To determine the brewery produced beer contains much alcohol, just before and after comparison of the proportion of beer fermentation. And a specific gravity of a liquid denser than water. The density of water 1 kilogram per liter, and therefore, if the specific gravity of a liquid is 1.06, one liter of 1.06 kg of the weight of the liquid.
Production of liquid is called beer wort. Since the wort with a lot of sugar is dissolved, its specific gravity is always higher than the proportion of water. Wort will add yeast partially dissolved sugar into ethyl alcohol. When the beer is finished, it has become part of the sugar alcohol (alcohol is less than the density of water, 0.79 kg / liter), so its gravity is always less than the proportion of pre-fermentation.
Glucose is the main sugar into alcohol. Many reactions take place inside the yeast that ultimately each molecule of glucose into two molecules of ethyl alcohol and two carbon dioxide molecules.
According to the periodic table can be calculated molecular weight of these two molecules. Common molecular weight alcohol is 46.0688, the molecular weight of carbon dioxide is 44.0098. You need two numbers to calculate the alcohol content of beer.
During the fermentation process, most of the carbon dioxide produced by the reaction solution in the form of bubbles to escape, and left the vessel via the ventilation holes. We can say that all the carbon dioxide leaving the fermenter, because of the amount of beer left in the amount of leave is minimal compared.
View the equation, you will find each split into two glucose molecules of ethyl alcohol and two carbon dioxide molecules. That is, whenever there is a molecule of carbon dioxide leaving the fermenter, fermenter to form a common alcohol molecules. By molecular weight calculations, whenever there 44.0098 grams of CO2 leaving the fermenters will form 46.0688 grams of ethyl alcohol. Another way, for each gram of CO2 that bubbles off, it will generate about 1.05 grams of ethyl alcohol.
Comparing the initial and final gravity gravity. If the initial wort specific gravity is 1.06, so the proportion of fermented is 1.02. Subtracted from the initial proportion of the final proportion can be calculated to leave the fermenter CO2 weight. It is equal to 0.04 kg / l. Then multiplied by 1.05, weight of the alcohol in the container. It is equal to 0.042 kg / l. Now that you know the quality of the quality of the solution (1.02 kg / liter) and ethanol (0.042 kg / l), by dividing the two can calculate the percentage of alcohol. Calculated 0.042 / 1.02, equal to 0.041 (4.1%).
Note that, according to the percentage of alcohol is higher than the calculated mass percentage by volume, since the volume of the same amount of alcohol than water. Thus, the percentage of alcohol if you want to calculate the mass will be converted into the percentage of alcohol by volume, simply divided by the density of alcohol. At this time, the percentage of alcohol by volume is the result of 4.1 / 0.79 (5.2%).
In Colorado, the beer sold in grocery stores must be "3.2" low-grade beer. Calculated by mass, low-alcohol beer can not be higher than 3.2%. However, the calculation of liquor stores to sell beer alcohol by volume, most of the alcohol content of beer is about 5%. However, if the weight in terms of volume, you will find "3.2" beer alcohol content by volume of 4%. Although the difference between them is large, but may not think so serious.
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