The production of low-grade liquor, there are two major technical problems, that is, "water flavor" and "turbidity", it is difficult to maintain the style of the original wine, through several years of efforts, these two major problems have been solved, and solved better and better. However, with the development of low-grade liquor, the increase in production, it is found that the low-grade liquor storage changes, the taste becomes lighter and has a peculiar smell, with the increase of storage time and the difference in storage conditions, this change is particularly serious. In order to explore the reasons for the quality change of low-grade koji wine in storage and find out the scientific basis for solving the problem, Sichuan Food Fermentation Industry Research and Design Institute, Yibin Wuliangye Distillery, Sichuan Tuopaiqu Distillery and Sichuan Gulinlang Distillery jointly studied the quality changes in the storage process of low-grade koji wine. Changes in the quality of low-grade koji wine during storage are mainly changes in trace components. Using the Japanese Shimadzu GC-TAG gas chromatograph, homemade capillary column, the trace components of the wine are detected. Low boiling point alcohol esters using direct injection, low boiling point organic acids using derived benzyl esterification method, high boiling point alcohol esters using ether - pentane enrichment extraction, a total of 30 kinds of esters, 11 kinds of acids, 24 kinds of alcohols, 5 kinds of aldehydes and ketones, more than 19800 data were obtained. Analyzed every 3 months, combined with sensory tasting, some regular things were found, and the changes in the trace components of reduced wine and low-grade koji wine in storage were initially mastered, and the reasons for the change in taste were understood, which provided a reliable scientific basis for stabilizing and improving the quality of low-grade koji wine.
(1) Analysis of aromatic components in the storage process of low-grade koji wine
1． alcohol content
The alcohol content decreases slightly during storage, but the change is not obvious. After 1 year, the difference between the high is 0.15% (volume fraction), while the difference between the low is only 0.07%. The decrease in the alcohol content of the wine sample during storage is generally due to the loss of volatilization.
2． Organic acids
The types of acids contained in low-grade liquors of 38% to 39% (volume fraction) and 52% to 53% (volume fractions) of reduced alcohols are basically the same. The acid content of strong aromatic liquor (Wuliangye, Tuopai Qujiu) above 10mg/100mL is 3 kinds of acetic acid, caproic acid and lactic acid, and 5 kinds of propionic acid, isobutyric acid, n-valeric acid, heptanoic acid and caprylic acid below 1~10mg/100mL. There are 2 kinds of acetic acid and lactic acid with an acid content of more than 10mg/100mL, and 7 kinds of formic acid, 1~10mg/100mL for formic acid, propionic acid, isobutyric acid, n-butyric acid, isovaleric acid, n-valeric acid and caproic acid, and the content below 1mg/100mL is 2 kinds of heptanoic acid and caprylic acid.
The order in which the various organic acid contents are arranged in the wine sample:
(1) Wuliangye is 39% (volume fraction) of wine-like caproic acid> acetic acid> lactic acid> n-butyric acid> n-valproic acid> formic acid> isovaleric acid> heptanoic acid> isobutyric acid> propionic acid > caprylic acid.
(2) Wuliangye is 52% (volume fraction) of wine-like caproic acid> acetic acid> lactic acid> n-butyric acid> n-valeric acid> formic acid> heptanoic acid> isovaleric acid> isobutyric acid> propionic acid > caprylic acid.
(3) Tuopai koji wine is 38% (volume fraction) of wine-like acetic acid>caprolic acid>> lactic acid> n-butyric acid> formic acid> n-valeric acid> caprylic acid> isovaleric acid> propionic acid> isobutyric acid> heptanoic acid.
(4) Tuopai Qujiu is a 52% (volume fraction) wine sample with a 38% (volume fraction) wine sample.
(5) Lang wine is 39% (volume fraction) of wine-like acetic acid>lactic acid> propionic acid>capranic acid> n-butyric acid> formic acid> n-valeric acid> isobutyric acid> isovaleric acid > heptanoic acid.
(6) The wine sample of Langjiu is 53% (volume fraction) and its arrangement is the same as that of 39% (volume fraction).
The total acid amount of low-grade wine increased slightly more than that of low-grade wine. In aromatic wines, the increase in lactic acid, caproic acid and acetic acid is larger, generally more than 1%. In sauce-flavored wines, acetic acid, lactic acid, n-butyric acid and propionic acid increased by more than 1%. Its acid content generally increases slightly with the extension of storage time, and the acid increase of low-grade wine is slightly higher than that of low-grade wine.
3． Esters
The low boiling point components in the famous low-grade wine were analyzed by the direct injection method of the capillary column (65m×0.32mm) coated with 20% DNP+7% Tween-80 mixed fixing solution, and the high boiling point component in the 10% PEG20M fixative fluid-coated capillary column (61m×0.32mm) was concentrated pretreatment method. There are 33 kinds of common qualitative esters and 30 kinds of quantitative esters. The content of various esters varies considerably. There are 4 kinds of high content of ethyl caproate, ethyl lactate, ethyl acetate, ethyl butyrate, and low content include isobutyl acetate, methyl propionate, amyl butyrate, ethyl benzoate and other trace esters.
The main ester content in Wuliangye, Quanxing Daqu Wine, Tuopai Qu Wine, and Lang Wine are, in order:
Ethyl hexanoate> ethyl lactate> ethyl acetate> ethyl butyrate> ethyl valerate (Wuliangye)
Ethyl hexanoate> ethyl acetate> ethyl lactate> ethyl butyrate> ethyl valerate (Quanxing Daqu wine, Tuopai koji wine)
Ethyl acetate> ethyl lactate> ethyl hexanoate> ethyl butyrate> ethyl valerate (langjiu)
Ethyl heptanoate> Ethyl caprylate> Ethyl palmitate> Ethyl linoleate> Ethyl oleate (Wuliangye)
Ethyl caprylate> ethyl heptanoate> ethyl palmitate>> ethyl linoleate> ethyl oleate (Tuopai koji wine)
Isoamyl caproate> Ethyl palmitate> Linoleic acid acetate> Ethyl oleate (langjiu)
The content size order of the main esters in the above-mentioned famous wines was analyzed once every 3 months, and the analysis was carried out 5 times, and the order of their arrangement remained unchanged.
Low-grade koji wine is stored for a period of time, and its ester is generally reduced. The largest variation is in the low boiling point esters. In the low boiling point ester, the esters such as ethyl caproate vary greatly, and the esters such as ethyl acetate and ethyl butyrate change little. This may be one of the reasons for the "weak taste" of low-grade koji wine after storage.
During the storage process of low-grade koji wine, its high boiling point esters (such as ethyl enanthate, ethyl caprylate, ethyl palmitate, etc.) have little change, but the overall trend is slightly decreasing.
4． alcohols
The analysis of alcohols also uses the same method and column as esters, and a total of 24 alcohols in the famous wine are quantified. The content of these alcohols in high and low koji wines varies greatly. In particular, the content of n-propanol in lang wine reaches more than 130mg/100mL, and if it is highly langjiu, it reaches more than 210mg/100mL.
The large content is isoamyl alcohol, isobutanol, n-propanol, etc., and the small is a high boiling point alcohol, such as heptanol, cyclohexanol and the like. Through post-storage analysis, the content of alcohol in famous wines is in the order of:
Isoamyl alcohol>-n-propanol> isobutanol> sec-butanol> n-butanol (Wuliangye)
Isoamyl alcohol> n-propanol> isobutanol> n-butanol> sec-butanol (Tuopai koji wine)
n-propanol> isoamyl alcohol> n-butanol> sec-butanol> isobutanol (lang wine)
After a period of storage, the alcohol of low-grade koji wine generally shows a slight upward trend, but the overall change is not large. The low boiling point alcohol class rises slightly more significantly than the high boiling point alcohol class. The largest changes are in alcohols such as isoamyl alcohol and n-propanol. The smaller variation is in high boiling point alcohols.
5． Acetaldehyde, acetal and diacetyl
Whether it is a reduced koji wine or a low-grade koji wine, after storage, the acetaldehyde content decreases, that is, with the increase of storage time, the acetaldehyde content decreases. This is due to the low boiling point of acetaldehyde (21.5 °C) and the easy volatilization of acetaldehyde during storage. In addition, during storage, acetaldehyde may also be reduced to form ethanol; the formation of acetal and diacetyl also consumes a small amount of acetaldehyde. For example, Wuliangye with a wine content of 39% vol is stored for 1 year, the acetal content increases from 16.9mg/100mL to 17.46mg/100mL, and the 38% vol Tuopai qujiu increases from 16.06mg100mL to 16.81mg/100mL.
For example, the content of biacetyl decreased slightly with the extension of storage time, but there was little change, for example, the content of biacetyl decreased from 5.64mg/100mL to 5.30mg/l00mL after 1 year of storage.
Diacetyl is formed by the reaction of acetaldehyde and acetic acid:
CH3CHO+CH3COOH→←CH3COCOCH3+H2O
Diacetyl acetyl acetate water
Due to the prolonged storage period, the acetaldehyde content is reduced, according to the chemical equilibrium law, the chemical equilibrium moves to the left, the acetic acid content increases, and the corresponding double acetyl content should also be reduced. In addition, during the storage process, a very small amount of diacetyl may be reduced to produce vinegar (unitary), and the boiling point of diacetyl is not high (boiling point 87 ° C) and volatilize, these reasons are consumed by biacetyl and its content is reduced.
(2) The effect of changes in aromatic composition on wine obscurity
1． Sensory tasting of koji wines at different storage periods
In order to understand the changes in the taste of koji wine during different storage periods, while sampling and detecting trace ingredients, that is, sampling every 3 months for sensory evaluation.
Judging from the tasting results, as long as the reduced wine (bottle) is well sealed, there is basically no major change in the taste of 1 year of storage; even if the low-grade wine is better sealed, there will be different degrees of unpleasant taste after storage, and as the storage time increases, this taste will be aggravated, and the wine taste will also become lighter, which is due to the change in the ratio of trace components in the wine, which is consistent with the test results.
2． Effect of organic acid changes on the flavor of wine
Judging from the chromatographic detection results, most of the organic acids of reduced and low-grade koji wines showed an increasing trend in the storage process. In the aromatic koji wine, lactic acid and caproic acid increased greatly, followed by acetic acid and butyric acid; in the sauce-flavored koji wine, acetic acid, lactic acid, n-butyric acid, and propionic acid increased more. "Oxidation" and "hydrolysis" reactions are pathways for increased organic acids in the storage of low-grade koji wine. Low-grade wine increases more than low-grade wine, which is an important factor causing changes in taste.
The level of organic acid content is a sign of the quality of wine. In a certain proportion range, wine with high acid content is of good quality; conversely, the quality of wine is poor. Bottled wine, originally at the factory has been blended, trace components balanced, harmonious, but after storage, due to the increase in organic acids in the wine, so that the wine in the acid, ester and other trace components of the balance relationship destroyed, out of balance, causing changes in wine quality.
3. The effect of ester changes on the flavor of wine
After the storage of reduced and low-grade wines, the ester content is generally reduced, which is contrary to the storage results of the original alcohol (high-grade wine). This is a new discovery, and as storage times increase, so does the decrease in ester content. Among the low boiling point esters, ethyl caproate and ethyl lactate and other esters have large changes, and the changes in high boiling point esters are small, but they show a downward trend.
From the chromatographic detection data, taking Wuliangye as an example, the total amount of low boiling point esters, 39% (volume fraction) of the wine decreased from 447.17mg/100mL to 417.58mg/100mL; 52% (volume fraction) of the wine decreased from 549.40mg/100mL to 466.05mg/100mL; The 38% (volume fraction) of Tuopai Koji wine decreased from 307.76 mg/100 mL to 215.70 mg/100 mL, and the 52% (volume fraction) decreased from 462.64 mg/100 mL to 427.70 mg/100 mL. The decrease in total ester is closely related to the type and content of esters in the original wine (before storage). The decrease in low-grade liquor esters of the sauce type was even greater, and the low boiling point esters of 39% (volume fraction) decreased from 466.05mg/100mL to 375.05mg/100mL, which was reduced by nearly 100mg/100mL. For 53% (volume fraction) of langjiu, the total ester is only reduced by about 50mg/100mL. It can be seen that in general, the reduction rate of low boiling point esters in the storage of low-grade koji wine is faster than that of reduced alcohol or high-grade wine. The decrease in esters, the increase in acids, and the imbalance in the proportion of esters are the main reasons for the loss of taste and unpleasant odor after storage of low-grade koji wine.
Esters have the following equilibrium relationship in koji wine:
RCOOR'(ester)+H2O←→R'OH(alcohol)+RCOOH(acid)
This reaction is reversible, when the ethanol content in the wine is high, the acid content is also sufficient, and the reaction tends to esterify. However, when the original wine degree is reduced, especially after the low alcohol, the ester and acid content in the wine is reduced (compared with the original wine or high wine), and the ethanol content is also reduced. The proportion of water increases a lot, prompting the hydrolysis of esters, resulting in a decrease in ester content and an increase in acid content. Of course, this reaction is very slow, and after more than 1 year of follow-up detection, this reaction does exist. The physicochemical mechanism of esterification and hydrolysis in wine is very complex, and how to prevent or minimize this hydrolysis reaction is an important measure to maintain the quality of low-grade koji wine. Further exploration is to be made in the future.
4． The effect of alcohol changes on the flavor of wine
After a period of storage, the alcohols of low-grade wine and reduced alcohol generally show an upward trend, which is consistent with the hydrolysis reaction formula, but the overall change is not as large as that of acids and esters. The increase of alcohols, especially the increase of alcohols such as isoamyl alcohol and n-propanol, coupled with the imbalance of acid and ester, leads to unpleasant odors in wine.
5． Effect of aldehyde and ketone changes on the flavor of wine
The chromatographic test results show that whether it is a reduced alcohol or a low-grade wine, after storage, the acetaldehyde content decreases, and with the prolongation of the storage time, the more acetaldehyde drops. Acetal is the opposite, i.e. the longer it is stored, the higher the content. This is because acetal is formed by condensation of acetaldehyde and ethanol:
CH3CHO+2C2H50H→CH3CH(OC2H5)2+H2O
Acetaldehyde ethanol acetal water
In degraded wines, especially low-grade wines, the ethanol concentration is low, and the speed of alcohol-aldehyde condensation is also slower.
The diacetyl content decreased with the prolongation of storage time, but it did not change much.
In summary, low-grade koji wine is an organic mixture of acid, alcohol, ester, aldehyde, ketone and other components, and its components themselves have a certain balance law and constitute a balance system. Through the study, it is found that the quality of reduced wine and low alcohol changes greatly in the storage process, the organic acid in the wine increases, the ester decreases, the aldehydes and ketones also have an upward trend, and the changes in the content and proportion of acids, esters, alcohols, aldehydes and ketones are the root causes of the taste and unpleasant taste after the storage of low-grade koji wine. Reducing wine and low alcohol, due to the significant change in the ratio of ethanol and water, resulting in a lot of alcohol-soluble trace components in the process of low-grade wine turbidity reduction, the slow hydrolysis of esters and the slow oxidation of aldehydes make the acid, alcohol in the wine increase, ester reduction. Therefore, in the production of denigration of koji wine, it should be noted that: (1) liquor should not be reduced indefinitely, especially the famous qu liquor should maintain its own unique style; (2) there are many factors affecting the quality change in the storage of low-grade koji wine, such as storage conditions (temperature, light, packaging container, sealing degree), sizing water quality (metal ions or non-metallic ions), turbidity removal methods (freezing, different adsorbents), etc., which should arouse the attention of manufacturers.