Basic properties of higher alcohols
The presence of an appropriate amount of high-grade alcohol in beer can make the wine plump and the aroma coordinate, but if the content is too high, in addition to the obvious difference in taste when drinking, it can also lead to dizziness and headache after drinking, which is commonly known as "above." The main senior alcohols in beer are isoamyl alcohol, isobutanol, and n-propanol, in which the main substance causing the upper part is "isoamyl alcohol", whose normal content in beer is 60-90 mg / L, and the taste threshold is 55 mg / L. L.
Higher-grade alcohol production pathways
There are two main ways: First, the degradation of amino acids to form corresponding alcohols; The second is an advanced alcohol formed by by-products produced by the synthesis of amino acids by sugars. Both use α-keto acid as an intermediate, keto acid decarboxylates to form aldehydes, and aldehydes are reduced to alcohols.
III. Main factors influencing the production of advanced alcohols
1. Effects of strains
Different yeast species produce higher alcohol content under the same conditions.
2. Effect of yeast inoculation volume and multiplier
It is generally believed that the addition of yeast is small, and the yeast produced after the proliferation of yeast is conducive to the production of higher alcohols, and the increase of yeast addition is conducive to the reduction of the content of higher alcohols. At present, most production companies have control of the number of leavened mother cells in full cans: 18 ± 2 × 106 / mL, and the peak yeast number control is 50-70 × 106 / mL. If it is low, the amount of yeast added should be increased appropriately.
3. Effect of α-N in wort
The α-N content in wheatale should be maintained in a reasonable range. Excessive or low levels will lead to an increase in the content of advanced alcohols. When the α-N content in wheatale is low, yeast can form amino acids through synthetic pathways. In this process, due to the lack of N sources, yeast synthesizes more ketoacids to form more advanced alcohols; If the amino acid content in the juice is too high, yeast can form a higher alcohol with one less C atom than the original by decarboxylation. In general, the α-N content of 11-12 ° P wort is more appropriate to control between 170-190 mg / L, otherwise appropriate adjustments should be made to the saccharification process or formula.
4. Effect of Oxygen Inhalation in Wheat Juice
The content of wort juice is closely related to the proliferation of yeast. If there is insufficient oxygen, yeast proliferation is slow, and it is easy to contaminate miscellaneous bacteria, which affects normal fermentation. However, if there is an excess of oxygen and rapid proliferation of yeast, the N available in wort will be consumed in a short period of time, which will easily cause a lack of yeast nutrient salts, and the content of advanced alcohols will increase. The control range is generally required to be 8-10 mg / L. For non-wheat-juice oxygen-filled measuring equipment manufacturers, the control of oxygen filling can also be based on experience through the control of oxygen filling pressure and oxygen filling time. The normal oxygenated pressure is controlled at 0.2 MPa, and it can be seen from the Wencuili tube mirror that the wort is oxygenated and foamed. At the same time, if there is too much oxygen, the rapid proliferation of yeast will also lead to the "overflow tank" phenomenon in the early stage of fermentation, which will not only cause waste of spilled Wort, but also lead to microbial pollution.
5. Effects of Fermentation Conditions
When the fermentation temperature is high, more advanced alcohols are produced. Since advanced alcohols are mainly produced during the fermentation of yeast, that is, the first 3 days of the main yeast, the temperature of the wheat juice inoculation during production should not be too high(finally &;; Lt; 8 °C), main leaven temperature & amp; Lt; 12 °C to reduce the production of advanced alcohols. In order to shorten the fermentation period, some companies will increase the temperature of inoculation and main leaven in the juice, which will inevitably lead to higher alcohol content in the finished wine.
Fermentation pressure will also have a great impact on the content of higher alcohols. The higher the pressure, the lower the production of higher alcohols. Therefore, some manufacturers in the production use the pressure of 0.10-0 .16 MPa during fermentation, which not only helps to reduce the production of advanced alcohols, but also allows the CO2 produced during the fermentation process to be dissolved into the wine body and excreted during the fermentation process. Mixed taste.
6. Effects of Fermentation
The higher the degree of fermentation, the more vigorous the fermentation, the higher the alcohol produced and the higher the alcohol content. Reasonable fermentation is controlled between 68 % and 70 %.
7. Effect of yeast autolysis
After the main fermentation is over, most of the yeast is deposited at the bottom of the cone. If it is not discharged in a timely manner, it can easily cause yeast to self-dissolve, leading to the precipitation of alkaline amino acids, which increases the PH of beer, resulting in an increase in the content of advanced alcohols. At present, the yeast recycling process used by most manufacturers is to increase the pressure 72-120h to start recycling yeast, but some manufacturers begin to recycle yeast when the fermentation liquid cools or drops, which can easily lead to high alcohol content. The yeast recovery time can be advanced to the increase pressure and the recovery of yeast can be completed within 72-96h of the increase pressure.
In addition, reducing the use of algebra of yeast can also increase yeast activity and reduce the occurrence of yeast autolysis. In general, the requirements of ≤ 4 generations should be met.
8. Effect of "alcohol Ester ratio"
In recent years, experts have suggested that the top of beer drinking is not only related to the high alcohol content, but also related to the "alcohol Ester ratio" in beer. For example, the high alcohol content in white wine reaches 1000 mg/L, but it does not have a top after drinking, and when the high alcohol content in beer reaches 90-100 mg/L, there will be a "top" phenomenon after drinking. The reason for this is that the 'alcohol Ester ratio' in white wine is "low, about 4.5:1, and the" alcohol Ester ratio "content in beer is high, about 10:1. Since advanced alcohols stimulate the brain nerves in the blood and shrink them, and esters stretch the brain nerves in the blood, "alcohol esters" are not "above" after drinking.
From the above analysis, it can be seen that the factors that lead to high alcohol content are relatively complex and can not be solved by adopting one or two measures. Different process improvement measures should be adopted according to the actual situation of different factories.