Hardly a word in the wine cellar causes as much unease as “sulphur”. Headache fear, “chemicals in the wine”, the whole programme. I hesitated myself in the past. In 1998 I wanted to age a Riesling as naturally as possible and skipped the sulphur addition after fermentation. Six weeks later the whole demijohn smelled of nail polish remover and vinegar. Twenty litres, gone. This lesson taught me what sulphur actually is: no poison, but the oldest and most reliable tool for keeping wine alive.
Why sulphur has belonged to wine since Roman times
The Romans burned sulphur in their amphorae and wooden barrels before they filled the wine in. The acrid smoke, sulphur dioxide, cleaned the vessel and laid itself protectively over the wine. What antiquity did from experience, we understand chemically today, the principle has stayed the same for over two thousand years. Sulphur dioxide, SO2 for short, is the actual effective substance. In the hobby cellar it usually comes into use not as a gas but as a powder: potassium metabisulphite, E224 on the ingredient list, which releases about half its weight as active SO2.
What SO2 really does in wine
SO2 does two jobs at once, and both are worth understanding.
Oxidation protection
Oxygen is the silent enemy. It browns white wine, eats fruit and bouquet and turns living wine into tired, maderised wine. SO2 catches the intermediate products of oxidation, above all acetaldehyde, that substance that makes oxidised wine smell old and sherry-like. Free SO2 also stays in the wine as a reserve and works on when air does get at it after all: during racking, transferring, bottling.
Microbiology
The second job is police work. After fermentation your wine is a buffet for everything that ferments and sours: wild yeasts, lactic acid bacteria and above all acetic acid bacteria. The latter need oxygen and turn alcohol into acetic acid. That was exactly my downfall in 1998. Free SO2 keeps these microbes in check. How well depends on the pH value: the more acidic the wine, that is the lower the pH, the more of your SO2 is in the effective molecular form and the less you need.
When you sulphur
Two fixed dates, and in between as needed. The first addition comes when the fermentation is really through, usually at the first racking off the yeast. Before that you don't sulphur, otherwise you slow down the cultured yeast that is just doing its work. The second addition comes shortly before bottling, because here the wine gets plenty of air once more and is meant to keep for months in the bottle afterwards. In between, the professional measures the free SO2 and tops it up. As a hobby winemaker you do well to dose cleanly and conservatively at these two dates.
How much? Conservatively and by the pack
Here craft parts ways from fear and from recklessness. Too little, and the wine tips. Too much, and you smell the sulphur in the glass, a pungent match note. As a rough orientation, many aim after fermentation for 30 to 40 mg/l of free SO2, with white wine and sweet wine a little higher than with dry red wine. How many grams of potassium metabisulphite that means for your number of litres you don't work out from the gut: it's on the pack, and there you stay at the lower end. Dosing conservatively is no new fashion, the old cellar books preach it, from the Kitzinger Wine Book onward, for over a hundred years.
The legislator draws the upper limit for dry red wine at 150 mg/l total SO2, for dry white and rosé wine at 200 mg/l. With clean work you're far from these values. And from 10 mg/l onward, “contains sulphites” must go on the label, even for your house wine if you give it away.
In practice: I always dissolve the powder first in a mouthful of wine or in boiled, cooled water and then stir this solution evenly into the whole batch. Never tip the dry powder straight into the wine, it clumps and over-sulphurs one spot and the rest not at all.
Alternatives and honest limits
Can you do it entirely without sulphur? Yes, but be honest with yourself. Unsulphured wine is short-lived, prone to oxidation and an open door for acetic spoilage. It demands impeccable hygiene, cool storage, brim-full vessels without an air cushion, and that you drink it promptly. There are aids that support the sulphur but don't replace it:
- Ascorbic acid (vitamin C): reacts quickly with oxygen and complements SO2 well, but works only together with it, never alone.
- Inert gas like CO2 or nitrogen displaces the air over the wine in an opened container.
- Sterile filtration removes yeasts and bacteria mechanically, but needs the appropriate equipment.
All of that is fine work and doesn't replace the basic safeguard of a little free SO2.
Sulphur wicks for the barrel
The second face of sulphur is cellar hygiene, and there we're back with the Romans. An empty wooden barrel is, without treatment, a biotope for mould and acetic bacteria. A sulphur wick, hung on a wire and burned in the empty barrel, fills the interior with SO2 gas, kills what lives there, and takes must and off-odours with it. Important: air out well and don't inhale the gas. And take a wick that doesn't drip, so that no burning sulphur falls onto the staves and leaves an off-note there. Amount and burning time depend on the barrel size and are on the pack. For storing empty barrels through the summer, this is the classic method to keep the wood clean and odour-free.
Two things that stand on my shelf. For the wine itself I take the Joenos Wineguard sulphite powder, because it combines the potassium metabisulphite with a little ascorbic acid: the SO2 does the long-term work, the vitamin C catches the oxygen hit during bottling. For the barrel I keep the non-dripping sulphur wicks ready, precisely because they don't drip, so they burn evenly and leave no glowing drop on the wood. Both are cheap insurance against an expensive total loss. My twenty litres of Riesling from 1998 would have lasted for years.
From the cellar, Magnus