOT FROM BEET) The easiest method is to have the analysis conducted at the sugar mill, by trained personnel whose livelihood depends on their ability to carry out those tasks. Most craft DSPs, however, do not even register on the sales’ radar of the mills, thus Fermentation they are unlikely to have the leverage efficiency based on Stoichiometric Yield to request — and be provided with — those reports. 100% The next easiest alternative is to have a qualified lab do the tests, but this 94.6% involves shipping delays plus the cost of the tests themselves, making it an 94.0% 1 Hall, D.O., and Rao, K.K.(1999): Photosynthesis, Cambridge University Press WWW.ARTISANSPIRITMAG.COM
expensive and impractical solution in many cases. There are several methods available for the determination of sugars, each method requiring a different level of knowledge and varying degrees of laboratory equipment dexterity. Below is a brief listing of methods, those interested in learning more about them can easily search the internet for procedures and, in some cases, even instructional videos: >> Determination of Sucrose by polarimetry (Clerget Method): a. Invertase Method or b. Jackson and Gillis' Method IV >> Determination of Reducing Sugars: a. Lane and Eynon's Volumetric Method or b. Munson and Walker's Method or c. Berlin Institute Method >> Determination of Dextran: a. Wet Chemical Methods, such as the Haze Method, AOAC Method (Roberts Copper Method) and various enzymebased Methods and b. Proton Nuclear Magnetic Resonance (highly-specialized laboratory only!) The presence of dextran should always raise a red flag, especially because it can be a sign of an active contamination that will only get worse when the wash is prepared with the water (L. Mesenteroides will actively attack all sugars in the wash once the osmotic pressure is reduced by the addition of the wash water). If there is an active contamination, it can be addressed via the use of antibiotics or by pasteurizing the wash prior to the pitching of the yeast.
YIELDS OF LARGE DISTILLERIES Once you find the amount of fermentable sugars in your wash, you can then use the previously-discussed formulas to determine the maximum theoretical and maximum practical yields. Then measure the actual amount of alcohol you produced and see how far your results are (I will discuss distillation efficiencies in a separate article). The following table shows average values from large distilleries that produce sugarcane ethanol. These values represent yields that
Fermentation yield in tons of anhydrous ethanol (100%) per ton of fermentable sugar
Fermentation yield in liters of anhydrous ethanol (100%) per ton of fermentable sugar
Observations
0.511
648
Maximum theoretical value, not attainable in real life
0.484
613
Maximum practical yield
0.481
609
88.0%
0.450
570
Average operating range for large distilleries
86.0%
0.440
557
Below average yields at or below this point
89