(SFGate) - My column last Sunday, “Screw cap vs. cork? Many vintners say ‘Screw it,’” about how wines age under screw cap, generated a lot of passionate reactions in my email inbox. Who knew wine closures could get people so riled up? Wine-bottle hardware may not strike some of you as a controversial topic, but among wine geeks it’s a source of endless discussion.

The particular aspect of screw caps that I tackled in this column – whether these metal bottle closures can allow wines to develop and mature gracefully over time – is just one of many juicy screw cap topics that I’d happily geek out over. But print space (and reader attention span) is limited. So in case you’re curious about these things, here are a few more points I wish I’d been able to address.

1. “Cork taint” doesn’t have to come from corks. But it usually does.

When we say “cork taint,” we’re talking about 2,4,6-Trichloroanisole, or TCA, which is a chemical compound that can appear when chlorine interacts with certain fungi. This interaction tends to take place in wood-derived products. If that wood product touches wine, the wine will usually get infected with TCA, which is not dangerous to consume but which will overwhelm the wine entirely with its own distinctive flavor and aroma, masking the character of the wine. TCA is frequently described as having a “wet dog” or “wet cardboard” smell. Think chlorine, dank basement, moldy newspaper.

Although cork – which comes from the Quercus suber tree – is the most common entry point for TCA into wine, there are other woody materials in a winery that can potentially infect it, such as wooden pallets, cardboard boxes and even oak barrels. There have been instances in which wineries themselves have become “corked.” Under these circumstances, it’s possible that a wine bottled under a perfectly healthy cork, or under screw cap or synthetic cork, could suffer from TCA.

However, TCA from non-cork sources is pretty rare. Wineries no longer clean with chlorine products. If I were a winemaker, I’d be more worried about corks.

2. What’s the deal with screw caps and reduction?

No, I don’t mean a red wine reduction sauce. “Reduction” in this context refers to a winemaking practice that minimizes oxygen exposure. The opposite of “reductive” winemaking is “oxidative” winemaking. Most winemakers I’ve encountered aim to practice neither.

Reductive winemaking can preserve fresh, primary fruit, since it shields the wine from oxygen; however, an excess of reduction can also produce volatile sulfur compounds that have unpleasant smells and aromas. From here it gets pretty complicated. Suffice it to say that some of these compounds can make a wine smell like burnt rubber or rotten eggs. If you open a bottle of wine that smells like that, decant it or give it some air. In most cases, after a few minutes, the reduced characters should blow off.

So what do screw caps have to do with this? I spoke to a couple of people, including some sommeliers, who mentioned that screw caps “cause” reduction, because they don’t allow the same kind of oxygen ingress that cork does. This is not true. What is true is that screw caps won’t mask reduction if it’s already in the wine, whereas corks, which let more oxygen in, might. If you bottle a wine under screw cap that tastes reduced, it’s likely to taste reduced when you open it. But that’s not the screw cap’s fault.

If given the choice between a wine that tastes reduced or a wine that tastes oxidized (assuming that neither was the winemaker’s intent), I’d take the reduced wine any day. The reduced characters will almost always blow off, but oxidation is irreversible.

3. What are the environmental impacts of various wine bottle closures?

Cork is a renewable resource: It is harvested by removing the outer layer of bark from tree trunks, so the trees don’t have to be cut down. It takes a while for the tree to regenerate itself sufficiently to be harvested again – sometimes around a decade – but these trees can live for hundreds of years, so there’s no danger of a shortage. All good news.

Screw caps are made from aluminum, which is more polemical. Aluminum of course is recyclable, but it’s not clear how many wine drinkers actually recycle their screw caps. Aluminum is produced from an ore called bauxite, which is strip-mined. According to a study conducted by the Environmental Protection Agency, the production of one ton of aluminum generates about one ton of solid waste. Doesn’t sound good.

There’s a third road here: the synthetic cork. (Actually, there are even more roads, including glass stoppers and crown caps, but we’ll save those for another day.) Many synthetic corks are made from plastic, but Nomacorc, the most prominent producer, now offers a plant-based “cork” in addition to its plastic products. (What isn’t plant-based these days?) It’s made from Brazilian sugarcane. Nomacorc claims that this offers the best of both worlds: a sustainable resource that won’t contaminate your wine with TCA.

4. Screw caps need a re-brand.

In the rest of the New World wine regions, especially Australia and New Zealand, screw caps are used on wines at every point on the price spectrum. There’s nothing gauche in those countries about twisting open a $100 bottle of Barossa Shiraz or Central Otago Pinot Noir. My sense – and this is merely anecdotal, though bolstered by lots of other people’s anecdotal evidence – is that U.S. consumers are willing to accept screw caps for lower-priced wines, and for white wines that don’t require much aging, but reluctant to detach from the sentimental notion that truly great wine needs a cork. It’s ceremonious: Think about the ritual of wine in a restaurant, the server gently placing the extracted cork in front of your plate, pouring you a tiny taste (which, by the way, is so that you can check for TCA)