It was Louis Pasteur who first researched the process of maturation. He was asked to do so by the Emperor Napoleon III and his work drew quite a bit of attention for the first time to the importance of correct maturation. He showed by experiment that wine spoils when left in contact with air. During maturation wine is left to rest and the flavors in the wine to develop. Most wines, of all colors, are produced for early drinking and do not require much maturation time. Many finer wines, however, will benefit from some period of ageing, whether in bottle or cask. Maturation of the wine can take place in stainless steel vats, large oak casks or small oak casks. Small oak casks impart more oak flavors to the wine, among other things. To survive medium or long term ageing the wines will need high levels of tannin, acidity or alcohol, but more importantly must have high levels of fruit, my favorite characteristic in a wine. But, there are several other treatments that must be carried out before the wine is bottled to ensure that you are getting the best possible product.
Between the end of fermentation and the bottling (or packaging) process of the wine for sale, there are different steps that usually take place. A new wine fresh from fermentation is not a pleasant beverage; it is cloudy with yeast cells and has a dank nose of decomposition. Wine is a complex mixture of natural substances, many of which are in a constant state of change, not unlike myself. During the maturation process of the wine, polymerization occurs (technical stuff coming up), phenolic molecules combine to form larger tannin polymers, which eventually grow so large that they fall from the solution as sediment. The dead yeast cells and cellular matter from the grape (sediment) fall to the bottom of the fermentation vessel forming what is known as the “gross lees”. It is important to separate the lees from the clear wine, if left in contact with the wine this deposit will dissolve and impart an unpleasant bitter taste to the wine. Clarifying and stabilizing the wine is an important step and this involves racking, fining and filtering the wine.
Racking is usually achieved by pumping or siphoning the wine away from the lees into an empty container; this process also provides aeration and may help the formation of flavor compounds. The first racking takes place soon after fermentation and maturation and will be done at regular intervals until the wine is clear of sediment. As mentioned before, during the life of wine in bulk, a number of heavy particles will naturally fall to the bottom of the vat or cask, the wine will also contain a certain amount of lighter matter, which would naturally remain in suspension. To remove these particles, fining is the next process the wine will undergo to be sure that the juice is free of any haze-forming substances, which may cause problems after bottling, and to remove some of the tannins to improve the balance of the wine. In order to clear this matter there are certain agents which, when mixed with wine, will coagulate the suspension and cause it to fall to the bottom.
Fining is an ancient process of clarification; the original substances used were mostly of animal origin, such as milk, egg whites and even the blood of oxen, yikes! More modern fining agents are now used, depending on the color of the wine, there is bentonite, albumin (eggs), gelatine (not the kind you buy at the grocery store), isinglass (I’m not telling you what this is), casein (milk) and a few others. Bentonite is the most widely used fining at present. It is a type of powdery earth originally found at Benton in Wyoming. Curiously, its main use is in lubricating the drills used in the oil industry.
Fining removes colloids that cause cloudiness in the wine; filtration removes only particles. The process of filtration causes much controversy amongst winemakers. There are those who say filtration ruins the wine, and there are those who claim that when done properly there is no ill effect whatsoever. You certainly do not want the character of the wine to disappear with the unwanted particles. There are different techniques for filtering, but as a general rule of thumb, the finer the quality of the wine the more gentle the filtration will be, as long as stability can be assured.
After a healthy analysis, your wine is ready to be packaged. Wine can be packaged in glass bottles, plastic bottles (not ideal), aluminum cans, bag in box and cardboard tetra ‘bricks’ (milk and juice are commonly packaged in this). The tetra brick is an excellent form of packaging, low cost, with a good oxygen barrier and a good shelf life. If the winemaker chooses to bottle the wine, there are several options these days for which type of closure to use. The traditional closure for wine bottles has always been the natural cork. Several winemakers are moving away from the natural cork towards such closures as plastic, glass and screw cap. I could write an entire article just on “closures”.
But, I have done a lot of research on this subject and time and time again I keep hearing “The metal screw cap provides the best means of closure for glass bottles”. The screw cap provides the best oxygen barrier, they do not cause taint, they do not suffer from quality variation and they do not need a special tool for opening. The only down side of the screw cap is the negative image that it carries, some folks still associate the screw cap closure with “cheap wine”. The purpose of the closure is to keep air out of the bottle, it doesn’t matter what it looks like. It’s the juice in the bottle that matters.