There are some foods that never spoil – honey, white rice, sugar, dried beans and lentils, dry pasta, and even hard liquor like whisky, vodka, and rum. But wines do spoil, because of the buildup of acetic acid – the compound responsible for vinegar-like smells and sour flavors that is bottled and sold in supermarkets as white vinegar.
Once acetic acid levels rise, the fermentation process can stall, and the wine may become undrinkable. Existing techniques for measuring acetic acid rely on laboratory techniques such as gas chromatography and liquid chromatography, but these are expensive, slow, and require liquid samples. These limitations make it difficult for wineries to monitor fermentation in real time and react before damage is done.
Researchers at the Hebrew University of Jerusalem (HUJI) have built a living biosensor made of bacteria that lights up when it detects acetic acid. It works in real time, even in high-alcohol conditions, so wineries can catch problems early, before flavor and quality are damaged. This could potentially save wine producers and consumers from costly quality losses.
The approach could offer a simpler, lower-cost alternative to lab testing and strengthen quality control across fermentation-based industries, according to protein engineering and nanobiotechnology Prof. Oded Shoseyov – an inventor, scholar, and author who supervised the research at the university’s Robert H. Smith Faculty of Agriculture, Food and Environment. The research was led by HUJI doctoral student Yulia Melnik-Kesler, under the guidance of Prof. Yael Helman.
Shoseyov told The Jerusalem Post in an interview that he has always felt close to growing grapes and producing wine. His family has lived in the Land of Israel for eight generations, and even today, they have a 20-hectare vineyard at Karmei Yosef, a community settlement in the Judean foothills in central Israel, plus a successful winery. His favorite wines are Merlot (red grapes) and Sauvignon blanc (green-skinned grapes).
“Because the best wine is aged in wooden barrels to produce the best flavor and not in stainless-steel kegs, oxygen enters and the bacteria can produce acetic acid. This is not dangerous to health, but it affects the taste,” Shoseyov explained.
The study has just been published in the journal Microbial Biotechnology under the title “Detection of Spoilage-Associated Acetic Acid Levels Using a Transcription-Based Whole-Cell Biosensor.”
TO MEET this challenge, Helman’s team created a living biosensor made from engineered bacteria that glow in response to acetic acid. The system uses a natural bacterial regulator called YwbIR, which is originally found in Bacillus subtilis. This type of bacteria, also known as the “hay bacillus” or “grass bacillus,” is found in soil and the gastrointestinal tract of cud-chewing cows, sheep, humans, and marine sponges.
Once transcribed in the biosensor, it activates a light-producing gene. It forms biofilms through the formation of extracellular polymeric matrix containing sugars and proteins. When acetic acid is present, the biosensor emits a quantifiable luminescent signal to indicate the amount of the compound present.
One of the most important breakthroughs is that the sensor works not only in liquid, but also in the air above the wine. This means it can detect volatile acetic acid in the headspace of a wine bottle or fermentation tank without opening it. In tests with commercial red and white wines, the biosensor successfully distinguished normal wine from wine that had been artificially spoiled by adding acetic acid, producing a clear increase in light output within two hours.
In lab tests, the biosensor showed a strong and linear response to acetic acid levels between 0 and 1 gram per liter. This range is critical for winemakers, as spoilage typically begins when levels reach approximately 0.7 grams per liter. At these spoilage-relevant concentrations, the signal increased by five to eight times, providing a clear warning long before the wine becomes undrinkable.
Biosensors more reliable than electronic, optical sensors
Unlike many electronic or optical sensors, the new biosensor remains reliable even in high-alcohol environments. It functioned accurately in wines containing up to 14.5% alcohol – a condition that typically interferes with conventional detection systems. Beyond wine making, the researchers believe the technology could have much wider applications.
Shoseyov concluded that “acetic acid is an important indicator in many fermentation-based industries, including food production and biofuels. Since fruits and vegetables also produce acetic acid, their freshness can be monitored in warehouses with this technology.”
The benefits of this new technology may not be limited to food preservation. “Because humans also give off small amounts of acetic acid in their body odor as a natural byproduct of metabolism, particularly in the breakdown of fats and carbohydrates,” the professor said, “the technology could be used as a biomarker of certain diseases for noninvasive medical diagnostics.”