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:

[email protected]

mailto:[email protected]

mailto:[email protected]

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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




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


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


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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