dr. s.v. patil
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IMPROVING PROCESS
PERFORMANCE AND QUALITYOF 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:
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Introduction
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.
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VSI is also engaged in the development of new strains
of yeast for improving the alcoholic fermentationprocess.
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.
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Stress on Yeast cell
23% but 10% for
growth
>0.8 % w/v
35% w/v3.8-4.0
>100mg/l(Strain d.)
>500mg/l
>0.05% w/v
Lactic acid
pH
Sulfite
Sodium ion
Temp >350c
Acetic acid
Sugar
Stress may be synergistic
Ethanol
>0.3 % w/v Succinic acid
Caramel 1.0 % w/v
100 mg/l
Butyric Acid
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Inhibitory Components of Molasses
Low purity cane juice leads to formation of non-sugars inmolasses, which creates problem in the fermentation
process.
Molasses produced by double sulphitation process containsulphur 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 forfermentation as during storage sludge settles at bottom &entrapped gases like SO2 escapes.
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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.
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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.
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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.
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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.
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Bacterial contamination of molasses
* Bacterial contamination of molasses leads to poorfermentation efficiency, low alcohol yield & undesired
byproducts formation.
* Bacteria can also form gelatinous layer on the yeast
surface & reduce the active surface area resulting inslowing the fermentation progressively (Dextran formation
by L. mesenteroides ).
* If the contaminants are not checked in time, the
fermentable sugar gets depleted resulting in lowerproductivity.
* The common contaminants are Lactobaci l lus,
Leuconostoc , Act inomycetes, Zymomonas & wild
yeasts.
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* 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.
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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 themolasses 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.
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Volatile acids are also generated duringfermentation.
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.
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Volatile acidity and their effects on
yeast cell
• Acetic acid Destroy yeast
• Butyric acid membrane
• Propionic acid Decreases alcohol
• Valeric acid productivity of yeast
• Iso-valeric acid Decreases yeast growth
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Effect of Organic Volatile Acids on Fermentation
* Sudden increase in volatile acidity during fermentation isan indication of contamination.
* The presence of volatile acids above 5000 ppm inmolasses affect the yeast growth & activity adversely.
* It has also been reported that the presence of butyricacid above 100 ppm can reduce the rate of fermentation.
* Lower molasses is required to maintain the level ofresidual sugar to the desired limit, which leads to drop
in plant capacity.
* To overcome the adverse effect of OVA, the fermentationprocess should be operated with higher dilution rate.
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Microbiological analysis of molasses
Sr. No. Name of factory Total microbial
count
(cfu/g)
VA
(ppm)
1 Sakthi Sugars Ltd., 1.64 X 10 4 1114
2 Vishwasrao N. S.S.K.(1) 8.20 X 10 4 1585
3 Vishwasrao N. S.S.K.(2) 5.40 X 10 5 3107
4 R. B. Patil S.S.K.(1) 6.20 X 10 4 1542
5 R. B. Patil S.S.K.(2) 1.10X 10 5 2657
6 R. B. Patil S.S.K.(3) 1.00 X 10 5 1928
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Microbiological analysis of molasses
Sr. No. Name of factory Total
microbial
count
(cfu/g)
VA
(ppm)
7 R. B. Patil S. S. K. (4) 2.80 X 10 4 1200
8 Jawahar S.S.K. 4.20 X 10 4 1264
9 Ganesh S.S.K.(1) 8.80 X 10
5
332110 Ganesh S.S.K.(2) 8.20X 10 4 664
11 Ganesh S.S.K.(3) 1.06 X 10 4 921
12 Vishwasrao N.S.S.K.(4) 2.18 X 10 5 2764
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Graph - 2
0.0.E+00
1.0.E+04
2.0.E+04
3.0.E+04
4.0.E+04
5.0.E+04
6.0.E+04
7.0.E+04
Total Organic Volatile Acidity (PPM)
T o t a l M i c r o b i a l
C o u n t ( c f u / g )
Count1 1.5.E+03 1.5.E+03 1.1.E+03 1.0.E+04 1.2.E+04 1.1.E+04 3.2.E+04 7.0.E+03 1.1.E+04 2.4.E+04 6.0.E+04 2.0.E+03
Count2 1.6.E+03 8.0.E+02 1.0.E+02 1.9.E+04 5.0.E+03 1.0.E+03 2.0.E+03 3.0.E+03 1.5.E+04 4.1.E+04 5.0.E+04 1.2.E+03
Count3 8.0.E+02 1.8.E+03 9.0.E+03 1.4.E+04 3.0.E+03 1.5.E+04 6.0.E+03 1.0.E+03 2.7.E+04 3.8.E+04 6.0.E+04 2.6.E+03
Count4 2.0.E+02 1.2.E+02 2.0.E+01 7.0.E+03 1.0.E+03 4.0.E+03 1.0.E+03 3.0.E+03 6.0.E+03 6.0.E+03 1.0.E+03 6.0.E+02
664 921 1114 1200 1264 1543 1586 1929 2657 2764 3107 3321
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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 40O
C. Theresults are illustrated in the following table.
Our present study at laboratory scale shows that
the isolated yeast strain is temperature tolerant.
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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 4.20Alcohol % 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/ml 290 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
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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.
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Final alcohol concentration using various
Thermotolerant yeast strains
Sr. Inocu Ferm Time Alcohol % , (v/v)
No. Temp0 C
Temp0 C
Hr S. C.
Control
T. S. C.
20071
T. S. C.
20072
T. S. C.
20073
1. 32. 5 32. 5 27 8. 45 8. 11 9. 02 9. 32
2. 32. 5 37.5 41 8.45 8. 91 9. 02 9. 32
3. 32. 5 40.0 41 8. 11 8. 74 9. 08 9. 31
4. 37. 5 37.5 42 8. 74 8. 45 9. 01 9. 25
5. 40. 0 40. 0 41 Nil 6.17 7.54 7.25
S. C. – Saccharomyces cerevisiae
T. S. C. – Thermotolerant Saccharomyces cerevisiae
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Improving Alcohol Quality
• Due to gas chromatographic analysis we came toknow 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.
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Process Parameters of Analyser Column
Sr .No. Description OldParameters New Parameters(For Quality of
R.S.)
1 Fermented wash
feed, LPH
16000-17,000 14000-15000
2 Wash feed
temperature, OC
63-66 67-72
3 Alcohol, % 8.0-8.5 8.5-9.0
4 Bottom temperature,OC
80-81 82-83
5 Top temperature, OC 71-72 73-76
6 Vacuum, mmHg 390- 400 350- 380
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Process Parameters of Pre-Rectifier Column
Sr.
No.
Description Old
Parameters
New
parameters
1 Top temperature, OC 49-50 48-49
2 Bottom temperature, OC 61-62 64-66
3 I St condenser outlet water
temperature, OC
28-29 30-32
4 2 nd condenser outlet water
temperature, OC
30-32 35-40
5 Vacuum, mmHg 490-500 500-505
6 I St condenser reflux, LPH 6000-6500 6500-6800
7 2 nd condenser reflux, LPH 50-100 100-300
8 Reflux TA cut (total), LPH 100-120 30-40
Process Parameters of the Rectifier Column
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Process Parameters of the Rectifier Column
Sr.
No.
Description Old parameters New parameters
1 Steam flow, kg/hr 2300-2400 2400-2700
2 Pressure, bar (g) 2.2-2.3 2.3-2.4
3 Bottom temperature, OC 125-126 127-128
4 Top temperature, OC 99-100 100-101
5 LFO Ist cut temperature, OC 105-106 103-104
6 LFO IInd cut temperature, OC 109-115 105—112
7 HFO Ist cut temperature, OC 116-118 112-118
8 HFO IInd cut temperature, OC 118-119 120-122
9 LFO total cut, LPH 50-60 80-100
10 HFO total cut, LPH 10-20 20-40
11 Reboiler vent cond. Vent bottle cut,
LPH
- 30
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Impurities profile of RS by GC method
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