A friend of mine was shocked when he saw me take a half-bottle of red wine out of the fridge and put it in the microwave. I zapped it for about 20 seconds, pulled the cork, and poured him a glass. He was, as the Brits put it, gobsmacked.

I was doing nothing wrong or abusive to the wine. Quite the opposite. In the previous week, I had a half-bottle’s worth of wine left over. So I had transferred it to a clean half-bottle, which I could fill to the brim, leaving no air space. I shoved a cork into the half-bottle and stowed it in the fridge.

This, in a nutshell, is how to deal with leftover wine, red or white. Despite all the gizmos on the market,I assure you that there is no better method of preserving a wine’s goodness. It has the virtue of being the cheapest approach as well as the best.

As for the various wine preservation gizmos, some of them work,to a degree.Others are hokum.One device, which is pure hokum, seems persuasive. It employs a small hand pump and a special flexible stopper.You pump the air out of a partially empty bottle, creating a vacuum.This makes sense, as air is the enemy of wine. Oxidation causes wine’s degradation.

Except there’s one problem: It doesn’t work. Laboratory tests show that immediately after pumping, the vacuum achieved is 70% to 75%. That’s actually pretty good.

But there’s a hitch: The stopper leaks. After two hours, you lose about one-quarter of the vacuum as air seeps in. After 12 hours, air has almost completely returned to the bottle.There’s just enough vacuum left to create a popping sound when you remove the stopper that leads users to conclude that all is well.

Then there are devices that replace air with another gas, such as nitrogen or argon.This is the premise of those wine-by-the-glass dispensing systems in restaurants, where slowly emptying bottles are preserved by a tank of nitrogen.

Do they work? Yes and no. Oxidation does appear to be reduced. But the hundreds of compounds that create the scent of a wine continue to be released in the bottle, never mind whether the gas in the bottle is non-oxidative. This taster’s subjective experience with wines preserved in this manner is that, after a day or two, the scent of the wine grows steadily more faint. And the taste lacks vibrancy.

Nearly everyone who works in a wine shop or restaurant with an expensive by-the-glass wine dispensing system can testify that the final glass served is noticeably different than the first glass from a freshly opened bottle.

So what does work? Cold.The aging of wine, at its most elemental level, is a matter of chemical reactions.After all, it’s just another solution to a chemist. The effect of heat upon wine follows a pattern commonly found in many other solutions, namely that heat accelerates chemical reactions. Cold slows chemical reactions.

A century ago, the Nobel Prize-winning Swedish chemist Svante August Arrhenius stated that if you have an increase of 18 degrees Fahrenheit, you should double the rate of the average chemical reaction. The same holds true in reverse: the colder, the less the rate of reaction.

Now apply this to a half-finished bottle of wine. By transferring the remaining wine to a clean half-bottle, you’ve eliminated the air space. That takes care of the oxygen problem, assuming a good seal. (A screwcap is even better than a cork, by the way.)

By putting it in the fridge, you slow chemical reactions, including oxidation from whatever air is still either in the bottle or in the wine itself.Your wine will last for days, even weeks, with surprisingly little degradation.

Much does depend on the type of wine. A mature pinot noir is very fragile.It won’t last long once opened no matter what. But most young wines, red or white, retain fresh, vibrant fruit. I recently reopened a 2004 dry riesling that had one glassful of wine removed from a full bottle that was left in the fridge for – get this – more than two months. It still tasted great.

I know of wine lovers who go to greater lengths yet. A reader, Fred Kawabata, wrote to me about how he transfers his leftover wine into sterilized beer bottles or smaller San Pellegrino water bottles.

Mr. Kawabata fills these bottles with leftover wine and then seals them with crown caps, the closure once common on soda pop bottles. (You can buy the caps and the simple lever device that affixes the cap to the bottle at any home brewing supply shop.)

Mr. Kawabata reports that he waits for at least a month before reopening the resealed wines, keeping them in his cool wine cellar. “I have been using this method for over three decades,” he says, “and have had only a few bad bottles.”

It all makes scientific sense: a cool environment, no airspace in the bottle, and a tight seal.And what about that business of quickly warming up a refrigerated red wine in the microwave, which so horrified my guest? Works like a charm, is all I can say. Twenty seconds of microwaving appears to do absolutely no harm.

By the way, a number of sommeliers in restaurants are known to discreetly perform this same trick on wines brought up from a cold cellar. They just don’t do it in front of their clients – and they don’t talk about it, either.