Why Does Wine Turn to Vinegar?

I saw an article in Food Network Magazine the other day offering the “perfect solution” for leftover wine after the holidays: making your own vinegar.

Now, I balked at the idea–first, because who has leftover wine at the end of the holidays (!?) and, second, isn’t that the very thing winemakers strive so desperately to avoid, seeing their hard work (artwork, even, if you will) literally reduced to vinegar?

Perhaps this struck a particular chord with me at the moment, as I am in the midst of studying for my Unit 2 Diploma Exam through the Wine and Spirit Education Trust (WSET), an international organization based in the UK that provides high quality education and training in wines and spirits. The Diploma is the WSET’s top qualification and takes approximately two years to complete; I’m approximately two months in and about to take my first of six exams, on viticulture (grape growing) and winemaking.

So, naturally, because I am currently ever-so-focused on understanding how to properly make wine, seeing the headline “Turn your wine into vinegar” made me want to shout “No, no, NO!” at the top of my lungs.

Fortunately for those sitting around me, I didn’t. However, the wheels started turning in my head and there’s no better way to learn than by teaching, right? And so, as much for your benefit as my own, here we have today’s lesson: why does wine turn into vinegar?

Mind you, I’m telling you this from a perspective of understanding and knowledge-seeking, not as a DIY tip for what to do with extra wine (which, really, you should never, ever have).

Let’s start with the basics. Wine comes from grapes (while you can ferment anything really, if it comes from anything else it must be labeled as such, i.e. “apple wine” or “pomegranate wine”). By the power of yeasts, the sugar in the grapes is converted into carbon dioxide, heat and, of course, alcohol.

Throughout the winemaking process, from the arrival of the grapes from the vineyard to the packaging in bottle, winemakers take care to avoid excess contact with oxygen, as this can have a detrimental effect on the final quality of the wine. The same gas that enables human beings to live and breathe on this earth has the opposite effect on wine: it destroys it.

You’ve probably heard before that red wine is “better” for you because it contains antioxidants. While that point is arguable, it is true that red wine does contain more natural antioxidants than white wines because many such compounds are contained in the skins of red grapes, and red wines are generally made with far more skin contact than white wines are to extract more color and flavors.

These antioxidant compounds, as their name suggests, serve to prevent the process of oxidation in the wine, which can cause a browning in color (in both whites and reds), a loss of flavors and aromas and, eventually, will turn that complex and delicious beverage into salad dressing, as you may have unintentionally experienced by leaving an opened bottle out too long.

Many people complain that red wine gives them headaches and blame the “sulfites” for their malaise. Yet, virtually all wines contain a level of sulphur dioxide, which winemakers rely on for both its antioxidant and preservative properties. In fact, because red wines have a greater natural protection, winemakers can–and do–add greater levels to white wines throughout the winemaking process. If you have ever opened a bottle and instantly smelled (or tasted) something resembling vinegar, that was a flaw. Either the winemaker didn’t take adequate care to keep oxygen out when the wine was made, or despite preventative efforts, some oxygen had seeped in (perhaps because of a faulty cork or poorly packaged bottle).

I know, I’m making oxygen sound like a bad thing, but just like anything else, it only becomes bad when it becomes too much. A little oxygen is actually needed to kick start the yeasts, or they won’t multiply and do their job (and you’ll wind up with a sweet, alcohol-free drink!). Likewise, a slow seeping in of oxygen as some of the best, most complex wines age in barrel and bottle is a good thing; both oak and corks are porous and allow some air contact (in fact, this is one of the arguments against screw caps for wines that need to age, as they keep oxygen out entirely, preventing the gas from making any changes to the wine).

It’s a complicated process determining the right amount of oxygen to let into a wine throughout its life, so perhaps you can see why deliberate oxidation of a perfectly good bottle would be so alarming to a winemaker!

That being said, if you really can’t finish the rest of that bottle, or you’ve simply forgotten and it has gone off, I suppose Food Network is on to something by not letting a good thing gone bad go to waste. I can’t imagine that Cabernet/Merlot vinegar would taste so bad.