Degree Oechsle
Unit outside the SI · quantity: the sugar content of grape juice expressed through density · one degree equals one gram by which a litre of juice is heavier than a litre of water
Ferdinand Oechsle kept a workshop of precision balances in Pforzheim and, like every south German townsman of his day, had dealings with wine, which was bought by eye and by tongue: the sweetness of the juice was judged by dipping a finger, and then argued about all winter. In the early thirties he proposed weighing not the tongue but the juice itself, and did it in the cheapest way — he dropped a float into a measuring cylinder and wrote on its scale not the density but the difference: how many grams extra a litre of juice weighs against a litre of water. The number came out convenient to the point of indecency, because almost everything extra in a grape is sugar.
From this everything else follows: a hundred degrees Oechsle mean that a litre of must weighs 1100 grams, and that this juice will make a wine of about twelve and a half per cent, since sugar turns into alcohol after fermentation in a known ratio. The German wine law built a whole ladder of titles on this scale — Kabinett, Spätlese, Auslese — so the figure off the float settles not only the taste but the price of the bottle, and that is why in September it is taken in the vineyard every morning.
How much extra a litre of juice weighs
The definition rests on a single subtraction: the density of a sample of must is measured at twenty degrees Celsius, divided by the density of water at the same temperature, one is taken away from the ratio obtained, and the difference is multiplied by a thousand. A must of density 1.085 g/cm³ thus gives eighty-five degrees Oechsle, and the whole scale is nothing but the third and fourth digits of the density brought forward, so that they can be read conveniently and said aloud.
Sugar is not measured at all here — it is inferred. Besides it, the juice holds dissolved acids, mineral salts and pectins, which together make about two grams per hundred, and this correction sits inside every conversion table. Since the share of non-sugars varies little in healthy grapes, the substitution proves harmless; but let the berry fall ill or the juice begin to ferment, and the float starts to lie, because glycerol is heavier than water and alcohol lighter, and both shift the density their own way.
The reading of the float is made up of everything dissolved and not of sugar alone, and so the very first day of fermentation devalues the instrument: alcohol is lighter than water, and the density falls faster than the sugar diminishes. A hydrometer in a fermenting vat shows figures that mean neither sugar content nor strength, only the balance of two opposite shifts, and the trade has invented a separate name for them — apparent density.
Hence the rule of the cellar: degrees Oechsle measure the juice before it is set to ferment, and after that one passes to other ways — reckoning the alcohol by distillation, or taking a refractometer reading together with the density and solving a system of two equations. The quantity itself remains a measure of one instant: that morning when the grapes came off the vine.
Until the middle of October the sugar content rises because the leaf drives glucose into the berry, and this growth is honest: there is as much juice in the bunch as before, and more sugar in it. Later the vine falls still, yet the number on the float goes on climbing — now because the berry is losing water, and the sugar simply ceases to be diluted.
That difference matters more than it seems, for on it depends how much wine a hectare will give: the concentration rises while the volume falls, and two hundred degrees Oechsle in a nobly moulded berry mean not a rich harvest but a few bottles off a whole row. The acidity meanwhile falls in both cases, and it is its fall, not the rise of sugar, that usually decides that the grapes are to be picked.
One sample, four national scales
All four scales read one and the same density, but each writes it in its own way: Oechsle leaves the grams per litre, Brix converts them into per cent by mass, Klosterneuburg subtracts the non-sugars and therefore gives figures five times smaller, and Baumé keeps the old hydrometer graduation, in which one degree answers to about eighteen grams of sugar. To argue which is the right one is pointless — all that matters is not to mix them in a single report.
At the bottom of the scale all the conversions share one weakness: below fifty degrees Oechsle the juice is rarely grape juice at all, and above two hundred and fifty the float ceases to swim in the thick syrup, and there one measures with a refractometer instead. Both limits stand not in the law but in the make of the instrument.
The whole scale fits into two hundred degrees
The Oechsle scale is a rarity in this catalogue: it need not be run on a logarithm, because the whole world of the grape fits between fifty and two hundred and fifty degrees, and everything else is either not juice or no longer wine. The pale band marks the region in which the German ladder of titles works.
What the sugar content is taken with
A glass float with shot in its belly and a scale on its stem: where the meniscus crosses the graduation, there is the degree. The instrument wants half a litre of juice, a level stand and patience, but it does not break and costs less than the sample of grapes floating in it.
Two drops are enough: the beam is refracted in the juice, and the boundary of light on the scale gives the dry substance in degrees Brix, whence a table converts it into Oechsle. Growers walk the rows with it a week before the harvest, because it reads every bunch separately.
The arbitration method: a flask of known volume is weighed empty, with water and with must, and the density comes out of the two ratios. Slow, but free of corrections for the shape of the meniscus — it is on this instrument that floats are certified.
The modern receiving station: a tube with the sample is set swinging, and the density is found to the sixth digit from the frequency of its own oscillation. Two millilitres and ten seconds are enough, and the thermostat inside removes the question of correction.
How to write it and how not to
The nearest kin
The mass fraction of dry substance in per cent: the same grams, referred to a hundred grams of juice and not to a litre. The common measure of the food industry, and therefore a grower who has bought a refractometer on the internet almost always gets a Brix scale and converts it into Oechsle by a table.
The Austrian measure, in which the non-sugars are subtracted beforehand, so that the number comes out nearly five times smaller and already means honest per cent of sugar by mass. The conversion between it and Oechsle is quadratic, and hence the tables of the two countries do not meet by a linear factor.
The old hydrometer scale, surviving in France and Australia, where it is valued because the number nearly coincides with the future strength of the wine in per cent. Twelve degrees Baumé — twelve turns, and in conversation that is handier than any conversion.
How a float became a legal document
Ferdinand Oechsle, mechanic and assayer of gold at Pforzheim, brings out his beam balance with a scale carrying not the density but the excess over water. The choice proved decisive: the figures came out large and whole, so that they could be called across a yard without confusion over decimal places.
At Klosterneuburg near Vienna, Baron August Wilhelm von Babo, who founded the first school of viticulture there, introduces a scale of his own: from the density reading he subtracts the acids and salts in advance, so that the number should mean per cent of sugar directly. The Danube empire fell apart, and the two scales on either side of the former border remained.
The German wine law abolishes the old muddle of vineyard names and builds its classification on one measurable figure — the sugar content of the must. Kabinett, Spätlese and Auslese become not a description of the picking but thresholds of the Oechsle scale, and from that day the reading of the float acquires the force of a document.
The warm decades did what the lawgiver had not thought of: thresholds that once were reached every few years came to be reached almost every autumn, and Spätlese ceased to be a distinction. Growers began to pick earlier — not for the sugar but to keep the acid, without which Riesling loses its edge.
The unit measures something other than it names, and everyone is content
The degree Oechsle is called sugar content, though it does not see sugar: the float feels every dissolved weight, and in its reading the acids, salts and pectins sit together with the sugar. The substitution holds because in a healthy berry the share of non-sugars is nearly constant, so that one number reliably predicts the other — and it holds exactly as long as the grapes are healthy.
Let the berry dry a little or take on noble rot, and the tie falls apart: the fungus eats part of the sugar, leaving glycerol, which is heavier than water and therefore duly lifts the float, promising the wine a strength that will not be in it. Hence in the dearest categories, where the degrees run past two hundred, the reading is checked not with a float but with a chromatograph — an instrument devised for cheap honesty proved powerless exactly where the money is large.