Difference+Between+Distilling+and+Fermenting

Difference Between Distilling and Fermenting

Brewing is making of beer by mixing a starch source in water and then fermenting with yeast. There is fermenting and there is distilling. Fermenting is converting carbohydrates to alcohols and carbon dioxide using yeasts. Fermenting in a more simple way is the conversion of sugar into ethanol which has taken place since the 6th millennium and historians found evidence of it starting in ancient Egypt.

Distilling is a separating of mixtures by vaporizing in a boiling mixture. Distilling is a unit operation which involves bringing a physical change such as separation evaporation, filtration or crystallization. Distilled beverages are bottled with sugar such as Grand Marnier or American Schnapps and are called liqueurs.

__**Distilling**__

The beer is brought into a pot still, made of copper, and of a size, according to the dimensions of the distillery. The first still, which is called the beer still, is usually double, that is, there are two of them, and between them is placed another still for the purposes of finishing the operation. The beer stills are provided with scrapers or chains which are dragged constantly over the bottom so that any solid matter from the remaining solid contents in the beer may not adhere to the bottom of the still and be burned. The stills are heated by open fire. In some instances, steam coils are also found in the stills. The shape of the still is said to have a great deal of effect upon the quality of the beer. The stills with big bellies and with rather long arm necks are preferred. The product of distillation from the beer still is known to contain less than 50 percent by volume of the whole mass. The distillation from the beer still is continued until the alcoholic proof of the distillate is too low to be placed in the low-wine tank. The residuary alcohol is then distilled and added to the next distillate. After the alcohol is all distilled the residue left in the still is called spent beer. It is usually disposed of later. It is used, although not very extensively. Instead of selling it for cattle it is sometimes run into tanks sunk into the earth until all the solid matter settles. In some distilleries it is put into tanks and destroyed by bacterial action. The low wines, after they are collected from the beer stills, are put into a whisky still, which is smaller than the beer stills, and subjected to a second distillation for the purpose of bringing them to an alcoholic strength suitable for bonding, namely: full 50 percent alcohol. When the distillate from the whisky still becomes too weak to be used for whisky, it is separated and used again with the beer in the next distillation. After all the alcohol is extracted the residue in the whisky still is known as lees, and the lees are disposed of like the spent beer above described. The spirit, after having been thus secured, is stored in oak casks. Those casks are valuable and are most highly prized. Such casks bring from $12 to $15 each.

The reference is from chestofbooks.com

__**Fermentation**__

Fermentation is the process by which yeast converts the glucose in the wort to ethyl alcohol  and carbon dioxide gas, giving the beer both its taste and its carbonation. To begin the fermentation process, the cooled wort is transferred into a fermentation vessel to which the yeast has already been added. If the beer being made is an ale, the wort will be maintained at a constant temperature of 68 F (20 C) for about two weeks. If the beer is a lager, the temperature will be maintained at 48 F (9 C) for about six weeks. Since fermentation produces a substantial amount of heat, the tanks must be cooled constantly to maintain the proper temperature. These fermentation tanks hold more than 2,400 gallons (9,085 L), which means that it takes four batches of wort to fill one tank. Since fermentation takes at least two weeks, the capacity of the brewery is limited by how many tanks they have. When the wort is first added to the yeast, the specific gravity of the mixture is measured. Later, the specific gravity may be measured again to determine how much alcohol is in the beer, and to know when to stop the fermentation.

When the yeast first hits the wort, concentrations of glucose (C6H12O6) are very high, so through diffusion, glucose enters the yeast (in fact, it keeps entering the yeast as long as there is glucose in the solution). As each glucose molecule enters the yeast, it is broken down in a 10-step process called glycolysis. The product of glycolysis is two three-carbon sugars, called pyruvates, and some ATP (adenosine triphosphate), which supplies energy to the yeast and allows it to multiply. The two pyruvates are then converted by the yeast into carbon dioxide (CO2) and ethanol (CH3CH2OH, which is the alcohol in beer).
 * How Yeast Makes Alcohol and Carbon Dioxide

The fermenter is sealed off from the air except for a long narrow vent pipe, which allows carbon dioxide to escape from the fermenter. Since there is a constant flow of CO2 through the pipe, outside air is prevented from entering the fermenter, which reduces the threat of contamination by stray yeasts. When fermentation is nearly complete, most of the yeast will settle to the bottom of the fermenter. The bottom of the fermenter is cone shaped, which makes it easy to capture and remove the yeast, which is saved and used in the next batch of beer. The yeast can be reused a number of times before it needs to be replaced. It is replaced when it has mutated and produces a different taste -- remember, commercial brewing is all about consistency. While fermentation is still happening, and when the specific gravity has reached a predetermined level, the carbon dioxide vent tube is capped. Now the vessel is sealed; so as fermentation continues, pressure builds as CO2 continues to be produced. This is how the beer gets most of its carbonation, and the rest will be added manually later in the process. From this point on, the beer will remain under pressure. Later the beer is placed in a bottle and it will be under pressure for a short time. When fermentation has finished, the beer is cooled to about 32 F or 0 degrees celsius. This helps the remaining yeast settle to the bottom of the fermenter, along with other undesirable proteins that come out of solution at this lower temperature. Now that most of the solids have settled to the bottom, the beer is slowly pumped from the fermenter and filtered to remove any remaining solids. From the filter, the beer goes into another tank, called a bright beer tank. This is its last stop before bottling or the level of carbon dioxide is adjusted by bubbling a little extra CO2 into the beer through a porous stone

The reference is how stuff works by Karim Nice at chesotbooks .com