What happens during process of aging wine?

After alcoholic fermentation, aging is the next most major important stage of the wine production process. Aging changes the character of a wine in many of the same ways that it changes the character of human beings: they become deeper, more mellow and more complex.

Based on the style of wine, aging time may vary, and it may be a few months to several years.

Traditionally, aging is carried out in oak barrels that are stored in damp cellars where humidity protects the barrels from drying. Aging in barrels may also be for only a limited time and then the wine may be transferred to larger casks or tanks for further aging.

Biological aging 
There are two main types process for aging: biological aging and oxidative aging. The biological aging process involves various changes in wine composition.

Such changes are essentially the result of the metabolism of flor yeast and to a lesser extent, of other phenomena common to all types of aging processes including crystal precipitation, chemical reactions between wine components and extraction of substance from cask wood.

During this time, the wine undergoes malolactic fermentation and often develops a thin layer of yeasts on its surface.

Flor yeasts can undergo autolysis during biological aging of wine. This biochemical process occurs under special conditions such as those in wines stored and aged in contact with yeasts for months or even years. The yeast coming from either from grapes or previously used barrel.

Oxidative aging 
The oxidative aging occurs without flor yeast activity. During the aging process, some of the substances responsible for the fruity character in the one are oxidized by oxygen.

Barrel wood plays a role as a type of tissue of semi-permeable membrane to oxygen, allowing it to be incorporated into the wine at just the right rate.

A small amount of oxygen in an aging wine helps tannin, molecules polymerize and settle, softening a wine’s body and making it less bitter.

The aging process improves the overall quality of wine, including aroma, color, clarity, taste and mouthfeel. 

Different flavor and aroma enhancing compounds are formed during aging, and in the traditional aging process, the wooden barrel used for storing the wine also contributes to improving the flavor; especially, gives an oaky flavor to aged wine. The aging of wine success depends on a number of physical, chemical and biological factors.
What happens during process of aging wine?