There are two good questions here...

First let me address the question of producing a wine like a commercial wine.  Some people claim they like homemade wine because it IS NOT commerical. Others like you and I would like ours to be more like commercials - characteristic of the grape or style and something you might think was purchased from a respectable wine shop.

To that point, when you say you want it to be more like commercial wines, you've got to zero in on the one you would want your wine to be like and analyze that wine for its qualities. What do you like about it? What don't you like about it?

Take that commercial wine and test it for final pH, acid, alcohol, and residual sugar. What type of grape? or is it a blend of several grapes?  Has it been on Oak? Is there a soft velvety mouth feel or buttery character that might indicate malolactic or partial malolactic fermentation?

You will basically use your goal to reverse engineer your wine.  So, now when you purchase your grapes/juice you know what you are shooting for. That coupled with good obsessive-compulsive recording keeping :-) and good winemaking practices will give you the best chance for creating something like what you had hoped for. If not, it should still be pleasant...

Tannin gives the impression of dryness in wine. It is that astringent feel we get in our mouths when drinking a wine heavy in tannin. In the right amount, the wine will present an interesting dimension and character. Without sufficient tannin, the wine will be flat and lacking character.

Tannins are naturally present in the skins, seeds, and stems of wine grapes. Because white wines or wines treated like a white wine during preparation are typically produced without skin contact, white wines are typically lighter in tannin than its red counterpart.

Amongst red wines, tannin will vary based upon the level of contact with skins. Some red wines, such as a Beaujolais, will have had minimal skin contact while others receive an extended period of fermentation on the skins. For a young wine, the extended contact can make the wine present a harsh dryness. Fortunately, tannin content is reduced naturally over time and harsh young wine can come into its own and in balance with the other characteristics of that wine. For the young wine high in tannin, the tannin acts as a preservative that will support extended aging.

Not all sources of tannin are equally ideal for influencing the character of wine. The two sources of choice for supplementing tannin in a wine are grape tannin and a strong tea solution. Grape tannin is said to be preferable because it is from the same source as wine and available in a known strength. The strong tea solution will also work, but the addition will be relative to the strength of the tea.

You might find it interesting to know that tannin content also influences how quickly wine will clarify. All things being equal, in comparison to a wine with a lesser tannin content, the wine with the greater content will tend to clarify more rapidly and without the need for additional finings.

Most meauring tannin is more of an art than a science and requires that you employ your senses to determine if tannin content is sufficient for the wine you are producing. As tannin content increases, it prgresses from a slight dryness and gets increasingly astringent. One key is developing a taste for tannin and understanding if your taste is more or less advanced then that of your intended wine drinking audience. For example, a common choice of new wine drinkers is Merlot over Cabernet. In addition to Merlot being more fruit forward than Cabernet, is has a noticeably lesser tannin content and is subsequently easier to tolerate for a newer wine drinker. Those with more developed taste may find that same Merlot a bit boring.

If your wine has low tannin; you can increase your tannin content by adding tannin to taste in the forms mentioned above.

If your wine is high in tannin; you can allow your wine to age and achieve a natural reduction in tannin. You can also opt to blend the wine with another wine that is lower in tannin. Still, another option is to directly remove the tannin through the use of a protein based fining agent. Historically Milk and Egg White have been used with success, but there is a question of the stability of these products which would require immediate racking. Perhaps a better solution for fining out tannin would be to use a gelatin solution. A good wine making book will provide further explanation on the use of gelatin, but 1/4 gram dissolved in water per gallon of must might be a good point to start at. After all, the goal is to reduce tannin content and not to strip it out of the wine.

In the end, a winemaker should have a disclaimer in his or her winemaking process that says "I reserve the right to adjust tannin in efforts to improve the character of my wine". Step 1 in doing so is to develop the tasting skill necessary to identify whether your wine is excessive or deficient in tannin. That will of course depend upon when you intend to consume the wine and your intended wine drinking audience.

Through aging, the rate at which the tannins reduce will depend upon the aging environment, but one sign of reduction is the precipitation of sediment as tannins change chemically (polymerize) during aging and fall out of solution. That is not to be confused with tartrate crystals which may develop during cold storage of bottled wine. The same polymerization also yields the color changes that are experienced as red wine ages.

I hope this helps...

- Nick Coppola
juicegrape.com support