ETHANOL DETERMINATION BY DISTILLATIONBy Sreermya.S

Lecturer,

Dept Of Biotechnology, Mercy College,

Palakkad

Many microorganisms, notably yeasts and bacteria, extract energy from their food (glucose) by fermentation. The overall chemical reaction for this is: C6H12O6 2CO2 + 2CH3CH2OH (ethyl alcohol).

It was this process which Louis Pasteur studied, leading to a biochemical understanding of biological processes. Humans have known about and utilized the process of fermentation for many thousands of years. CO2 liberated by yeast cells doing alcohol fermentation causes bread to rise.

The Egyptians and many subsequent civilizations have fermented grains such as barley to break the starch down to malt (maltose), then glucose, and finally alcohol. For at least that long, people have known that various fruits, especially grapes, could also be fermented to produce alcoholic beverages.

Distillation unit

The amount of extract present in a wort or mash sample is determined by measuring the specific gravity of the sample.

Generally a higher specific gravity relates to a higher concentration of the wort or mash. The, readily available, tables of conversion relating the concentration of sucrose (sugar) to specific gravity which brewers often rely on today is that developed by Plato around 1900. This very exact table replaced a less accurate one developed by Balling. Wort concentrations in percent sugar by weight (wt/wt) derived from Plato’s table should be called degrees Plato (°P), but sometimes the term Balling is used even though Balling’s table is not used for the determination.

Other industries also use Plato’s table to calculate percent sugar by weight and call it degrees Brix.

For all intents and purposes Balling, Brix and Plato all mean the same thing – percent sugar based on Plato’s table.

Pycnometry: Plato measured specific gravities by the use of a pycnometer, still a very accurate method. Pycnometry is covered in a separate protocol note sheet presented below and further details are to be found there.

Specific gravity is the expression of density of an unknown liquid compared to the density of water. Because the density (weight per unit volume) of a liquid changes with temperature the temperature at which weights are taken in Pycnometry has to be specified and controlled. Most countries accept 20 0C as the specified temperature. The specific gravity of a wort sample is obtained by pycnometry at the specified temperature and th corresponding percentage of extract (equivalent) to sucrose) is determined from Plato’s table.

The accuracy of the measurement depends on the accuracy of the specific gravity measurement. A change in specific gravity from 1.0151 to 1.0152 results in a change in extract of 0.03 °P (3.85 to 3.88). A change in temperature of just 1 °C results in a change I calculated extract of about 0.06%. Controlling the temperature within 0.5 degrees and measuring weight to within 10 mg (0.01 g) in a 100 mL volume should give results accurate enough for most purposes in a small brewery.

Hand Refractometers for Brewing and Distilling Operations. Refractometers can be used to give an indication of the

sugar content of Distiller’s mashes, and molasses samples and also for Brewer’s worts.

Refractometers were designed for use in the juice and soft-drinks industry and are calibrated in Brix, which is percent sugar, the same as °Plato (used by Brewers).

It should always be remembered that they were designed to measure sugar content in pure sugar solutions and that some calibrations and factors need to be considered when using refractometers in other solutions such as mashes and worts.

Nevertheless modern refractometers are easy to use can be useful for monitoring fermentation performance and relative sugar contents in final products.

Fractional distillation (collecting the distillate in aliquots rather than the whole solution). This is the source of liquors with higheralcohol contents.A liquid must be brought just slightl above its boiling point before bubbl initiation can begin to start it boiling. As a bubble of vapor appears within the liquid, I may do one of two things: if it is below minimum size, it will collapse because of the surface tension of the liquid, or if it is large than the critical size, grow and rise to th surface of the liquid. If a liquid, which is free of solid impurities or dissolved gases, I heated slowly, a temperature much above th boiling point can be reached without any boiling actually taking place. Thi superheating occurs because extra energy I required before bubble formation is initiated. If a bubble should start to form in such a superheated solution, it might suddenly growith almost explosive violence enough to shatter the container.

This problem, called bumping, can be overcome by adding boiling chip, a piece of porous material, to the liquid before it is heated to the boiling point.

The pores act as built-in bubbles so that a June 19, 2011 10 liquid cannot superheat. As the distillation proceeds, the air in these pores is replaced by vapor of the distilling material, but this vapor cannot condense because the temperature of the liquid is just slightly above its boiling

ARRANGEMENT OF FRACTIONAL DISTILLATION

PROCEDURE

Pour beer into 100 mL volumetric flask (use the one labeled 7 as its mark is high u on the neck.) Use a 1 mL Tensette pipet to suck foam out of neck. Fill to the mark or just above. Stopper and place in 20°C water bath.

2. While beer is attemperating pull microwave oven away from wall. Place jack stand on top of microwave oven. Elevate so that top of platform is about 8” above top of microwave. Place 500 mL mantle on top of jack stand with control knob facing about 30° to the right of forward.

3. Place Cole-Parmer ringstand (with white base) to left of microwave oven. Base shoul be behind rod and rod should carry two clamps oriented away form base i.e. towards front of microwave.

4. After beer has attemperated, suck out excess beer and foam so level is at the mark.

5. Fill two 25 mL flasks with DI water to near the marks.

6. Pour beer into 500 mL distillation flask. Rinse with two 25 mL portions of DI water Add a couple of carborundum boiling stones.

7. Place distillation flask in mantle. Stabilize with clamp on mantle rod.

8. Place Kjeldahl trap in flask neck. Stabilize with clamp on mantle rod.

9. Connect bridge adapter to top of trap. Be sure thermometer port is plugged with glass

stopper.

10. Rinse 100 mL volumetric flask with DI water and place in 500 mL beaker on counter

top.

11.Place straight adapter on end of 400 mm condenser and while holding it in place lower its end into volumetric flask. Place condenser into two clamps on Cole Parmer ringstand without tightening. Simultaneously lower jack and position receiver, ringstand and bridge adapter angle so that bridge adapter mates with top of condenser. Adjust postitions so that all glass joints are tight and so that there is a little clearance between the straight adapter and the mouth of the volumetric flask. Tighten the clamps.

12. Make and check the cooling water connections. 13. Surround the receiver with ice cubes in a little water,

turn on the cooling water and set the mantle control to 10 for 10 minutes, then lower heat setting to 6. There should be some reflux from the neck of the flask during this time.

15. Boiling should commence within a minute or so and reflux from the walls of the Kjeldahl adapter should start. If all goes well, the alcohol in this reflux should collapse the foam. If it doesn’t, well that’s what the trap is there for.

16. After 20 minutes (total) foaming should be under control and alcohol should be seen dropping from condenser tip into straight adapter. Advance heat to 7. After stabilizing, condensate should appear at about 10 - 20 drops per minute.

17. After 1 hour (total) raise heat to 8. Check tightness of glass joints. 18. During distillation tare pycnometer, if pycnometer is being used, and obtain weight measurement with DI water at 20°C 19. Collect just under 100 mL of distillate. This should take about 2 and three quarters

hours. 20. Place volumetric flask in water bath. After attemperation, make to mark with DI

water. Mix throroughly. Measure and record density, specific gravity and OIML ABV. Find ASBC ABV from ASBC tables. Calculate ABW from grams/100 mL in ASBC tables.

21. Transfer residue from distillation flask to same volumetric flask. Rinse distillatio flask with 25 mL portions of DI water. Place in water bath and make to mark with DI water. Measure and record density, specific gravity and °P.

22. Measure and record specific gravity, density and °P of beer. 23. Do the sums!

THANK YOU