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Publication Date: 2010-Nov-12
Document File: 6 page(s) / 127K

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We have developed a method using a combination of HPLC/IC analysis to accurately determine the RDF. This method, in addition, gives information about the nature of the sugar profile and the quantity of the other fermentables. This method will prove useful to understand the biochemical processes that take place during brewing and also the impact of conversion time, conversion temperature, enzyme dosage rates etc on starch conversion. It would also be possible to study how the different classes of wort compounds change in concentration during fermentation. This information can be used to make better enzyme solutions for brewing. It would also help understand how the nature of the starting material can influence the qualities of the final beer product and thus help in finding an optimum combination of the starting material to obtain the required type of beer.

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By Ricardo Gerlack


During the production of beer, the complex sugars in the grist (malted and/or unmalted grains) are converted to simple sugars in the wort by a process called mashing. The simple sugars in the wort are then anaerobically converted to carbon dioxide and alcohol by a process called fermentation using yeast. During fermentation, not all the sugars are converted to alcohol and carbon dioxide by the yeast.The grains used, the mashing profile, the yeast used and the fermentations conditions can influence the amount of fermentable sugars left in the beer.The amount of fermentable sugars left has an effect on the beer character since different styles of beer oftentimes have different amounts of fermentable sugars left in them.In brewing terminology, attenuation refers to the percentage of original extract that has been fermented.

Hydrometers are generally calibrated to measure the extract content of a water solutionthrough changes in the liquid density in relation to pure water. When used for wort, this calibration works true since wort does not contain alcohol. However in case of beer, which contains ethanol in addition to water, the reading will be skewed by the lower specific gravity of the ethanol, i.e,the hydrometer shows a lower density or specific gravity than what would be true if the alcohol would be replaced with water.This measured extract value is called apparent extract (AE). By evaporating off the alcohol and replacing it with distilled water, one can obtain the real extract (RE).When the AE of the beer is used to calculate its attenuation, the result is called Apparent attenuation (or Apparent Degree of Fermentation, ADF).The use of RE will give the Real attenuation (or Real Degree of Fermentation, RDF).

ADF or RDF is a very important parameter to be determined because it gives an indication of the alcohol content that can be expected in the final beer. In addition, the amount of residual extract in the final beer will give an indication of the mouthfeel or the body of the beer. Moreover, the calorie that the beer provides is dependent on its alcohol content and residual extract.

There are different methods to measure RDF. The commonly used European Brewing Convention (EBC)
8.6.1 calculates the RDF as follows:

ADF = 100*(OG - AE)/OG,
where OG is original gravity of the wort prior to fermentation, and AE is the apparent extract of the beer after fermentation.


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The RDF is then calculated from ADF as RDF=0.81*ADF.

This method does not take into account any mass loss during fermentation. In such cases, one uses the American Society of Brewing Chemists (ASBC) method which calculates RDF as
RDF = 100*(OG - RE)/((OG*(1 - (0.005161*RE))

Where OG is the original gravity of the wort prior to fermentation, and

RE is the real extract of the beer after fermentation.

The constant, 0.005161, is u...