Wine Culture and Information - Volume 13
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  Corkscrew Issue 53, June 2007   
Making Wine: AgingMaking Wine: Aging  Contents 
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Making Wine: Aging

Aging is a fundamental process allowing the production of a wine with more rich and complex organoleptic qualities, a process depending on type of grapes and wine

 Wine, according to a technical point of view, is ready at the end of alcoholic fermentation. A wine which is still immature, rich of young and unripe qualities, however considered a wine according to every point of view. Sugar, because of the effects of yeast, is now transformed into alcohol, aromas - because of fermentation - are now developed, so far from the ones of grape and of must. Whether according to a technical point of view the wine is now ready, the same cannot be said according to an organoleptic point of view. Soon after fermentation, wine is in fact hazy, with many solid parts in suspension, acidity is pretty evident - a quality which is however welcome in most of white wines - and in red wines astringency of tannins is pretty aggressive. The “cure” to all of these young qualities is represented by time which, together with proper wine making techniques, will give a more mature wine, with agreeable and pleasing organoleptic qualities.


Cellar: the place where the wine ages
inside casks
Cellar: the place where the wine ages inside casks

 The phase between alcoholic fermentation and bottling is called aging, period during which wine develops and changes, also thanks to the fundamental role of oxygen, it becomes more stable while losing the typical young character. Indeed, the aging of wine continues - although by means of different ways and natural phenomena - inside the bottle. Bottle aging is in fact very important and allow the wine to get improved by “refining” all the qualities found in a ready wine. Despite aging is a fundamental phase for every type of wine, indeed its practice and duration varies according to many factors, such as the type of grape, vinification technique and type of wine. Aging is then part of the “natural” biological cycle of wine, however different for each of them, by following an evolution beginning with youth, therefore developing towards the apex of aging - that is when the wine will have its best organoleptic characteristics - and then moving to its decline, a period during which the wine goes towards its inexorable end.

 

Containers for Aging

 The choice of the container to be used for the aging is done according to the type of wine to be made, the quality of grapes and the wine making techniques. Every wine is different from any other, therefore the practice of aging will change according to the wanted result. In most of the cases, whenever it is thought about the aging of wine, the type of container commonly associated to this process is the cask, however this is not the best choice in every case. Every container has in fact proper qualities and characteristics making it suitable for the aging of specific wines and therefore unsuited for the aging of others. It was already mentioned oxygen plays a fundamental role in the aging of wine, however this is not the only factor contributing to the development of the entire aging process. Other factors influencing aging of wine include the type of container, temperature, humidity, light and keeping practices, such as topping ups and rackings, as well as - of course - specific qualities of wine.


 

 Every type of container offers advantages and disadvantages for the aging of specific wines, moreover it must be considered containers belonging to the same type are different one from another, with proper characteristics and qualities. For example, if we consider the cask, belonging to the category of wood containers, the definition is pretty generic as every cask is different from another because of volume, type of wood and thickness of staves. All of these characteristics directly influence the aging of wine, therefore it will be chosen according to the wanted result. For example, the type of wood, volume and thickness of staves directly influences the quantity of oxygen reaching the inside of the cask from the outside, as well as the passage of internal substances to the outside. Moreover, the type of wood - its area of origin and the type of tree from which it is obtained from - besides having an absolutely proper porosity, gives the wine specific organoleptic qualities, different qualities and quantities of tannins, also determined by the level of toasting with which the wood was processed during the construction of the cask.

 Of all the types of containers used for the aging of wine, only the ones made of wood play an active role, they give the wine their own organoleptic qualities and allow the participation of oxygen. All the other containers - as they do not have these two qualities - are generically defined as inert, that is made of materials having no capacity of changing the organoleptic qualities of wine, such as stainless steel and glass. The main inert containers are represented by steel tanks, cement and fiberglass vats, demijohns and bottles. If it is true inert containers do not allow the passage of oxygen - of course provided proper keeping conditions are adopted - it should be considered they are however sensitive to temperature, a factor influencing the speed of aging. In case are used glass containers - such as demijohns - another factor should be considered as well, in fact by passing through the glass, it influences the aging and stability of color, in particular in white wines.

 The case of wood containers is more complex, not only for the fact they allow the passage of oxygen through the pores, but also because they are made of organic material and therefore playing an “active” role. In wood containers - casks, barrels and barriques - also happens the passage of wine, water and alcohol in particular, from the inside to the outside, a phenomenon causing both the concentration and the diminishing of wine and therefore requiring frequent topping ups. As the aging in cask is strictly associated to the quantity of oxygen reaching the inside through the pores, this factor is widely determined by volume, type of wood used for the construction - therefore the grain of wood and stave thickness - as well as temperature. The smaller the volume of the cask, the quicker the aging and the effect of oxidation: wine ages quicker in barrique than in a cask. Casks are made of different types of wood, each of them having absolute proper characteristics, of which the most common types are oak, chestnut and cherry wood.

 

The Aging of Wine

 The aging of wine is the result of a series of phenomena occurring during a period of time and in which oxygen plays a role of primary importance. In wood containers, oxygen reaches the wine thanks to the porosity of wood, ensuring a flow in extremely reduced quantity although continuous. Oxygen also plays a fundamental role in the aging done in inert containers and, despite the keeping is done in order to avoid any contact with the air, the oxygen however gets in contact with the wine during the operations of racking. The role of oxygen in the evolution of organoleptic qualities of wine also continues at the end of aging, when the wine is finally bottled. In bottles closed with corks it in fact occurs an exchange of oxygen from the outside to the inside of the bottle through the pores of the cork itself. This process is fundamental for red and white wines destined to the aging in bottle, whereas for white wines not suited for aging, the contact with oxygen causes the loss of fresh and fruity organoleptic qualities.

 The phenomena taking place during the aging of wine are divided into three categories: chemical phenomena, physical phenomena and physical-chemical processes. Chemical phenomena are represented by oxidation and oxyreduction, esterification, condensation and copolymerization; physical phenomena include saturation, precipitation of solid substances, evaporation, loss of carbon dioxide. Physical-chemical processes are mainly about flocculation and sedimentation, indispensable to get a limpid and stable wine. These processes occurs for all the duration of aging - therefore for all the life cycle of wine - including the period of aging in bottle. The velocity and the time required for the development of these phenomena depend on many factors of physical and chemical nature occurring during aging, last but not the least, on the specific qualities of grapes and the type of vinification. For example, in wines produced with Nebbiolo or Sagrantino grapes, aging processes are slower than in the ones occurring in wines produced with Freisa or Grignolino.

 As the oxygen is the most important factor in the aging of wine, oxidation is therefore the main chemical phenomenon. The bond between wine and oxygen is very strong, not only it is indispensable for the aging, but it also gets rapidly combined to many elements contained in the wine, therefore causing oxidation. Oxygen dissolves in the wine both during the aging in wood containers as well as during the operation of rackings and bottling. Oxidation of wine is a process essentially concerning some components only, such as tartaric acid, alcohol, polyphenolic substances and coloring substances. Tartaric acid - in pure solution - it is not subject of any oxidation, however in presence of iron or copper occurs its oxidation and degradation. Oxidation of tartaric acid is very important for the development of the so called tertiary aromas, that is the aromas developing with aging. Also alcohol, because of the bond with oxygen, get oxidized and produces acetaldehyde, also known as ethanal.

 More important is the oxidation of polyphenolic and coloring substances. Oxidation of polyphenolic substances - commonly defined as tannins - is something usually happening in red wines only. Oxidation of polyphenolic substances produces a strong diminishing of wine's harshness and its astringency. Oxidation of polyphenolic substances is very important for the improvement of organoleptic agreeability of a red wine, in particular wines produced with grapes rich in tannins, such as Nebbiolo, Cabernet Sauvignon and Sagrantino. Besides oxidation, with time polyphenolic substances change as well, they aggregate and form bigger molecules, giving origin to polymers. This transformation makes the astringency less aggressive, in other words, the wine gets smoother and more pleasing. With time, these aggregates of polyphenols move to the bottom therefore forming a sediment, a phenomenon which can be sometimes observed in bottle of red wines aged for a long time and produced with grapes rich in polyphenolic and coloring substances.

 The oxidation of coloring substances is a phenomenon occurring both in white and red wines. In white wines the color gets darker hues of golden yellow, whereas in red wines purple hues are soon replaced by ruby red, then garnet and finally brick red. In white wines the color can also change in consequence of the oxidation of alcohol, with an abundant production of acetaldehyde, causing a strong change in color with golden or amber yellow hues, sometimes developing some faults such as excessive acidity. The result of these phenomena is commonly known as maderization. The development of oxidation is determined by the presence of some factors. High temperatures accelerate oxidation whereas lower temperatures favor the dissolution of oxygen. Some substances found in wine, such as polyphenols, sulfur dioxide and some acid substances, make the oxidation of some wine's components difficult: this explains the slow aging of wines produced with grapes rich in polyphenolic substances.

 The esterification is another important phenomenon taking place during the aging of wine. Responsible of esterification is the reaction between alcohol and the acids found in wine and which give origin to esters, such as ethyl acetate and ethyl lactate. Only volatile esters influence the aromatic profile of wine, most of the times responsible for unpleasing aromas. During aging it is also observed the precipitation of potassium bitartrate in the form of crystals settling on the bottom. This precipitation produces a diminishing of acidity only and it is mainly observed at the end of wintertime and cold season. Just like in every sedimentation phenomenon taking place in a wine, a racking allows the elimination of potassium bitartrate crystals. Lastly, when the aging is done in wood containers, after some years it is observed a loss of alcohol caused by evaporation. The quantity of lost alcohol essentially depends on the volume of the cask and the grain of wood, however it is generally from 0.2 to 0.3% a year.

 




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  Corkscrew Issue 53, June 2007   
Making Wine: AgingMaking Wine: Aging  Contents 
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