The Test That Reads Whether Wine’s Sugar Came from Grapes or a Sack

By the This Day in Wine History Editorial Team · Researched, fact-checked & verified by the TDIWH Editorial Team.

There is a kind of wine fraud no taster can catch: quietly adding sugar before fermentation so a thin wine ferments to a fuller, stronger one. The extra alcohol tastes like any other. But in 1981, two French chemists found a way to read the wine’s own molecules and tell whether that sugar began life as grapes — or came out of a sack of beet or cane. The method does molecular bookkeeping in an element most people never think about: heavy hydrogen.

The fraud you can’t taste

Chaptalization — adding sugar to the grape juice before or during fermentation — is legal and normal in some cool regions and years, where it helps under-ripe grapes reach a sensible alcohol level. But do it secretly, or beyond what the rules allow, and it becomes fraud: you are selling watered-down or over-cropped wine dressed up as something riper and more valuable. The giveaway would have to be in the finished wine, and the finished wine tastes like wine. The added alcohol is chemically the same drink.

So the question became almost forensic. Once the sugar has fermented into alcohol and the evidence has, in effect, been drunk by the yeast, is there any trace left of where that sugar came from? The surprising answer is yes — written into the atoms of the alcohol itself.

The taster asks whether the wine is good. The molecule answers a different question: whether it is honest.

Deuterium bookkeeping

In 1981, Gérard and Maryvonne Martin, a husband-and-wife research team at the University of Nantes in France, developed a technique with a mouthful of a name: Site-specific Natural Isotope Fractionation studied by Nuclear Magnetic Resonance — SNIF-NMR for short. Its trick is to look at deuterium, the rare “heavy” form of hydrogen, and measure exactly how it is distributed across the different positions in a molecule of ethanol.

That distribution is not random. A plant lays down a subtly different pattern of heavy hydrogen in its sugars depending on how it photosynthesizes and where it grew, and fermentation carries that pattern into the alcohol. So the wine’s alcohol keeps a faint fingerprint of the sugar it came from. The key division is between so-called C3 plants — which include both grapes and sugar beet — and C4 plants like sugar cane and corn. A companion carbon-isotope test cleanly catches cane or corn sugar; beet sugar, chemically closer to grape, is the one that the deuterium fingerprint is needed to expose. Together they leave added sugar with nowhere to hide.

It is worth being precise about what the method proves. It does not photograph the crime. It compares the wine’s isotope readings against reference ranges built from genuine wines of known region and vintage — a databank of the real thing — and flags values that fall outside what honest grapes could produce. That is powerful evidence, not a confession, but it is evidence no amount of skillful blending can talk its way out of.

From a lab in Nantes to the law

The method did not stay an academic curiosity. In 1987 the Martins’ son, Gilles, founded the company Eurofins to commercialize it, and by 1990 the European Commission had adopted SNIF-NMR as an official way to detect beet or cane sugar added to wine. It sits today among the reference methods of the OIV, the international wine body, usually paired with related isotope tests that also catch watering.

The result is a quiet revolution in trust. For most of wine’s history, the only defense against a doctored bottle was a discerning palate — and palates can be fooled. Now a regulator can pour a sample into a spectrometer and read, in the ratios of heavy hydrogen, a truth the winemaker never meant to record. The taster asks whether the wine is good. The molecule answers a different question: whether it is honest.

This day in wine history

• 1981 — Gérard and Maryvonne Martin develop SNIF-NMR at the University of Nantes.
• 1987 — Eurofins is founded to commercialize the method.
• 1990 — The European Commission adopts SNIF-NMR as an official test for added beet or cane sugar in wine.

Frequently asked questions

Read more

Explore more of wine’s long fight against fraud in our history of wine fraud, or browse our Turning Points in Wine History collection.

Further reading

As an Amazon Associate, This Day in Wine History earns from qualifying purchases. Book links are affiliate links; cover images are used for identification.

Wine Science: Principles and Applications
Ronald S. Jackson
Comprehensive textbook covering grape chemistry, fermentation, and methods to authenticate wine.

Understanding Wine Chemistry
Andrew L. Waterhouse et al.
Guide to wine’s molecules, including isotopic markers that reveal added sugar.

Sources

1. OIV, official method for the determination of the deuterium D/H ratio in wine ethanol (SNIF-NMR), Resolution OIV-OENO 426-2011 — the official method. oiv.int
2. N. Christoph, A. Hermann & H. Wachter, “25 Years authentication of wine with stable isotope analysis in the European Union,” BIO Web of Conferences 5 (2015) — the EU regulatory history. doi.org
3. G. J. Martin & M. L. Martin, “Deuterium labelling at the natural abundance level…,” Tetrahedron Letters 22 (1981) — the foundational paper. doi.org
4. Eurofins, “The SNIF-NMR Concept” and “How it all began” — the originators’ account of the method and its commercialization. eurofins.com
5. OIV, method for carbon-13/12 (IRMS) detection of C4 sugars, OIV-MA-AS312-06 — the companion isotope method. oiv.int

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