The addition of nutrient supplements to grape juice prior to/during fermentation can now be managed accurately in terms of Yeast Available Nitrogen (YAN). YAN is especially important to determine accurately, as too little available nitrogen can result in sluggish or “stuck” fermentation and the generation of hydrogen sulphide (H2S) gas, while too much nitrogen, such as in the form of added diammonium phosphate (DAP), can lead to the formation of the carcinogenic compound ethyl carbamate, especially where starting levels of L-arginine in the juice are high.
The PAN assay procedure (K-PANOPA) described in this booklet is a more accurate alternative to formol titration that also measures proline, an abundant amino acid found in grape juice that does not contribute to YAN in anaerobic fermentations.