Proline content of grapes and wines

The proline, ammonia and total nitrogen content of some California grapes and the praline, total free amino acids and total nitrogen of the wines have been measured. The juice contains the predominant amount of the proline (50 to 80 %) in the grape cluster ; while the skins and seeds contain in excess of 50 % of the total nitrogen. Very little proline is found in the stems. A moderate portion is in the pulp (5 to 20 %). The praline can make up from 5 to 43 % of the total nitrogen in the juice depending o n vari ety and on grape m aturity. The Cabernet family of grapes appears to have highest percentages of prnline. A large percentage of the total amino acid left in the wine is in the form of proline. The amount of proline in the wine can vary from O to about 90 % of the total nitrogen. The wines with larger amounts of total nitrogen have higher percentages of residual proline. Rootstock affects the amount of total nitrogen but does not appear to affect the ratio of proline to total nitrogen. Th e ranges found in California grape juices range from 304 to 4600 mg/l of proline and in the wines from O to 3400 mg/l of proline. The average proline value for 78 juices was calculated as 742 mg/l and for the tabul ated data of 42 wines (from mainly cool climate grapes) - one half fermented on the skins the other half not - an average value of 869 mg/l of proline was found