At the MBAA Regional in Philadelphia – Oct, 2012At the MBAA Regional in Philadelphia – Oct, 2012

Gary Spedding, Ph.D.Gary Spedding, Ph.D.

Managing Owner/Chemist & Sensory Specialist.Managing Owner/Chemist & Sensory Specialist.

Brewing and Distilling Analytical Services (BDAS) LLC.Brewing and Distilling Analytical Services (BDAS) LLC.

“Alcohol Measurement in Beer”

>Alcohol is generated relative to the amount of fermentable sugars in beer wort.>Is related to both wort specific gravity (SG) and wort RDF (Real or “true” degree of fermentation).>Accepted - 1 gram of alcohol requires 2.0665 g of fermentable extract.

[As originally determined: 2.0665 g sugar yields 1 g ethanol, 0.9565 g CO2 & 0.11 g yeast. Note: for equations below, 0.9565g & 0.11 g sum to 1.0665 extract NOT converted to alcohol.]

>Above values are used in varied published equations to determine alcohol strength.

Solving for alcohol determination by weight determinations (Karl Balling):

> [ABW: alcohol by weight (as w/w, grams of alcohol per 100 grams of beer). OG, original gravity & RE real or present extract.]

))100/0665.1(0665.2(

)(

OG

REOGABW

Brewers using a hydrometer - real extract can be approximated using OG and AE:

[(AE = apparent extract or attenuation – the value determined when alcohol is present) Note: this is only an empirical observation & applies only to traditionally fermented beers near 65 % RDF.]

Substituting into the above formula:

If the SG has been also been determined for the beer then the alcohol by volume can be determined with a correction to account for the specific gravity of the beer:

[Where, sp. gr: specific gravity, e.g., for the beer or pure ethanol.

Which simplifies to:

Variant equations are available but alcohol should be reported both % by weight (wt.) & by volume (vol.) to two decimal places. For reporting purposes brewers are allowed a tolerance of +/- 0.3% alcohol by volume.

“Introducing the Scandinavian Beer

Calculator”