Humans already depend on microorganisms like yeast and lactic acid bacteria when making wine. It turns out that microbes may play a major role in how we taste wine too. Researchers in Spain have found that many of the aromatic compounds we smell while drinking wine wouldn't be detectable without the help of microbes that live inside our saliva.
Scientists are increasingly exploring the symbiotic relationship between humans and our microbiota, the millions of microorganisms inside us. Microbes in our digestive track may play a major role in our immune systems, for example. At least 700 bacterial species live in our saliva, on our teeth and on all the interior surfaces of our mouths.
For this study, sponsored by Spain's Institute of Food Science Research in Madrid and published in the journal Food Chemistry, a team wanted to determine how big a role those microbes play in the detection of aromatic compounds in wine. Grapes are full of chemical compounds called aromatic precursors, which are not necessarily detectable to our noses until their structures are changed by a chemical reaction. Vinification releases some of these aromas, while others are released by oxygen when you pour the wine in your glass.
But many don't emerge until the wine interacts with our mouths. Much of a wine's flavor is created by aromas we experience retronasally—we smell them as they rise to our noses through the back of the throat. The researchers wanted to know if oral microbes release these aromas.
In their first test, the team isolated nine of the most common types of bacteria found in our mouths, such as Staphylococcus aureus, Enterococcus faecalis and Streptococcus oralis. The scientists inoculated the bacteria cultures with a "wine grape aroma precursor extract" taken from Spanish Verdejo grapes, a fairly aromatic variety, and the various chemical compounds released upon interaction were measured by gas chromatography in order for the scientists to identify them.
Next, the team collected saliva samples from three healthy volunteers in order to test the entire microbiota of each mouth rather than just nine isolated bacteria. The samples were tested both aerobically and anaerobically, and the results were also measured with gas chromatography.
In both tests researchers found that the oral bacteria showed a strong ability to convert the grape aroma precursors, releasing many different types of aromatic molecules. That may explain why brushing your teeth right before enjoying a glass of wine will make the wine appear dull or off: You've just killed off a sizeable portion of the microbes in your mouth responsible for releasing aromas. The scientists found that E. faecalis and A. naeslundii were the workhorse bacteria, showing the greatest ability to produce aromatic compounds from non-aromatic precursors.
They also found a wide disparity of results among the samples harvested from the three volunteers, suggesting that each individual's microbiota impacted which aromas were strongest. Some possible explanations for these individual anomalies include heredity, environment, oral hygiene and diet—all of which could shape the population living in a subject’s mouth. María Victoria Moreno-Arribas, a coauthor of the study and a director at the Institute, told Wine Spectator, "This was the most interesting conclusion of our study—the fact that there is a huge individual component to all of this, that each individual's oral microbiota is as unique as human gut microbiota. These results warrant further studies."