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Riesling: acidity, residual sugar and the question of petrol

Almost no white variety keeps this long or this reliably — and almost none is judged so often by the wrong marker on the label.

Last updated: 2026-07-26

Riesling is the white variety that explains what ageing potential is. Not because the wines are powerful — they are often light and low in alcohol — but because they carry two things that survive time: high acidity and, depending on style, residual sugar. Both preserve. A wine with sharp acidity and a low pH ages more slowly than a white twice its weight without that foundation.

Two axes: acidity and residual sugar

Acidity is the frame. It holds the wine together while the aromatics rebuild themselves over years, and it is why a Riesling can still taste fresh at twenty with the colour long gone dark. In the bottle it fades only slowly.

Residual sugar is the second axis, and it is routinely misread. It does not make a wine heavy; it makes it longer. It buffers the acidity, gives the fruit substance and pushes the ageing curve noticeably further out. A Kabinett with clear sweetness will usually outlast the same producer's dry estate wine, despite tasting lighter and costing less. Dismissing residual sugar as a beginner's category means underrating exactly the bottles in your own cellar that can wait the longest.

Keeping the styles apart

Two systems sit side by side, and they age differently.

Dry Riesling dominates in Austria and Alsace, and in Germany at the top end as Grosses Gewächs. Here the acidity carries the wine alone, supported by extract and alcohol. Such wines often feel severe when young, need a few years to broaden, and then move towards herbs, wax and dried stone fruit. In the Wachau, dry Riesling is the longest-lived wine the region makes.

The German Prädikat scale — Kabinett, Spätlese, Auslese, Beerenauslese, Eiswein, Trockenbeerenauslese — describes must weight at harvest, not necessarily sweetness in the glass. In practice it usually tracks rising residual sugar, and longevity rises with it. At the top the unit is no longer years but decades: a Trockenbeerenauslese is concentrated and acidic enough to outlive the person who bought it.

The ranges below are rules of thumb, not promises. Vintage, site and producer move them in both directions.

The petrol note

No other marker of maturity divides opinion so reliably. The reference is to a smell of paraffin, kerosene or warm wax that turns up regularly in mature Riesling. A single compound is responsible. It is not present as such in the grape but forms slowly in the bottle from precursors created when carotenoids break down, and it accumulates with the years rather than fading.

What encourages it is well documented: strong sun exposure on the bunches, water stress, high ripeness at harvest, warm vintages. The closure plays a part too — under screwcap, with very little oxygen ingress, the note usually shows more clearly than under cork. In wines grown cool and picked early it can stay in the background for years.

On timing, only a rough rule is possible: in a dry single-vineyard wine the note typically becomes noticeable from around five years on. If it appears in a two-year-old bottle, that is the vintage and the site talking rather than age — and no sign that the wine is mature.

As for why it polarises: in Australia, and in the Clare Valley in particular, it counts as a hallmark of the variety and is valued. In Germany many estates work in the vineyard specifically to hold it back, because in pronounced form it flattens everything else. Both positions are defensible. The note is not a fault, but it is dominant: once it displaces the fruit rather than accompanying it, little of a wine's origin is left. If you dislike it, drink your Rieslings earlier — deliberately, rather than by accident.

Too young, too old

Still too young: the acidity runs alongside the wine rather than through it. Dry single-vineyard bottlings feel narrow and hard, and the finish cuts off. In fruity-sweet wines the sweetness arrives in front of the fruit instead of behind it. Reductive, struck-match notes are common in young bottles and usually blow off within twenty minutes.

Past its point: the fruit moves from fresh to dried and finally to flat. The acidity remains — it is the last thing to go — and without fruit beside it, it reads as gaunt and angular. The colour deepens towards amber, which on its own says little: a twenty-year-old Kabinett is allowed to be dark and still taste alive. The finish is the better signal. Once it shortens and turns faintly bitter, the window has closed.

What to watch when laying it down

Riesling tolerates cold well, considerably better than most wines. A store that drops to eight degrees in winter does it no harm; it simply slows the wine down. Two other things it takes badly.

Temperature swings. Every cycle of expansion and contraction pumps a little air past the closure, and light wines low in alcohol are less protected against that than heavy ones. A room sitting constantly at sixteen degrees beats one swinging between eight and eighteen.

Light. Riesling traditionally comes in green or brown glass, but often in near-clear bottles as well, and white wine reacts more sensitively to UV than red. The mistake is rarely the cellar; it is the case standing in the kitchen for six months.

Two practical notes to close. With nobly sweet wines the half bottle is worth it for more than the price — once opened they keep in the fridge for weeks. And as with Grüner Veltliner, the only way to learn a fifteen-year curve is to have more than one bottle of it on the shelf.

Ageing estimates are rules of thumb, not guarantees. How long a given bottle carries depends on the vintage, the winemaking and above all on storage. When in doubt, open one bottle earlier than planned.