Quality Control Methods Series

Prepared by Gary Spedding, Ph.D. and revised in 2014.

[Represented here are some methods and notes pertaining to the measurement of extract via specific gravity determination and appendices covering the use of refractometers in the brewing laboratory, alcohol determination by gravimetric distillation and via pycnometry.]

Extract by Specific Gravity 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 the 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 in 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. The Hydrometer: Specific gravity is also commonly measured by the use of a hydrometer. The heavier the liquid, in which the hydrometer is placed, the higher it will float. A scale placed on the narrow top of the hydrometer (the stem) can be calibrated in terms of specific

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gravity or concentration directly. There is one complication in the calibration of a hydrometer for beer, however. The weight of liquid in the meniscus formed by the liquid around the stem adds to the weight of the hydrometer itself in forcing the hydrometer into the liquid. Beer and wort have low surface tension compared to water or sugar in water and because of this they tend to form foam. Hydrometers reading Plato concentration in wort and beer are available from companies such as ERTCO (the Eveready Temperature Company!); they are designed for the surface tension of wort and they are read at the TOP of the meniscus. They are designed to be accurate within 0.02 °Plato in beer or wort. Less expensive hydrometers calculated to read Brix concentration of sugar water are available; they are designed for sugar water and are meant to be read at the bottom of the meniscus. If such hydrometers are read at the top of the meniscus, the resulting error is of the opposite sign as the error due to the difference in surface tension. Therefore, the overall error is less than either one alone. For this reason, Brix hydrometers can be used where a lower degree of accuracy than that obtained by the use of a special beer hydrometer can be tolerated. For best accuracy, a beer hydrometer should be used in the manner in which it was designed to be used. Because of the surface effects on the meniscus the hydrometer MUST be very clean. The hydrometer should be used on a “fresh surface”. The surface is provided by filling the hydrometer cylinder completely to the point where it overflows the top. Place a hydrometer into the liquid to be tested slowly and spin it slowly to keep it from touching the sides of the container. As the hydrometer settles to a steady level, refresh the surface with a little more of the test liquid. Wait about 30 seconds and read the level at the VERY TOP of the MENISCUS. Check the temperature of the liquid and make corrections as necessary (Tables of temperature correction from the AOAC are available and should be supplied with any reputable supplier of such instruments). The scale on the hydrometer gives rough corrections; a chart for more accurate corrections should be used. A dirty hydrometer placed in a liquid with an improperly formed meniscus can easily be off by 0.2 °Plato or more. A listing of Tips for Obtaining Accurate Hydrometer Readings is Provided Below (Table 1.)

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Table 1. Summary of Tips for Obtaining Accurate Hydrometer Readings 1. Use a clean dry hydrometer 2. Use a smooth, clear cylinder or jar “for liquid testing”. This container should be dry or Well rinsed with a portion of the sample prior to measuring a fresh portion. 3. Thoroughly mix the sample before testing. Use a stirrer that will reach the bottom of the sample container. 4. Immerse the hydrometer slowly in the liquid to a point below which it naturally sinks. Do not immerse the hydrometer more than 1/8th”. 5. Do not take a reading until the hydrometer and liquid are at rest and free from air bubbles. 6. Confirm that the hydrometer and the liquid to be tested have equivalent temperatures. 7. Confirm that the temperature of the liquid is equivalent to that of the surrounding atmosphere. When temperature differences are necessary, use correction tables to approximate the reading. 8. If possible, use a hydrometer that is intended for the liquid to be tested. Incorrect readings will be obtained for a liquid with the same density but different surface tension than the liquid for which the hydrometer is specified. 9. Hydrometers of equivalent dimensions may be compared with each other even if the liquid used differs in surface tension from the specified liquid, but comparisons of dissimilar instruments, in such a liquid, must be corrected for the effect of surface tension. 10. Overflow the cylinder immediately before taking the reading to avoid errors due to spontaneous changes in surface tension, skimming and formation of surface films of impurities from apparatus, liquid or air. 11. To read the hydrometer, bring the eye (preferably from below) to the level of the surface plane of the liquid. Read the point on the scale as directed. 12. Avoid parallax errors by aligning the near end of the mercury column with the portions of sample on either side of the stem and the sample seen through the capillary. When your eye is in this position, the line of sight is normal to the stem. [Table 1 has been Adapted from a Condensed data set prepared, according to VWR Scientific, from NIST (NBS) Circular No.16.]

Protocol (for Laboratory Worts):Measure the specific gravity and Brix or Plato of the laboratory wort or sample as directed. (If using your wort or beer samples follow directions accordingly and record readings.) [If you have made the Laboratory wort (a simplified procedure is available upon request) the extract present in the 50 g of malt used to make the wort can then be calculated in percent by weight of the malt as follows:P  [ M  800] % Extract , as is  100  P Where, M is the moisture in the malt and P is the extract, 0Plato, of the wort. {Fully detailed instructions for laboratory or “Congress Worts” are to be found in official manuals such as the Methods of Analysis volume or CD-ROM of the American Society of Brewing Chemists (ASBC).}

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This calculation (above) makes the assumption that all of the water in the wort is due to the 400 g of water added and the moisture present in the malt. Knowing the exact weight of water in the mash and the percentage of extract in the wort (0Plato), the extract provide by the malt can be calculated and expressed as a percentage of the 50 g of the malt used.] For beer alcohol and extract calculations [using SG or Plato values determined for wort Original Extract (OE) and final or apparent gravity (or real extract via calculation or testing of a dealcoholized beer sample)] BDAS, LLC has presented a series of talks and papers detailing the approaches to take using such data. See: http://brewersdigest.net/digital.html for a published version in the relaunch inaugural edition. Or contact us for details at: [email protected].

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Appendix I

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. Refractometers and Brewing: The use of a small hand held refractometer in brewing was described by Frank Roberts and Tod Stewart both from the Wahl-Henius Institute of Chicago. They presented a report at the 1950 ASBC meeting and this was published in the Proceedings of that meeting. More accurate immersion type refractometers had been used in brewing for some time, but their use required carefully controlled temperatures and very careful calibration. Some handheld units available are temperature compensated instruments. Nevertheless it is still recommended to bring samples to room temperature before measuring samples. Long time experience has shown that due to the complex composition of beer (with proteins and minerals present) the refractometer reads a little too high with wort samples. The readings are on the average 1.04 times the actual sugar concentration of the wort. To use a refractometer for monitoring runoff during brewing or wort concentrations in the kettle, you would therefore divide the reading by 1.04. The actual figure varies a little bit with conditions in different breweries; it might be that the actual reading is from 1.02 to 1.05 times higher than the actual value. [NOTE: BDAS, LLC is currently undertaking a project to reevaluate the use of Refractometers for both wort and beer measurements and then to apply that information to alcohol determinations. Please keep in touch with us for further developments in this area.] Use of the refractometer does give a very quick and easy and fairly accurate value. When using a typical handheld refractometer, fill the sample section with wort and hold the instrument up towards a good light source. Each line is equal to a set value such as 0.2 Brix or Plato (follow your own instrument parameters accordingly). Estimate to the nearest 0.1 (or as defined for the instructions with the instrument). Today reliable electronic, portable

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“benchtop” models are available for less than $1000.00 and may be used (fill the chamber and makes the determinations as instructed by the supplier). With any two independent measurements made on beer one can theoretically calculate two different characteristics of the beer, specifically alcohol and real extract. By combining refractometer readings with hydrometer readings, one can estimate alcohol and real extract in beer. Very accurate determinations can be made with an accurate refractometer. The method has to be calibrated for just one particular brand of beer for high accuracy. Roberts and Steward published formulae, which give less accurate values for a range of beers. Measure the apparent extract with a hydrometer and record it as “B” for Balling. Measure the apparent extract with a refractometer and record it as “r” for refractometer. Use the following equations with your data.

Calculate alcohol by weight by : Calculate real extract by :

A  1.09 r  1.13 B E

And: Calculate original extract in wort :

 0.49 r  B OB  2.59 r  1.69 B

The authors found that alcohol was usually within 0.2% of the value determined by more exact methods. If the original extract, (here defined as OB) OB of fermenting wort is known, the apparent extract or Balling can be estimated from the refractometer reading, r, by the following formula:-

B  1.53 r  0.59 OB Again note BDAS, LLC is reevaluating the use of refractometers for such extract determinations. We do, however, note another paper on the topic: “Determination of Original Gravity and Alcohol Content of Dark Starkbiers with the Refractometer” by Peter Koestler and W. Hagen. MBAA-TQ Vol 36 (# 2): pp231-233, 1999. This might be of use and interest for those using or interested in the use of refractometers for brewery work. Additional details are to be found in the MEBAK (European Official Methods of Analysis) volumes. The nomograms require either the gravity or density values to be determined along with the refractive index!

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Appendix II

Alcohol By Distillation (Gravimetric Distillation) Alcohol has been traditionally measured by distillation. The alcohol is boiled out of the beer and collected by condensing it. Along with alcohol and water some other volatile components of the beer will be distilled. The concentration of alcohol in the distillate must be estimated and then converted by calculation into alcohol content of the beer. One way of estimating alcohol content in the distillate is to measure the specific gravity of the distillate and use standard alcohol tables to determine alcohol content. We use official tables including one (for 60 °F work) derived from an ASBC table which was in turn derived from U.S. Bureau of Standards tables and, for work at 20 °C, the OIML Legal Metrology tables from Europe. ASBC Tables Related to the Determinations on Wort, Beer, and Brewing Sugars and Syrups are also available (recently republished by the ASBC). [Note: Today we use volumetric distillations in place of gravimetric distillations and must correct appropriately for the alcohol by weight in such samples. Details of this may be obtained upon consultation with us or from viewing our papers on the topic of alcohol determinations and calculations.] Materials and Methods:Apparatus:-

1) 2)

Distillation Apparatus. Distillation apparati consist of a sample flask, an entrainment (or Kjeldahl) trap, a condenser and receiving flask. Bunsen burner or hot-plate unit, wire gauze, flask stoppers, rubber tubing, clamps, and a container for cooling water. A cloth soaked in iced water is used for “damping” the sample flask during overvigorous boiling.

Protocol:1)

Use a sample of exactly 100 g of beer. Weigh 100 g of decarbonated beer into a previously tared distilling flask and rinse with/add 50 mL of water.

2)

Connect the flask to the distillation setup along with a preciously tared receiving flask. Distill alcohol and water into a receiver until just under 100 mL is collected (94-96 mL). It will be necessary to keep a close watch on the boiling beer. Until most of the alcohol has distilled over the boiling can get so vigorous it may reflux over into the distilling arm. The vigorous boiling can be controlled or “dampened” by touching a cold damp cloth briefly onto the sample flask. After a while the boiling

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will “settle down” and can be continued until the required volume has been collected in the receiving flask. 3)

Bring the total weight of the distillate back to exactly 100 g with water and mix well.

4)

When cooled bring the few mL of liquid/syrup left in the distillation sample flask back to exactly 100 g and then this can be used to determine the real extract of the beer. [This can be determined by, densitometry or via pycnometry.]

5)

Determine the specific gravity of the distillate (e.g., by density meter or pycnometry at 20 °C) and determine alcohol by weight from the specific gravity. Since both weights were exactly 100 g, the alcohol in the beer will be the alcohol in the distillate (alcohol by weight). See the table of conversion of Specific Gravity to Alcohol by Weight in Water-Alcohol Mixture.

Calculation: Alcohol by volume can be calculated from alcohol by weight as follows:-

Alcohol , % volume 

Alcohol , % weight  Specific Gravity of Beer 0.791

The Manuals of Methods of the ASBC (American Society of Brewing Chemists); the EBC (European Brewery Convention); and, the IoB (Institute of Brewers - now the IGB), may be consulted for full details of calculations needed to determine other parameters related to the alcohol content, the gravities, calories, and extract contents of finished beer. Moreover we also have papers detailing such calculations. See also Appendix III on pycnometry (below).

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Appendix III

Alcohol Determination by Pycnometry. The amount of alcohol present in a solution can be determined by measuring the specific gravity of the liquid and relating the gravity to standard tables of conversion of specific gravity to alcohol by weight in water-alcohol mixtures. One simple but very accurate way to do this is through the use of a specific volumetric container called the pycnometer and the use of a multi-place analytical balance. The pycnometer is a small flask with a very narrow opening at the top, which is drilled to accept a snugly fitting ground glass stopper. After the flask is filled and the top fitted on (excess liquid being displaced by the stopper), the flask is wiped dry and is ready to be weighed. Because the top opening is so narrow, the volume contained in the flask is always exactly the same within a very small error limit. Specific gravity is the density of an unknown liquid compared to (divided by) the density of water. Density is weight/volume. Because the volume in the pycnometer is always almost exactly the same, the specific gravity of a liquid is equal to the weight of the liquid, which fits in the pycnometer divided, by the weight of water, which fits in the pycnometer. As density is related to temperature, the pycnometer and contents need to be equilibrated to a set temperature (usually exactly 20 0C), and must be dried quickly and thoroughly before weighing. Protocol to measure the specific gravity by means of the pycnometer. 1.

Obtain the weight of the pycnometer (flask and its matching stopper) on an analytical balance (to 4 to 5 decimal places if possible).

2.

Fill the pycnometer with water at 20 0C (and/or equilibrate the pycnometer and contents to 20 0C in a water bath). Weigh the (thoroughly dried) pycnometer again quickly. This allows calculation of the weight of water in the pycnometer at 20 0C.

3.

Rinse and then fill the pycnometer with the liquid to be measured.

4.

Equilibrate to 20 0C and then dry and weigh quickly again. This allows determination of the weight of the liquid at 20 0C.

5.

Divide the weight of the liquid by the weight of water to obtain the specific gravity of the liquid at 20 0C: Specific Gravity 

weight of unknown liquid at 20 0C in a certain volume weight of pure water at 20 0C in the same volume

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6.

Determine alcohol by weight from the specific gravity of the distillate using the ASBC* or OIML* Tables (consult us for details or read our Brewers Digest 2013 paper) or use the equation below.

* Tables of Conversion of Specific Gravity (or Density) to Alcohol by weight in WaterAlcohol Mixture. Note, A distillate sample should be brought to a set weight, e.g., 100 grams, prior to filling the pycnometer. The final weight should be equal to the weight of the mixture (e.g., corn mash or beer etc.,) distilled in order to relate back alcohol to the weight of distilled mash/beer etc. Alternative Calculation Method for Alcohol Determination. The specific gravity of the distillate can be converted to the corresponding alcohol content as % (wt/wt) using the following polynomial: Alcohol content [% (wt/wt)] in distillate = 517.4 (1-SG) + 5084 (1-SG)2 + 33503 (1-SG)3 NOTE HOWEVER THAT THIS RELATIONSHIP BREAKS DOWN ABOVE 25% ALCOHOL BY VOLUME (we discuss this important issue extensively elsewhere). Alcohol Content from Weight Basis to Volume Basis. [To convert to Alcohol as % (v/v) see for example EBC Analytica 9.2.1.] The equation desired is as follows (see also under Appendix II):-

Alcohol % (v / v) 

Alcohol % ( wt / wt )  Specific gravity 0.791

Where 0.791 is the specific gravity of ethanol at 20 0/20 0C. [As usual these notes now combined for the first time in 2014 form a work in progress with changes made on an ongoing basis. Specifically at this time we are reviewing methods for use with modern and inexpensive refractometers as standalone measuring devices. Please keep in touch for future developments on all this neat stuff.] Gary Spedding, Ph.D. Managing Owner BBAS, LLC, Lexington, KY. January 2014.

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