Bitterness is one of the basic senses of taste, and it is a taste perception that makes people's taste cells feel unpleasant. Bitterness is something that people don't appreciate, and it can be reflected in everyday language.
The sensory nerves of bitterness are distributed at the base of the tongue, and the response to bitterness is slower to be transmitted to the brain, and it is not felt until other flavors are lost. Bitterness is an undesirable taste in sake, which is characterized by slow reaction and strong persistence, which does not disappear easily.
Bitterness is a sensation caused by a liquid stimulus that contains chemicals. The receptors of taste are taste buds, which are oval in shape and are mainly composed of taste cells and support cells, and there are microvilli at the top of taste cells that stretch in the direction of taste pores, in contact with saliva, and nerve fibers innervated at the base of the cells. The formation mechanism of taste is as follows: the bitter taste receptor protein distributed on the top microvilli of taste cells in the taste buds is activated after combining with the bitter substances dissolved in the liquid phase, and through intracellular signal transduction, the taste cell membrane is depolarized, and then the postsynaptic excitation of nerve cells is triggered, and the excitatory signal enters the nucleus of the medullary tract along the facial nerve, glossopharyngeal nerve or vagus nerve, replaces neurons to the thalamus, and finally projects to the taste center in the lowest part of the back gyrus of the brain, and finally produces bitter taste perception through the integration of the nerve center. The taste threshold of bitterness is generally smaller, and the taste perception is more sensitive. See Table 1.
Please look at the fireworks The bitter taste is the same as the stinky smell in liquor, and it is not welcome. However, in some foods, it must have a certain bitter taste, such as cigarettes, tea, beer, wine, rice wine, coffee, chocolate, etc. If there is no bitterness, these foods will be off-grain, affecting their unique flavor. Generally speaking, bitterness has 3 characteristics:1After long-term consumption of bitter food, consumers will get used to it for a long time, and the feeling of bitterness will be dull, and over time, it will not feel bitter, such as drinking beer, which feels very bitter at first, and the bitterness is greatly reduced over time, and even does not feel bitter; 2.The bitter reaction is slow, and there is a strong persistence, not easy to disappear, so it often makes people unhappy, such as when evaluating wine, it is said that the wine has anti-bitterness rather than former bitterness, which is the reason, when the other flavors have disappeared, the bitterness still exists, and the feeling is more prominent; 3.I dare not say that bitterness is addictive, but it can be said with certainty that addiction contains bitterness, such as tobacco (including opium smoke), wine, tea, coffee, cocoa, etc., all of which can be addictive and contain bitterness. According to our experience, there are two types of suffering: one is persistent suffering, which lasts for a long time and disappears very slowly, like a decoction, which people don't like; Another, such as high-quality beer and tea, has a strong bitter taste at the beginning, but disappears quickly, that is, instantaneous bitterness, which makes people feel refreshing, and people like it instead (many famous sauce-flavored liquors have the characteristics of instantaneous bitterness).
The bitterness is not static, and when acid is added to the bitterness, the bitterness of the wine increases (multiplication); Adding sugar to the bitterness reduces the bitterness (killing effect), and this method is commonly used in the blending and flavoring of baijiu to select different types of base liquor for combination, skillfully diluting or covering up the defects of baijiu's bitterness.
1 Bitter substances in liquor
According to the analysis and evaluation of the bitter substances in liquor, there are mainly the following categories:
1.1 furfural
Furfural is the main furan system component in liquor, which is generated by microorganisms in the rice husk and raw material husks. Furfural is one of the important components of "bad aroma" or "burnt aroma" in wine, but excessive furfural will cause a burnt bitter taste in wine.
1.2 Higher alcohols
Higher alcohols are a class of alcohol-soluble substances with high boiling points, referring to monovalent alcohols with more than three carbons, and the main alcohols in wine are n-butanol, isobutanol, n-propanol, isoamyl alcohol, etc., and the mixture of these higher alcohols is what we usually call fusel oil. The main way of producing higher alcohols in wine is that during the fermentation process, the protein in the raw material is hydrolyzed into amino acids in the new brewing platform, and the amino acids are deamination and carbon dioxide through the Ili reaction to form higher alcohols with one carbon less than amino acids. High-grade alcohol is an important flavor component in the wine, but after the content is too high, it will bring bitterness to the wine, among which n-butanol has a small bitterness, n-propanol has a heavy bitterness, isobutanol has a very strong bitterness, and isoamyl alcohol is slightly sweet and bitter.
1.3 Tyrosol
Tyrosol, also known as p-hydroxyphenyl ethanol, is one of the main dialcohols in liquor, although its aroma is very soft, but the bitterness is heavy and long, under normal circumstances, liquor contains 0 parts per 10,0005 of tyrosol will have a bitter taste when tasting. The production of tyrosol is mainly produced by excessive yeast acting on tyrosine, therefore, using too much koji will lead to the production of excessive tyrosol, which makes the wine bitter, which is also the root cause of the bitterness of koji wine.
1.4 Acrolein
Acrolein is easy to produce when the hygienic management of liquor fermentation is poor and the fermentation is abnormal, it is generated by yeast and lactic acid bacteria acting on glycerol during the fermentation process of liquor, so it is also known as glyceraldehyde. Acrolein not only has a spicy pungent odor, but also has a great persistent bitter taste.
1.5 Other substances
There are many bitter components in liquor, and some phenolic compounds, furan compounds, and pyrazine compounds decomposed from tannins in raw materials also often have a bitter and astringent taste; Some soluble inorganic ions, such as magnesium ions, sulfate ions, etc., will bring a certain bitterness to the wine.
2 Analysis of the causes of the bitter taste of liquor
2.1 Raw material reasons
Grain is the meat of wine, in the brewing process of Chinese liquor, grain is the most basic raw material, and the quality of grain is the basis for determining the quality of liquor. In the liquor industry, there is a saying that "sorghum produces wine aroma, corn produces wine sweetness, wheat produces wine roughness, rice produces wine purity, and barley produces wine punch", which shows that different grains have different effects on wine quality. The improper selection and use of grain may bring bitterness to the wine and affect the quality of the wine.
Generally, the requirements for liquor raw materials are full of particles, high starch content, moderate content of other components, low moisture content, no rot, mold, germination, insect moth, etc., and it is best to use new grains.
The use of moldy, rotten grains as raw materials for brewing, the moldy bitterness in the raw materials and the bitter substances produced by decay will be brought into the wine, and the wine body is not only bitter, but also has a strong odor.
The impurities of the grain contain some soluble inorganic ions with bitter taste, and the use of sorghum with too high impurity content as the raw material for brewing will bring the bitter substances in the impurities into the wine, causing the wine to be bitter.
The starch content of aged grains is lower than that of new grains, and a large number of impurities are mixed in during storage, which can cause bitterness when introduced into the wine.
2.1.1 sorghum.
Sorghum husks contain about 2% tannins, which are cooked and fermented to produce phenolic compounds such as vanillic acid, which can give the wine a special aroma, which is one of the reasons for the aroma of sorghum. However, if the tannin content is too high, it is easy to be carried into the wine, which will give the wine a bitter and astringent taste. Sorghum can be divided into japonica sorghum and glutinous sorghum according to starch types, japonica sorghum mainly contains amylose, which is not easy to gelatinize, easy to age, and has few enzyme action points; However, the glutinous sorghum new brewing platform mainly contains amylopectin, which is easy to gelatinize, has strong water absorption, and has many enzyme action points. Therefore, under the same process, the quality of the wine made by using glutinous sorghum as the raw material for brewing is better than that of japonica sorghum.
Tannins are bitter: Sorghum contains about 2% tannins, and the tannins themselves have a bitter and astringent taste, and excessive tannins are easy to be carried into the wine, making the wine present a bitter and astringent taste.
Japonica sorghum: Japonica sorghum mainly contains amylose, and the number and variety of aromatic and flavorful substances produced during the fermentation process are insufficient, resulting in the uncoordinated balance of esters in the original liquor, which is easy to bring bitterness, especially when the total acid in the wine is insufficient, the bitterness of the tannins is poorly concealed.
2.1.2 corn.
There are a total of yellow corn, white corn, waxy corn, japonica corn, etc. Generally, the starch content of yellow corn is higher than that of white corn, and japonica corn mainly contains amylose, which is not easy to gelatinize, easy to age, and has few enzyme action points. Waxy corn mainly contains amylopectin, which is easy to gelatinize, has strong water absorption, and has many enzyme action points. Therefore, under the same process, the wine quality of waxy corn used as the raw material for brewing is better than that of japonica corn. Corn contains more phytic acid, which can be fermented to produce cyclohexanol and phosphoric acid, phosphoric acid can promote the formation of glycerol, and cyclohexanol and glycerol can give wine a mellow sweetness.
Use ungermized corn: Corn germ contains a lot of fat, which is easily oxidized to higher alcohols (fusel oils), which give the wine a bitter taste. Therefore, when using corn as the main raw material for brewing, it is recommended to remove the germ.
2.1.3 rice.
Rice is the seed of rice and is one of the main crops in southern China. Rice is divided into indica, japonica and glutinous rice. Rice has a high starch content, so using rice as a raw material for sake brewing has a relatively high yield, relatively low protein and fat content, no tannins, and almost no peculiar flavors. The starch structure of japonica rice is loose, which is conducive to cooking and gelatinization; Glutinous rice is soft and has a high viscosity after cooking, so glutinous rice is generally not used as a raw material for sake brewing alone, but is used in combination with other grains.
Improper cooking of rice: If the cooking is improper, the japonica rice is too sticky, which will lead to excessive fermentation and heating, so that the wine will bring bitter substances into the wine, causing the wine to be bitter, so the general japonica rice will choose to use semi-solid or liquid process for brewing, of course, you can also increase the use of auxiliary materials, but this will destroy the refreshing feeling of rice.
2.1.4 Wheat.
In addition to starch, there are also a small amount of carbohydrates such as sucrose, glucose, fructose, etc., and the protein components of wheat are mainly gluten and glutenin, and gluten is mainly amino acids, and these proteins will form substances that give the wine a special flavor during the fermentation process. However, if fermentation is not done properly, the protein is broken down into tyrosine, which is very easily broken down into tyrosol, causing the wine to be bitter.
Bitter wheat protein: When the amount of koji is large, the excess yeast will break down the tyrosine decomposed from the protein into tyrosol, causing the wine to be bitter.
Bacterial infection: Although the amino acids decomposed into proteins are nutrients for wine-making microorganisms, excessive amino acids can also cause miscellaneous bacterial infections and produce various bitter substances.
2.2 Excipient reasons
Common auxiliary materials for liquor production include bran, grain bran, sorghum husk, coarse rice husk, corn cob, etc. Brewing solid-state process liquor often uses coarse rice husk as an auxiliary material for liquor, which is an ideal filler for solid-state liquor, and the appropriate addition of coarse rice husk can adjust the acidity, starch concentration and fluffiness of the dregs, so that the fermentation is normal, and it does not collapse during distillation, so we need to choose coarse rice husk when choosing rice husk.
Rice husk contains pectin, which will produce harmful substances methanol during fermentation, and rice husk also contains polypentose, which is easy to form furfural during the fermentation process, resulting in wine bitterness. Therefore, the rice husk needs to be steamed during use to remove the pectin and polypentose.
Bran husk thickness: The bran husk is crushed too finely, which makes the dregs greasy, easy to cause abnormal heating during the fermentation process, and the fermentation speed is fast, which is easy to produce excessive fusel oil, making the wine bitter.
Quality requirements: The quality and dosage are related to the quality and yield of liquor products, and the coarse rice husk is required to have good water absorption, less impurity content and no mildew. Aged bran and mildewed coarse rice husks will cause wine bitterness.
2.3 Causes of badness
2.3.1 The role of the bad.
The main function of the grains in the wine is to reduce the concentration of starch in the cellar, slow down the fermentation rate, keep the grains with a certain moisture, improve the aroma of the grains, and appropriately increase the yield of the liquor. And because the grains themselves have a certain acidity, the acidity of the grains in the cellar can be controlled, which can play a certain role in inhibiting the growth of miscellaneous bacteria.
2.3.2 Use of the damp.
The use of dregs should pay attention to no mildew, appropriate moisture, appropriate acidity, and appropriate proportion.
The amount of dregs used is too small, the starch concentration is too high, and the fermentation temperature is high, which prevents the normal fermentation and is easy to produce excessive fusel oil, which makes the wine bitter. The amount of dregs is too large, the acidity is large, the fermentation is slow, the temperature cannot rise normally, and the workload is large, the enzyme consumption is large, and the dregs will also be bitter. The use of moldy grains will cause the wine to have a moldy and bitter taste.
2.4 Causes of koji
Koji contains a large number of enzymes and microbial communities, which mainly play the role of saccharification and fermentation, so it is also called saccharification starter culture. Koji is mainly divided into large koji, small koji and bran koji, and some workshops directly use saccharification enzymes and yeast instead of koji for saccharification and fermentation.
Daqu is rich in various enzymes such as saccharification enzymes, amylases, esterases, and proteases secreted by bacteria and molds; Brewing microorganisms mainly include alcoholic yeast, ester-producing yeast, various acid-producing bacteria, etc., and in addition to producing ethanol during the fermentation process, it can also produce aromatic and flavorful substances that enrich the liquor body.
The enzymes and microorganisms in koji and bran koji are mainly saccharifying enzymes secreted by Rhizopus and alcoholic yeast, Aspergillus and Rhizopus.
The main enzymes and brewing microorganisms in raw koji are raw starch saccharification enzyme and alcoholic yeast, which have strong liquor production ability, but the aroma production ability is even weaker than that of small koji and bran koji.
The direct use of saccharification enzyme and yeast as saccharification starter agent, although the wine yield is high, but the aroma production ability is very poor, and because of its short fermentation time, strong fermentation, high fusel oil content, the wine quality is bitter.
Koji is bitter: whether it is large koji, small koji, bran koji or raw koji, in the process of use, you must pay attention to the amount of koji, if the amount of koji is too large, the excess yeast will decompose the protein into tyrosol, making the wine bitter.
2.5 Process reasons
2.5.1 Solid-state fermentation.
The traditional solid-state koji process is mainly composed of five types of processes: gelatinization process, saccharification process, fermentation process, distillation process and storage blending process.
The cellar temperature is too high: the temperature of the lees in the pool is too high, the heating rate is fast, and the yeast autolyzes more, which produces a large amount of high-grade alcohol, which makes the wine bitter.
Poor sealing: Poor sealing of fermentation, a large amount of air enters, causing distiller's grains to be infected with miscellaneous bacteria, generating a large number of miscellaneous substances, making the wine bitter.
Site hygiene: If the fermentation site is not cleaned in time, the distiller's grains will be infected, and a large number of peculiar odor substances will be generated, which will be distilled with the liquor, making the finished liquor bitter.
Excessive distillation fire: When steaming the wine, the fire is not properly controlled, and the fire is too large, and the fusel oil with a high boiling point is steamed into the wine, making the wine bitter.
Improper wine picking: fusel oil is a high boiling point alcohol-soluble substance, mainly existing in the head and tail of the wine, do not pinch the head of the wine or pinch the head too little, the tail is too late, will make the content of fusel oil in the wine high, resulting in bitterness of the wine.
2.5.2 Liquid fermentation.
Raw cooking wine adopts the process of liquid fermentation and liquid distillation, and there are only three major processes of fermentation, distillation and storage blending, and its brewing process is very simple.
Fermentation management: During the fermentation process of raw cooking wine, the fermented mash needs to be stirred to ensure the full contact between the grain and the winemaking microorganisms and enzymes. However, if you do not pay attention to cleanliness and hygiene during the mixing process, it will bring miscellaneous bacteria into the fermented mash, causing the wine to be bitter. Similarly, poor sealing can also cause bacterial infections that can make the wine bitter.
Excessive distillation fire: When steaming the wine, the fire is not properly controlled, and the fire is too large, and the fusel oil with a high boiling point is steamed into the wine, making the wine bitter.
Improper wine picking: fusel oil is a high boiling point alcohol-soluble substance, mainly existing in the head and tail of the wine, do not pinch the head of the wine or pinch the head too little, the tail is too late, will make the content of fusel oil in the wine high, resulting in bitterness of the wine.
2.6. Storage containers and transportation equipment
After the original liquor is distilled, it needs to be stored to achieve a balanced and harmonious body. The cleanliness of storage and conveying equipment will also affect the quality of liquor.
Now the common storage containers on the market are pottery jars, stainless steel tanks, blood containers, cement pools, etc., and the transportation pipeline should use stainless steel pipes or stainless steel hoses made of food-grade stainless steel, if you use pipes containing other metal materials, such as iron pipes, aluminum pipes, hoses, etc. The first is that the pipeline is easy to rust, the second is that it is easy to bring strange odors to the wine, and the third is that if it contains magnesium ions, it will cause bitterness if dissolved in the wine.
If the storage container is left empty for a long time, it is easy to cause mold infection and bring bitterness to the sake when the container is filled with sake next time.
3 How to prevent the bitterness of liquor
3.1. Strengthen the steaming treatment of excipients
Strengthen the steaming of excipients to eliminate their evil odors. When steaming, the fire should be large, the time should be enough, after the steaming is completed, it should be dried in time, and the pile should be bagged for later use. Brewing raw materials that have moldy growth should also be steamed before use.
3.2 Proper ingredients
In order to ensure the normal progress of saccharification and fermentation, it is necessary to use the appropriate amount of koji and the amount of fermented wine. Maintaining a certain amount of protein is good for vigorous fermentation and the flavor of the liquor, but it should not be excessive, such as excessive is very harmful to the liquor. High protein content will inevitably produce more tyrosol, resulting in bitter wine, fusel oil exceeding the standard, and the wine yield will inevitably decrease.
3.3. Control miscellaneous bacteria
It is necessary to do a good job in the environmental sanitation of the workshop and reduce the pollution of miscellaneous bacteria. Low temperature cellaring, low temperature fermentation, and appropriate reduction of acidity are very important for the improvement of the quality of liquor products.
3.4 Master distillation
Only by taking reasonable retorts and distilling slowly can we have a bumper yield and a bumper harvest, and at the same time avoid a large number of bitter substances and dry and spicy substances from entering the wine. In addition, it is necessary to control the degree of wine picking according to the requirements of raw materials and wine quality.
3.5. Strengthen blending
The bitter substances in liquor exist objectively, and the difference is only more and less. Therefore, in addition to strictly grasping the process conditions and reducing the formation of bitter substances, it is also important to apply blending and seasoning technology to improve the quality of liquor. Bitter substances are mostly high boiling point substances, so they are not easy to disappear during storage, but in the case of light bitterness, if the blending and seasoning can be reasonably used to maintain a certain balance of fragrance, in the case of the coordination of aroma substances, there is an appropriate amount of bitter substances, and the bitterness is not prominent.
4 Solutions to the bitterness of liquor
4.1 Filtration method
For liquor with heavy bitterness or heavier, the filtration treatment method can be preferred (it is recommended to use a multi-functional four-effect filter). According to the bitterness, different media can be used to treat the wine, filter out some bitter substances in the wine, and reduce the bitterness in the wine. For example, the use of G-type activated carbon can filter fusel oil and aldehydes in the wine, so as to achieve the purpose of reducing the bitterness.
4.2 Hook method
There are two main ways to deal with the bitterness in liquor:
4.2.1 Dilution method.
Liquor with a lighter bitter taste can be diluted. The base liquor with fusel oil and aldehyde content is not high to dilute the wine sample to reduce the concentration of bitter substances in the wine, and when the concentration of bitter substances in the wine is below the bitterness threshold, it can achieve the effect of reducing or eliminating the bitterness in the wine.
4.2.2 Cover-up.
There are generally two modes of blending and seasoning, the first is to use a special process with a heavier sweetness to brew a sweet flavored liquor, which masks the bitterness in the wine through sweetness; The second is that for bitter liquor with low acidity, the bitter taste can be reduced or eliminated by adding raw liquor with high acidity, and the masking effect of hydrogen ions can be achieved.
5 Conclusions
In summary, the content of bitter substances in liquor can be effectively reduced by controlling the quality of raw materials, brewing process, koji dosage, environmental hygiene, blending, etc. Therefore, in the whole winemaking process, it is necessary to do all kinds of checks and strict requirements.