In nearly every question-and-answer session following a wine appreciation class, questions like, “What makes those old red wines so great?” and “How can a 50-year-old wine be so expensive?” inevitably emerge.

One part of the answer is tannin.

A nonwine example helps explain its characteristics most easily.

Imagine a very strong cup of tea. One sip fills your mouth with a dry, slightly astringent sensation. The liquid chemically robs your saliva of its slippery properties.

The astringency and “puckeriness” are memorable….and offensive. Tannin — aka tannic acid — is what you’re experiencing. Similar to the strong tea example, very young, highly tannic red wines are harsh and rather unpleasant. Overly tannic wines — and over brewed tea — are bitter.

However, given time, patience and appropriate cellaring conditions, big tannins contribute to making good wines great as well as long-lived.

Tannins are present in many, although not all, red wines. To make a traditional red wine like cabernet sauvignon, grapes are picked and gently crushed. The pulp, including seeds and skins, is put into large, open vats or in closed vats in a process called “carbonic maceration.”

The winemaker adds a strain of high-quality wine yeast. The entire concoction is thoroughly mixed and is then called “must.” During the process that follows, nature takes over — color is transferred from the skins to juice and the conversion of natural grape sugars into alcohol begins.

Depending on the variety of grape, and the stylistic decisions made by the winemaker, the time of skin contact can last from a few hours to a week or more. Tannin is extracted from the seeds and skins during this initial phase of fermentation.

If high-acid grapes are used, tannins are accentuated. Sweetness helps soften the impact of tannins in lighter wines. (Since white wines are usually picked, crushed and quickly separated from their skins, tannins are not a significant factor, especially if they are produced using stainless tanks vs. oak barrels.)

Along with alcohol and natural acidity, tannins act as a preservative and help give red wines their long life. It also affects smell and helps to provide a full “mouth feel.” Over time, either in a barrel or in the bottle or both, tannins soften, meld together with the many other components present and contribute mightily to what experts call “complexity.” Most of those 50-year-old wines would have been so tannic in their youth, they would have been virtually undrinkable.

Different grape varieties contain varying levels of tannin. Cabernet sauvignon seeds and skins contain many more tannins than those of a lighter variety like merlot.

If you drink either of those wines, imagine how each tastes different from one another. The ‘cab’ is heavier, has more mouth feel and is generally more complex. The merlot is lighter with more fruit upfront. If you look at the label, the cab is probably older than the merlot.

The expense part? Fruit of the quality that will stand up to extended aging is costly and often is from a great vintage year where grapes were sold at a premium. The barrels used are very expensive and are tied up, sometimes for decades.

The winemaker must constantly monitor the barrels for leaks and other potential issues. Once the wine is bottled, it likely will be sitting in a temperature-controlled cellar for additional aging and then too needs continual attention.

While all of the initial costs are up front, profits are decades away. Just like great Scotch, part of the price of that $50 bottle is based on fruit and equipment costs, time and the work of the winemaker.

For additional information on all things wine, email Donniella at dwinchell@ohiowines.org.