In the autumn of 1987 I sugared my first apple wine by ear. My neighbour reckoned half a pound per litre always fits. It didn't. The yeast gave up, exasperated, somewhere beyond 14 percent by volume, a sticky residual sweetness stood in the demijohn, and what I racked in spring was no apple wine but a tired liqueur blend. Since then one simple sentence has applied in my cellar: measure first, then pour.
Four instruments haunt home winemaking: the Oechsle hydrometer, the vinometer, the acidometer and the alcoholometer. Two of them you really need, one is optional, and one belongs in the distillery and nowhere else. In order.
The Oechsle hydrometer: measuring sugar before anything ferments
The Oechsle hydrometer is a floating hydrometer. It measures how much heavier your juice is than water. A litre of water weighs 1,000 grams; if the hydrometer shows 80 °Oechsle, the litre of must weighs 1,080 grams. This extra weight is for the most part sugar, and out of sugar the yeast makes alcohol: roughly 16 to 17 grams of sugar per litre give about 1 percent by volume. As a rough rule of thumb you can divide the must weight by eight, then you have the possible alcohol. More precise are the tables that come with every instrument's instructions and that also stand in the Kitzinger Wine Book, which was printed in more than 750,000 copies and has answered exactly such questions for generations.
This is how you measure cleanly:
- Pass the juice through a fine sieve. Fruit pulp and coarse sediment fake a density that isn't sugar.
- Fill the measuring cylinder (250 ml) to about three quarters.
- Immerse the hydrometer with a slight spin, so that clinging air bubbles are shaken off. Bubbles carry the hydrometer and falsify upwards.
- Read off at eye level at the surface of the liquid.
- Check the temperature: the scale is calibrated to 20 °C. Cold must reads too high, warm too low. So temper it or correct.
During fermentation the readings are to be treated with caution, because the rising carbon dioxide lifts the hydrometer. If you want to follow the course of fermentation, stir the sample and wait until the bubbles are out. And don't be surprised if a fully fermented wine reads below zero: alcohol is lighter than water, the hydrometer sinks deeper than in pure water. That's no defect, that's physics.
The vinometer: measuring alcohol when it's all over
The vinometer is a capillary tube with a funnel. You put a few drops of wine in, let them run through until a drop hangs at the bottom, turn the device over and read where the sinking column comes to rest: alcohol in percent by volume, accurate to about half a percent. Behind it is surface tension, and unfortunately that changes not only with the alcohol.
Hence the iron rule: only fully fermented, still wines. Residual sweetness drives the reading up; a stopped, sweetish wine delivers fantasy figures. Carbon dioxide also interferes, so swirl the sample vigorously beforehand. With a dry, clear wine you get, in exchange, a figure within a minute that is quite enough for the cellar log and the label.
The acidometer: acid is the character of your wine
Sugar you can taste. Acid you can only estimate badly, because sugar masks it; a sweet must tastes milder than it is. The acidometer determines the total acidity by titration: a measured amount of must or wine into the measuring vessel, add the blue titration lye drop by drop as per the pack instructions, read off the total acidity in grams per litre at the colour change. That sounds like chemistry class but takes less than five minutes.
As a rule of thumb I set fruit musts to about 6 to 8 grams per litre. The fruits themselves keep to no norm: blackcurrants easily bring over 20 grams per litre and have to be stretched with water and sugar. Pears often drift below 3 and need an acid addition, otherwise the wine turns bland and, on top of that, prone to germs, because acid preserves. After every dilution or acidification you measure again. In 1998 I once skipped that; the acetic spoilage that came of it reeks, in my memory, to this day.
The alcoholometer: only for distillates
The alcoholometer looks confusingly similar to the Oechsle hydrometer, and precisely therein lies the misfortune. It's a floating hydrometer, calibrated for pure water-alcohol mixtures. Wine is no such mixture: sugar, acids, glycerol and extract carry the hydrometer and push the reading far below the true value. A wine with 12 percent by volume can look there like almost nothing. In a clear distillate, on the other hand, the device measures exactly, that's what it's built for. In short: whoever doesn't distil needs none.
What you can spare yourself
- Refractometer: only reads honestly in unfermented juice. As soon as alcohol is involved, you need correction formulas. For a few batches a year the hydrometer will do.
- pH meter: pH value and total acidity are two different things. For fruit wine in the hobby cellar, total acidity is the decisive figure.
- Vinometer: optional, not mandatory. Whoever notes the start and end Oechsle knows their alcohol pretty exactly anyway.
- Alcoholometer: see above. Distillery, nothing else.
The measuring schedule
- Before setting up: measure must weight and total acidity. Only then calculate water and sugar.
- After sugaring: control measurement with the Oechsle hydrometer, value into the cellar log.
- During fermentation: watch the airlock, at most follow the Oechsle course. The vinometer stays in the drawer.
- When the airlock is quiet for days and the hydrometer reads around or below zero: fully fermented. Now the vinometer may come out.
- Before racking and sweetening: check the acid once more and taste. The glass is part of measuring technique too.
The classics among these devices come, by the way, from Kitzingen: the Arauner company, founded in 1897 by the pharmacist Paul Arauner, taught generations of hobby winemakers to measure, before the business ended in May 2024. We carry on the remaining original devices and the knowledge that goes with them from Aachen.
Two honest notes on the tools: for the must I take the Oechsle hydrometer with thermometer, because I see the temperature directly at the sample and don't first have to bring everything to 20 °C; whoever patiently tempers gets by with the version without thermometer too. For the acid I take the Acidometer complete set from Kitzinger, because the blue lye comes with it and you need nothing else. A vinometer is a nice extra, an alcoholometer you leave lying, as long as you don't distil.
From the cellar, Magnus