Jeffrey Maccario,* Benjamin Ayer, Josh Freese, and Richard DeScenzo
*ETS Laboratories, ETS Laboratories, 899 Adams St, Saint Helena, CA, 94574 (jmaccario@etslabs.com)

The 2022 and 2023 vintages presented Vitis vinifera juice samples with unexplained loss of malic acid prior to the onset of primary fermentation. These fresh juices, lacking malic acid, contained no detectable lactic acid bacteria (LAB) by common PCR and plating methods. Culture plating from these juices and 16S rDNA sequencing identified the predominant bacterium present as Tatumella ptyseos.

Prior research on vineyard microbiomes using NextGen sequencing indicates several Tatumella species are commonly associated with winegrapes. The presence of this rod-shaped, gram-negative, facultative, and anaerobic bacterium was associated with lowered acidity in the juice. The authors of the papers did not report on changes in specific acid components of the juice.

Initial experiments indicated the cause of lowered acidity associated with T. ptyseos in grape juice was due to rapid depletion of malic acid. Additional experiments were done to characterize the growth of T. ptyseos under standard winemaking conditions.  These experiments evaluated growth rate, malic acid and sugar consumption, acid production, and tolerance to ethanol, temperature, and sulfur dioxide.

This is the first report confirming the ability of T. ptyseos to metabolize malic acid, resulting in a lower juice acidity.

Funding Support: ETS Laboratories