I intended to write today’s column on the use of oak in winemaking. It’s such a broad, complicated topic that I figured some attempt to present the basics might be helpful. It didn’t take me long, though, to realize that even the most rudimentary discussion of oak relies on so many other basic facts about winemaking that beg explication first.

To understand what oak does to wine, one needs to touch on primary fermentation, malolactic fermentation, lees, battonage, micro-oxygenation, aging and more. We need to know how grapes become wine before we discuss a particular approach to the process. Far fewer wine drinkers understand how oak affects wine than profess to either “like” or “dislike” wines that see oak.

It’s like a conversation where at some point you’re distressed to realize that you’d incorrectly assumed everyone involved agreed at least on the terms under discussion. We dive right in, our habits and partial ignorance intact and unexamined, happy if we merely got to “express our opinion.” Usually, a touch of sadness lingers: Something at the core of the matter remained hidden; we talked past each other.

What follows is a humble attempt to avoid the sorrow of half-conscious dispute. It’s a run-through of the basic steps involved in making a still (not sparkling) wine. I hope it can serve as a sort of sourcebook for subsequent discussions of the details and finer points. The dream of a common language too often remains a dream. But we do what we can to bring it to life.

A MAGICAL MARRIAGE

The first thing to know is that grapes are a magical potential marriage of yeast and sugar. “Potential,” because the yeast is on the outside, on the skins, and the sugar is on the inside, in the pulp. The wedding occurs only if the outside and inside meet; this happens when grapes are crushed. Yeast loves sugar, consuming it ravenously to produce alcohol, heat and carbon dioxide, a process known as fermentation.

In that simple statement lie worlds of choices the vintner must confront. Fermentation takes a little time to get started on its own. First comes maceration, the pre-fermentation period during which the goopy mass of crushed grapes, seeds, juice, stems (if the grapes weren’t previously destemmed), and skins get to know each other. Because the flesh of almost all grapes is colorless, it is skin contact during maceration that tints a final wine red. A wine ends up white only because the ripened skins (often quite a dark grayish or pink color, even in white-wine grapes) are separated from the juice before they can dye the wine.

It is also maceration that explains rosé. I often get the sense that people conceive of rosé as a strange “other” category in wine, a form invented recently to coincide with summer vacation. In truth, rosé is just another point along the spectrum of vinification: Red-wine grapes are crushed but left to macerate on skins for only a few hours.

NATURAL VS. ARTIFICIAL

As heat rises after maceration, fermentation feels welcomed to commence. (With the advent of refrigerated tanks, vintners gained the ability to sustain maceration for longer periods of time by lowering temperature – an approach known as cold-soak, which can be used to compel more extraction of flavors and concentration in the finished wine.)

Fermentation takes place in vats, either sealed or unsealed, made of wood, stainless steel (usually temperature-controlled), clay or concrete. If in wood, oxygen becomes part of the process. If the vat is unsealed, the ambient yeasts of the winery itself participate in the fermentation. Most modern wines are not fermented with the ambient yeasts and do not even rely on the native yeasts from the grapes’ skins, since native-yeast fermentations are more difficult to control. Instead, they are fermented with cultured (or inoculated) yeasts, produced commercially in order to produce more reliable wines, more quickly, with more consistent profiles.

Many contemporary wine enthusiasts feel that the use of cultured yeast is a sort of cheat. Morally, it is seen as a foreign element and therefore its product is not a true wine. Enologically, because it is, objectively speaking, an artificial crutch, cultured-yeast fermentation yields wines less capable of surviving on their own. For a finished wine, survival means protection from oxygen. Therefore, cultured-yeast wines usually require (or at least receive) the addition of more sulfur dioxide (a protectant from oxidation) than native-yeast wines.

Proponents of natural wines do not all agree on the characteristics of the category, but one firm principle is that organically grown grapes are fermented only with native yeasts.

Back to fermentation. During the yeast’s consumption of sugar, carbon dioxide is released. This is usually allowed to escape, but sometimes, especially in whites, some CO2 is retained to add to the sense of refreshment in the wine. If you’ve ever had a traditional wine from Vinho Verde (a region in Portugal, not a specific type of wine) with lots of effervescence, that’s how it got there. (To confuse matters, though, some Vinho Verde producers actually add CO2 as well.)

A wine can be fermented fully, where the yeast consumes all the sugar in the juice, yielding a dry wine. Or fermentation can be halted at some point, by lowering the temperature of the vat, which leaves some residual sugar in the wine. German Riesling is most famous for this, and historically occurred naturally as the late-autumn temperatures in that high-latitude region dropped enough to stop fermentation prematurely. German Riesling’s extraordinarily high acidity, though, is complemented by the residual sugar in off-dry expressions, yielding a final wine that tastes balanced. There are many other wines with residual sugar, however, most infamously California chardonnays made as Kendall-Jackson’s is. The popularity of that wine led to the wine-industry truism that people “talk dry but drink sweet.”

GROWING UP

After fermentation, the wine is drained or pumped off the skins into a vessel for aging. Even that choice – whether to drain via gravity or pump via mechanics – is a topic for vintners to dispute, by the way. The vessel for aging can be wood, clay, steel or concrete, of various sizes and shapes, each with its particular benefits.

A wine that ages in wooden barrels will usually undergo malolactic (or secondary) fermentation. Almost all reds and some (sturdier) whites undergo “malo,” as it is called, the result of interaction with agreeable bacteria in the barrel. Malo is the conversion of the wine’s rather harsh green-apple-y malic acid into a softer, milky lactic acid. Malo can sometimes occur during primary fermentation, or at the beginning, middle or end of the aging process. According to temperature, it will occur naturally, or not; it can be prevented (by lowering temperature), or not. White wines that have undergone malo are richer and butterier; those that have not are racier and leaner.

Aging can occur for months or years and aging wines can be left alone or manipulated. The main way of manipulating an aging wine is racking: moving the wine from one vessel to another in order to settle out the solids and remove the clarifying liquid, and to introduce oxygen which can in controlled ways help the wine mature.

If left unracked, a wine will eventually come into contact with its lees – the dead yeast cells resulting from a finished fermentation. Lees contact, over weeks or months, can produce a more complex wine with more textural richness; racked off the lees, a wine will express relatively more clarity and crystalline texture.

FINING AND FILTERING

Finally (well, nothing’s really final, but …), before bottling a wine may be either fined, filtered, both or neither. Fining involves the addition of a coagulant, which attracts the tiny solids that remain after fermentation, racking and aging. These solids, which contain some tannins, then settle to the bottom of the tank rather than making it into the final wine, or they can be removed more thoroughly through filtration. A fined and/or filtered wine will be, all other aspects equal, smoother and clearer but with somewhat diminished character, than one that is unfined/unfiltered. As you can imagine, all sorts of disputes – gustatory, ethical, philosophical, emotional – surround these.

You probably won’t be surprised to hear that the above narrative barely scratches the surface of what it takes to make a wine. But it’s the basic way that glass with dinner came to be. Wines are born, yes, but wines are also made. Keeping that oft-ignored fact in mind as we taste will serve us well for future conversations.

Joe Appel works at Rosemont Market. He can be contacted at:

soulofwine.appel@gmail.com