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IMPROVING PROCESS PERFORMANCE AND QUALITY OF ALCOHOL IN MOLASSES BASED DISTILLERIES. M. L. Kadam 1 , R. V. Burase 2, S. V. Patil 3 Vasantdada Sugar Institute, Manjari (Bk.), Pune 412 307, India. Author for correspondence: sanjay01356@hotmail.com.
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IMPROVING PROCESS PERFORMANCE AND QUALITY OF ALCOHOL IN MOLASSES BASED DISTILLERIES M. L. Kadam1, R. V. Burase2, S. V. Patil3 Vasantdada Sugar Institute, Manjari (Bk.), Pune 412 307, India. Author for correspondence: sanjay01356@hotmail.com
Indian Alcohol Industry mostly consumes sugarcane molasses as the raw material. Indian Molasses produced by double sulphitation method is a complex medium & inferior in quality. Various components in molasses have direct impact on fermentation process. Particular attention needs to be given to the microbiological quality, volatile acidity, sludge & caramel content of molasses. The correlation between the volatile acidity & bacterial contaminants has been investigated with respect to quality of molasses. Introduction
VSI is also engaged in the development of new strains of yeast for improving the alcoholic fermentation process. Various thermotolerant yeast strains have been isolated & tested . At laboratory scale, a potential thermotolerant yeast isolate has shown promising results at 40OC. Based on GC investigations of various distillation fractions at VSI, member distilleries were advised to make modifications in the distillation process operations leading to substantial alcohol quality improvement.
Inhibitory Components of Molasses • Low purity cane juice leads to formation of non-sugars in molasses, which creates problem in the fermentation process. • Molasses produced by double sulphitation process contain sulphur compounds, which are toxic to the living organisms. • Fresh molasses lowers the fermentation efficiency due to high sulphite content. • Old molasses also shows poor recovery due to formation of complex compounds by reaction of reducing sugars with nitrogenous bodies. • Therefore, 1-2 months stored molasses is ideal for fermentation as during storage sludge settles at bottom & entrapped gases like SO2 escapes.
Molasses Storage • Molasses should be properly cooled in the sugar factory before it is pumped to the molasses storage tank. • Molasses storage tanks should be cooled by external surface cooling. • Molasses in the storage tank should be routinely re-circulated. • Molasses tanks should also be properly cleaned at least once in a year.
F/N ratio • Higher F/N ratio is desirable in molasses. • F/N ratio varies from 0.7 to 2.5. • Generally, above 1.2 F/N ratio is suitable for smoother fermentation. • The low F/N ratio results in higher osmotic pressure. • To minimize adverse effect of osmotic pressure on yeast, it is desirable to operate fermentation with higher dilution rate.
Ca/inorganic ash content • Inhibitory at higher concentrations above 2.0 % Ca can cause flocculation.Sludge content • Increasing trend :15 -20 %, reduces fermenter effective volume. It gets recycled in cell recycle system and also results in alcohol loss.
Caramel and alcoholic fermentation When sugar is exposed to higher temperature for longer period, it gets caramelized in sugar manufacturing system. Caramel gives dark brown colour to molasses. Caramel inhibits the fermentation process, higher caramel increases the fermentation time. Caramel content above 1 % in molasses can slow down the activity of yeast. To overcome adverse effect of caramel content, run the fermentation process higher dilution rate. Caramel in molasses is indirectly measured as colour (Optical density) of molasses.
Bacterial contamination of molasses*Bacterial contamination of molasses leads to poor fermentation efficiency, low alcohol yield & undesired byproducts formation.* Bacteria can also form gelatinous layer on the yeast surface & reduce the active surface area resulting in slowing the fermentation progressively (Dextran formation by L. mesenteroides).* If the contaminants are not checked in time, the fermentable sugar gets depleted resulting in lower productivity.* The common contaminants are Lactobacillus, Leuconostoc, Actinomycetes, Zymomonas & wild yeasts.
* Due to viscous nature of molasses, the number of microorganisms are not homogenous throughout the medium.* For microbial analysis of molasses- Nutrient agar, McClesky- Favile medium, Wort agar & Shapton agar were used. *Total microbial count varies: 102 - 107 cfu/g * Compete with yeast for FS*Use of antibiotics or anti-microbial products.
Components of Organic Volatile Acids Acetic acid, Formic acid, Propionic acid, Butyric acid, Mallic acid, etc. Acetic acid concentration is major (around 80%). The concentration level of these acids differ in the molasses samples. Formation of OVA depends upon soil conditions, geographical locations, method of harvesting, premature cutting & processing of cane and processing methods in sugar mills, etc.
Volatile acids are also generated during fermentation. Conversion of ethanol to acids due to presence of Acetobacter & Lactobacillus. Higher residence time and presence of aerobic conditions can also lead to oxidation reactions forming acids.
Acetic acid Destroy yeast Butyric acid membrane Propionic acid Decreases alcohol Valeric acid productivity of yeast Iso-valeric acid Decreases yeast growth Volatile acidity and their effects on yeast cell
Effect of Organic Volatile Acids on Fermentation* Sudden increase in volatile acidity during fermentation is an indication of contamination.* The presence of volatile acids above 5000 ppm in molasses affect the yeast growth & activity adversely.* It has also been reported that the presence of butyric acid above 100 ppm can reduce the rate of fermentation.* Lower molasses is required to maintain the level of residual sugar to the desired limit, which leads to drop in plant capacity. * To overcome the adverse effect of OVA, the fermentation process should be operated with higher dilution rate.
New Yeast Cultures • Several yeast strains have been isolated from various sources and being used by member distilleries. • One strain (VSI-SC1011) has been found to be effective in high volatile acidity conditions. The results are illustrated in the following table. • At laboratory scale, a potential thermotolerant yeast isolate has shown promising results at 40OC. The results are illustrated in the following table. • Our present study at laboratory scale shows that the isolated yeast strain is temperature tolerant.
VSI-SC1011 Performance under High Volatile Acidity Conditions Before use of After use of VSI-SC1011 VSI-SC1011 V. A. in F1 1800 ppm (Avg) max. 850 ppm. pH 3.80 to 3.90 4.00 to 4.20 Alcohol % in F4 8.30 % (v/v) 9.40 % (v/v) R.S. in F4 1.30 % (w/v) 1.00 % (w/v) Cell count in F1 200 X 106 cells/ml290 X 106 cells/ml Cell Growth Normal Fast Acid Consumption 80 lit/day 40 lit/day Average production 42000 lit/day 45500 lit/day Continuity 4 Days min- 15 days
Thermotolerant yeast strains for alcoholic fermentation*The fermentation at temperatures around 400C has advantage of significant savings on the operational costs of cooling the fermenters in the distilleries.*In spite of the economical importance, there are very few reports on the selection of yeasts that are able to grow and ferment at higher temperatures.
Final alcohol concentration using various Thermotolerant yeast strains
Improving Alcohol Quality Due to gas chromatographic analysis we came to know impurities content in fermented wash and various fractions of distillate. Based on impurities profile of various samples, feed flow rate, temperatures & pressures of columns, recycle flows and impure cut flow rates are adjusted.
