How to bottle wine at home: 6 tips to avoid oxidation

Bottling is one of the most exciting steps in winemaking. At last, you get to taste and share the fruit of all that effort! On its way out of the vat and into a bottle, though, the wine will be briefly exposed to oxidation and unwanted bacteria. So you need to be extra careful to avoid “breaking” the wine by bottling it, to avoid favouring the appearance of “corked wine,” or to avoid introducing contaminants that, in the long run, will affect its taste qualities.

So in this article I’ve gathered 6 tips that I apply when it’s time to bottle my wines.

Check that malolactic fermentation is finished

It’s the first thing to check, because if malolactic fermentation (MLF) isn’t finished, it risks carrying on in the bottle. That resumed activity will produce carbon dioxide, making the wine slightly sparkling, which may be unwanted depending on the style of wine you’re after and could even be enough to push the cork out!

4 ways to check that MLF is finished

1. Monitor the cuvée continuously: A few weeks or even a few months after alcoholic fermentation (AF) ends, the wine will start fermenting naturally again. By monitoring your wine continuously, you can therefore notice it, because the airlock will become active. Once MLF is finished, the airlock will go quiet again and the surface of the wine in the vat will be perfectly smooth. Finally, very experienced people will also be able to taste the change caused by MLF.
2. Bottle a single bottle: I agree it’s not always easy to monitor or taste your vat every week. Moreover, if it’s kept in a cool place (e.g. a basement or on a concrete garage floor), malolactic fermentation (MLF) risks being slow to start. A simple method is to bottle one bottle and leave it on the kitchen counter, at a temperature of 21 to 23°C. After three weeks, if no gas is released on opening, that indicates MLF was already finished.
3. Use chromatography paper: This specialized paper lets you see with the naked eye the presence of the wine’s 3 acids (tartaric, malic and lactic). I won’t go into the details of the procedure here because it’s complex, but basically, since MLF converts malic acid into lactic acid, the trace lactic acid leaves on the paper will grow and the one malic acid leaves will shrink.
4. Send your wine to a lab: It’s the most effective method but also the most expensive. A private lab can precisely measure the different amounts of acid: when the amount of residual malic acid is below 0.2 g/L, MLF is considered finished according to OENOQUEBEC (PDF in French).

Do a light sulphiting the day before bottling

Transferring the wine will necessarily incorporate a little oxygen into it and, by the same token, oxidize it. Yet it turns out that sulphites, in addition to their antiseptic properties, have antioxidant properties. A light sulphiting at 20 ppm (or 20 mg/L) of free sulphites the day before bottling will therefore give the sulphites time to distribute evenly in the wine while activating their ability to protect against oxidation.

For a step-by-step guide to sulphiting, see the section “Know how to add sulphites to your wine” of my article Potassium metabisulphite in wine: how much, when and how.

Clean and sterilize the bottles thoroughly

Wine, after fermentation and stabilization, is always vulnerable to outside contaminants. So you absolutely must:

• Clean all the bottles and the bottling equipment (capper, corker, siphon, etc.) with an unscented or lightly scented dish soap; and
• Sterilize all the bottles, the equipment and the corks (or caps) with sulphited water (1 teaspoon per litre of water) or an oxygen-based sanitizer such as One Step.

Note that a small amount of sulphited water or sanitizer (more or less 60 mL by eye, ~1/4 cup) will be enough to sterilize a bottle. Just put your thumb over the neck, then shake vigorously.

How to prevent corked wine?

“Corked wine” is caused by TCA (trichloroanisole), a molecule that forms when fungi naturally present in cork come into contact with chlorine. The result is that the wine has that characteristic little taste of wet cardboard or damp basement.

That’s precisely why the sulphited water and oxygen-based sanitizers like One Step mentioned above are recommended over a chlorinated product. Using bleach is a reflex that seems harmless but is one of the most avoidable causes of this flaw.

That said, a good part of the TCA risk comes from the cork itself, even before it enters your cellar: favour a reputable supplier and store your corks in a dry place, away from humidity but above all from pool chlorine.

Transfer the wine into the bottles without oxidizing it

On top of tip #2 (light sulphiting the day before), there are 3 precautions to take here during the bottle-filling step to prevent premature oxidation of your wine:

1. Do the work when the temperature is between 12 and 16°C: That range is the temperature of a classic wine cellar and is optimal because it keeps a maximum of carbon dioxide (CO₂) in the wine. This naturally present gas will try to escape during bottling, creating bubbles and therefore oxidation. Realistically (who has a wine cellar at home?), it will be enough to bottle in the evening or very early in the morning, and ideally in your basement, your garage or an air-conditioned room.
2. Reduce the splashing caused by siphoning: By holding your siphon against the wall of the bottle, the liquid will transfer without splashing, whereas if the siphon is in the middle of the bottle, the flow will be thrown into the empty space and splash all over inside the bottle. Keep in mind that the more it splashes, the more air gets into the wine and oxidizes it.
3. Minimize contact of the vat and the bottles with the air: Once your vat is open, the gas it holds will escape (there’s always a little that has been released naturally) and the vat will be exposed to air. So you have to rack it quickly, that is, with as few interruptions as possible and minimizing the amount of air that can get in. Same with the bottles: as soon as they’re filled to the right level (see the next tip), you have to cork them without waiting.

Fill the bottles with the right amount of wine

There you go, the bottles are filled and, as discussed earlier, they should be closed as quickly as possible with a corker. Be careful, though, to check the wine level in each bottle before putting the cork in!

It’s critical because for the wine to keep optimally and without fuss, you need to leave a gap of 1 to 2 cm between the cork and the wine:

• Less than 1 cm and the cork could be pushed out by the wine when it expands in high temperatures (30 to 35°C);
• More than 2 cm and the air trapped in the bottle could oxidize the wine, ruining all the efforts made so far to protect it.

What about a natural sparkling wine (pét-nat)?

Since a pétillant naturel will be put under pressure by the fermentation that finishes in the bottle, the space between the crown cap and the wine has to be larger (between 3 and 4 cm) to prevent an overpressure that could unseal the crown, or worse, make the bottle burst. To gauge the level properly, the same pro tip applies: the new cork!

Choose the right bottle-aging time

In theory, nothing stops you from opening your bottle the week after bottling. In practice, you’re better off waiting at least a month: that delay lets the flavours, temporarily thrown off by the handling of the wine (a phenomenon called “bottle shock”), settle back into place.

What’s the difference between a clear bottle and a green (or brown) one?

Once past the one-month mark, the optimal keeping time will depend mostly on a sometimes forgotten factor, the colour of the glass:

• A clear bottle offers almost no protection against light. Prolonged, close exposure will thus alter the wine’s aromas over time. It’s then better not to go beyond a year of aging and, ideally, to store it away from all light during that period.
• A green/brown bottle filters a good part of the UV rays. That allows for longer keeping, but be careful not to simply forget it at the back of the cellar: you need to taste its evolution regularly, and as soon as the wine starts to decline rather than improve, it’s a sign it’s time to drink it.

That’s the recipe for a successful bottling. All that’s left is to design the labels!