Fermentation of Wine Yeast
Let me first write about the basic concept of Fermentation, which is to cool the Wort obtained during saccharification to about 20°C, and then pour it into the Waskback fermentation tank. Generally, it is about two-thirds of the height, and then the yeast is added. And mixing, the yeast will eat the sugar in the wort and convert it into alcohol, carbon dioxide and heat. During the process, the wort needs to be slowly stirred to prevent the yeast from dying and stopping operation due to excessive temperature. After more than hours of fermentation, a wine juice with an alcohol content of 6-8% will be obtained, after which it can be distilled for the first time.
The above is the basic principle of fermentation.
However, as the architect Mies Van Der Rohe famously said, "The devil is in the details", the devil is in the details, and fermentation is used as a whisky production process, which is known to definitely affect the key aspects of the flavor of the product, such as a long time. Fermentation, short-term fermentation, the material of the fermentation tank, the type of yeast, the temperature of fermentation, the timing of the yeast, etc., each factor can be said to affect the flavor trend of whiskey, and it can also be said that it affects the distillery. "Winery style."
The type of yeast used in the distillery is mostly Saccharomyces Cerevisiae (scientific name: Saccharomyces Cerevisiae), also known as baker's yeast or brewer's yeast. It is the most common and widely used in daily life. The working temperature is around 20-35°C, the best The growth temperature of the yeast is about 30°C. If the wort temperature is too low, the yeast will enter a dormant state and stop working. If the temperature is too high, the yeast will die. When the yeast is working, in addition to alcohol, it will also produce Carbon dioxide and heat.
Therefore, the purpose of most distillers to cool down the wort to about 20°C should be to keep the wort temperature from reaching 35°C or above too quickly during fermentation, so as to avoid the death of the yeast due to too high temperature and making the fermentation time too early Stop; and the distillery will properly stir and cool the fermentation tank, and at the same time make the mixing of wort and yeast more balanced, it can also reduce the excessive accumulation of bubbles generated in the fermentation tank, so that the wort will not overflow due to excessive swelling Outside the barrel.
Many distiller’s fermentation tanks have a cover. Some say it is to prevent the wort from overflowing or to prevent foreign matter from entering, but it is also said to reduce the temperature loss of the fermentation tank. The weather is not as expected. Scotland has four distinct seasons. The temperature difference between winter and summer can reach more than 20 degrees. The temperature during fermentation is of course not the same. Traditional fermentation tanks made of Oregon Pine or Larch still need to use lids to prevent cold air outside. Enter to minimize the impact of temperature loss on the efficiency, quality and flavor of fermentation.
The more modern stainless steel fermentation tank, in addition to the advantages of easy cleaning and maintenance, can also install a temperature control device inside the fermentation tank to ensure stable temperature and make the fermentation process more efficient; but why is it so convenient? For stainless steel fermentation tanks, there are many distilleries, such as the Yamazaki and Yoichi distilleries in Japan, or the distilleries of the Diageo Group. They still insist on keeping the ones that are difficult to clean, troublesome, and have no temperature control. What about wooden fermentation tanks?
And a paragraph from Yamazaki Yamazaki Distillery, the brief description of the two fermentation tanks in the distillery seems to reveal a little clue, the abstract is as follows: "Stainless steel fermentation tanks help temperature control, and can produce a cleaner, elegant aroma ; Wooden fermentation tanks are more complicated to control temperature and require careful maintenance, but thanks to the influence of active lactic acid bacteria and other microorganisms, they can produce a more complex and profound taste."
It’s better to re-recognize the protagonist of "Yeast"; as mentioned above.
During the fermentation process, yeast will convert the sugar in the wort into ethanol (alcohol), heat and carbon dioxide (gas). However, The three products produced by yeast, the ethanol (when the alcohol concentration exceeds about 6-8%) and heat (the temperature exceeds about 35°C) will kill the yeast itself. The heat can be controlled by artificial means, but it does not stop. The increased alcohol concentration can only be solved by yeast.
Yeast converts alcohol into "esters" in an attempt to dilute and reduce the alcohol concentration to increase living space, but in the process of struggling, many yeast members die and automatically break down into smaller sugars, amino acids, fatty acids and glycerol. Many different substances, and become the long-latent "active lactic acid grains" food, lactic acid grains gradually increase and multiply; and these fine grains and microorganisms generally come from germinated barley and remain in wort, or wood Among the wood of the fermentation tank.
When the number of these active lactic acid pans and microorganisms slowly increases, they will start to snatch the nutrients in the wort with the yeast. The lactic acid pans will also produce ethyl lactate, and the yeast will produce acetic acid to resist. The acetic acid in the acetic acid, Then the esters produced with alcohol (ethanol) and lactic acid gall will produce ethyl acetate with a floral and fruity aroma after the esterification reaction. Knowing that it is because of the lactic acid gall that makes the taste more complex and changeable).
According to a series of experimental reports found on the Internet, the content of active lactic acid in the wort rose rapidly after the fermentation began to 40 hours, and indirectly caused the yeast to produce more acid to resist. It can also be understood to some extent from this After a period of time, the aroma of the wort during fermentation began to change significantly, and the time point of "40 hours" is also generally defined as the dividing line between "long fermentation" and "short fermentation", although there is no explicit stipulation. However, most of them also think that 50 hours or more is long, and the following is short.
The timing of adding yeast is also a very interesting place. According to another article described a method called Pre-Fermentation, some distillers will first cool the wort in a fermentation tank and let it stand still. For 24 to 48 hours, let the latent lactic acid grains and microorganisms grow for a period of time, and then put the yeast grains into it, and the aroma of alcohol will be produced. The performance is also significantly different; and in the method of making sourdough bread, there is also one A very similar technique, the bread made in this way has a softer texture and a more obvious sour aroma.
Based on the above information, the author seems to be able to infer that "fermentation" can indeed affect the flavor trend of the liquor, and it can also explain why more malt taste can be felt from the "short fermentation" works, while the "long fermentation" works It has a more complex floral and fruit aroma; however, even though long fermentation can bring more complex aromas to the wine, it is accompanied by the risk of insufficient alcohol due to excessive fermentation, because "yeast" in addition to breaking down sugar, from above The data also shows that as time goes on, the "other substances" in the fermented wort continue to increase, while the sugar content continues to decrease, but the alcohol is still continuously being converted, resulting in insufficient alcohol content in the fermentation broth. The resulting "efficiency" problem.
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