Evolution of wine in the bottle

Esterifications of the wine in bottle

As wine is a hydroalcoholic acid solution, the formation of esters is normal. Acids (fundamentally) intervene in the esterification of wine. Ester is a combination of alcohol and acid.

Esterification reactions are very slow processes limited by reserved saponifications.

The phenomena of esterification has been held greatly responsible for the bouquet of wine. In our investigation of bottled Spanish wines, we have come to believe that, rather than being fundamental to quality, they can be considered in a positive sense as the fruit of a contained process of little importance in old wine. However they also have a notable incidence in negative processes. We have begun to attribute more responsibility to ethanol for the rancid taste acquired in ageing than to the inevitable common base of polyphenolic substances.

Esterification in the bottle is conditioned by acidity values and the nature of the acid, tartaric and acetic acid being predominant in the process. It is not so much the case with other acids. Actually, ethyl acetate is the dominant ester in numerous wines. It is held more responsible for the souring characteristic than acetic acid (vinegar) itself and its perception threshold is estimated at being between 180 and 200 mg/l.

In bottled red wines of the Rioja, the threshold in our tests of addition of ethyl acetate to the content determined by analysis is:

	Threshold value
Red wine of crushed grapes...............................	170 mg./l.
Red wine with CO2 maceration...........................	195 mg./l.

Ethyl acetate is basically a sign of degradation in quality and, as with volatile acidity, enologists are interested in achieving low values for consumption, around 100 mg./l. For this reason, it is convenient to know the circumstances which cause high or low levels of ethyl acetate.

On bottling, Rioja wines have levels between 60 and 100 mg/l. The highest levels occur in young wines under 12 months.

Later, in bottle, the level rises very slowly, depending on previous cleanliness during fermentation and in cask.

Sulphates in bottled wine

For organic purposes, we have studied the level of sulphates contained in bottled wine. They originate in the grape and increase with ageing.

A study of various wines which had been kept in bottle for different periods of time offered the following results:

Time in the bottle	Sulphates (g/l.)
15 - 20 years	1,7 - 2,1
10 - 15 years	0,7 - 1,1
5 - 10 years	0,6 - 1,0
2 - 5 years	0,5 - 0,9
0 - 2 years	0,4 - 0,9

It is easy to appreciate that evolution in bottle tends to increase the level of sulphates in the wine. But the samples studied show a considerable rate of increase after ten years.

Following the progress of just one product and controlling bottles at different times gave the following results:

Sample	Sulphates (g/l.)
Day of bottling	0,52
After one year	0,60
After two years	0,73
After three years	0,90

The increase is contained and is one more symptom of the complex ageing processes in bottles that undergo very slow oxidation.

Aromas of bottled wine

The aromas of Spanish bottled wines have not been studied individually or in groups. Our studies are based on industrial empiricism.

A unified quantity of red wine taken from a cask where it had been kept for two years was separated into smaller tempered units of stainless steel and bottled in monthly stages.

After a year, a control was carried out on the sample bottles of each bottled portion, controlling iron and initial red colour after 24 hours, and classifying the taste:

Wine	Wavelength 520	Wavelength 420	Iron	Class of aromas
Initial	1,6	1,62	2,2	Weak
After 1 month	1,48	1,54	1,7	Slight
After 2 months	1,47	1,58	1,3	Slight
After 3 months	1,43	1,63	0,9	Pleasant
After 4 months	1,38	1,66	0,6	Pleasant
After 6 months	1,41	1,64	0,4	Pleasant
After 12 months	1,40	1,63	0,6	Pleasant

In this wine, typical of the Rioja, there exists a rapid reductive process which manifests itself in the almost complete disappearance of ferric iron and the passing from a red colour to a variant. The colour decreases and returns with air contact. A parallel situation is observed in the aroma. Once the reduction point is reached, the aroma is pleasantly appreciated.

However, from the aromatic point of view, one appreciated feature is only developed in wines after one or two years in bottle. This is the reduction aroma of pleasing nuances for the Spanish subjectivity, it disappears from the glass after a few minutes.

In this type of wine there are three phases to the tasting:

• Inicial, de bouquet reductor de dos minutos en copa.
• There follows a neutral phase of some five minutes in the glass.
• Finally the wine gives off aromas of an oxidative nuance at the same time as that of the oak.

These three "readings" of the aromas of a wine with a long shelf life influence the winetasting experience. There frequently occurs in the A phase a "dry and harsh" aftertaste which is lost in phase B and is supplanted by another harsh nuance of oak in phase C.

Wine, in its aromatic aspect, goes through a crisis after some months in the bottle. It takes on a reduced character, expressing, very smoothly, the aromas assimilated in cask and later creating its own aromatic characteristics in the reduction process.

Compounds responsible for colour

In simple terms, we could define the subject of this chapter as the evolution of colouring matter in bottled wine. We must acknowledge that phenolic compounds and, more specifically, polyphenolic compounds, in addition to giving wine its characteristic colour, are, to a large extent, responsible for the aroma and taste.

Below, we offer a brief description of the evolution of wine from the grape to the moment it enters the bottle, assuming a normal maceration (in the case of red wine) and ageing in 225-litre casks for one to two years. A good comprehension of this process is essential to understanding the evolution of wine in bottle, also the relationship this has with previous processes and its consequences.

Wine arrives at the bottling plant after losing a considerable amount of anthocyanins during the time in cask (depending on the age of the casks). The tannin condensation process by polymerisation has already begun.

Although technical personnel work hard applying stabilising measures to the wine which is to be bottled, fortunately, when the product is received, it is in full polyphenolic development. At most, we stabilise marginal aspects such as microbiology or crystallizations, allowing its colour to evolve naturally.

In general terms, the evolution of wine in bottle represents a continuity of the activities which take place in cask, except for the absorption of tannin from the oak. Anthocynanins continue to disappear and tannins increase, in a clearly reducing environment. The cork represents a defence against oxidation. Any deterioration of the reducing power through the cork is unusual.

Depending on the variety, there are two types of colour evolution. Accordingly, we have established that wine ages in two different ways in bottle:

• Type I. Rapid change. Prototype: Garnacha (Grenache).
• Type II. Slow change and then stable. Prototype: Tempranillo.

This means that the colour of Garnacha ages very early and deteriorates very quickly.

In contrast Tempranillo ages very slowly, but later remains matured and stable for a long period of time.

This is due to the different evolution, or speed with which the red colour decreases and the yellow colour increases. Therefore, the colouring process which is present in cask, continues in bottle, but in the latter case, the process is much slower.

The reduction which is observed in the red colour is due to the destruction of anthocyanins. The yellow colour increases due to the joining of molecules, or polymerisation.

The development of anthocyanins (decreasing) and polymerisation (increasing) is sensitive to atmospheric temperatures. At less than 5° C, the process stops, it reaches its optimum level at around 30° C. However in practice, if there is a temperature variation during the conservation of bottles, not only does temperature have a bearing on its development, but it also provokes changes in volume (in temperature variations of more than 8° C). This means an interaction between the mass of wine and the mass of cork which could cause an imbalance in the normal reducing level. A bottle kept at 20° C deteriorates quicker than at 10° C.

The empty space between the cork and wine is necessary in order to absorb moderate thermal changes. An excessive space increases the oxidation of the wine in bottle, but an absence of this air space decreases the temperature changes causing regurgitations. This spoils the wine, entering the cork and then affecting the bottle.

Today, wine is usually bottled without air, in an inert atmosphere of nitrogen and carbon dioxide gas.

Alcohol in the bottle

When wines are aged for a long time in bottle, they seem to lose some alcohol through the cork, but do not deteriorate for this reason.

It is estimated that when stored in cellars with a 49-mm cork, a bottle placed in the horizontal position loses 1% of alcohol in 25 years, i.e., one degree; but this degree is lost as of the 15th year. For this reason, corks are changed in the case of wines which remain for more than 15 years in bottles.

Sediments in the bottle

Over the years, enological techniques have advanced greatly. In previous times wine was cloudy when bottled, maintaining a biological struggle between yeast and bacteria thus preventing the wine from becoming vinegary. Today, by extracting the microbian or crystalline agents of instability, it is possible to bottle wines free from the risk of turbidity and refermentations but with the natural activity of colouring matter. We can bottle stable wines without stopping the evolutionary process in bottle. Therefore, there is no technological justification for sediments of bacteria or wine-colouring matter.

The position of the bottle

In simple terms, it is recognised that the bottle must remain in a horizontal position so that the wine can dampen the cork and in this way, prevent it from becoming spoiled due to a lack of dampness.

Through several different studies of the relationship between wine and corks, we have determined that wine has a harmful effect on the cork. Different tests showed that polyphenolic matter present in wine attacks the cork and the degree of alcohol has a direct influence on the penetration of the cork mass by the wine. However, the most surprising results were obtained by the empirical testing of wines which were kept for ten years in bottle, some horizontal and others vertical. The corks extracted from horizontal bottles were of high density and low elasticity; while those of vertical bottles kept their initial density and were of greater elasticity. This means that wine can deteriorate the cork once in bottle. We are not so bold as to make recommendations against storing in the horizontal position, but this is under review.

The open bottle

On some occasions, doubts arise concerning the advisability of opening a bottle and drinking the wine immediately, or, of allowing some time to elapse between these two events.

The data we have accumulated generally advises that wine be consumed very quickly, soon after the cork is removed from the bottle. However, we cannot advise against consuming wine after a degree of contact with air. After the bottle has been opened, wine undergoes three changes:

• An immediate change in which reduction can be observed.
• Later, there is a time of neutral aromas. After some hours there is another evolution of the flavour.
• The appearance of lively aromas with a certain degree of oxidation.

The amount of time which elapses from phase I to phase III depends on the iron content. 24 hours for wines open to the air with total iron of more than 8 mg/l, and slower if the iron content is lower.

In general terms, Rioja wine does not require breathing before consumption.