Factors affecting the incidence of first-quality wheels of Trentingrana cheese

Trentingrana (or Grana Trentino) is a Protected Designation of Origin hard cheese produced in the eastern Italian Alps by small cooperative dairy factories. To obtain the certification of quality, wheels are evaluated at 9 +/- 1 mo of ripening and those classified as first quality are revaluated at 18 +/- 1 mo. Traditionally, the assessment is based on 2 sensory features: namely, the external aspect of the wheel and the internal texture; the latter is evaluated through the sound produced by beating the wheel with a special hammer. Traits considered in the study were the percentage of first-quality wheels of total wheels examined at 9 +/- 1 (QW(9mo)) and 18 +/- 1 (QW(18mo)) mo of ripening, and their combination [i.e., the percentage of first-quality wheels at 18 +/- 1 mo of ripening of the number of wheels evaluated at 9 +/- 1 mo (QW(tot))]. The experimental unit was the batch of 2 mo of production of each of 10 cooperative dairy factories from 2002 to 2008. Data were analyzed with a model that included fixed effects of dairy factory, year and season of production, and interactions between dairy factory and year, and dairy factory and season. The coefficients of determination of the models were 0.57, 0.68, and 0.67 for QW(9mo), QW(18mo), and QW(tot), respectively. All factors significantly influenced the traits, with dairy factory being the most important source of variation, followed by season and year of production. Remarkable differences were found between the best and the worst dairy factory for QW(9mo) (11.5%), QW(18mo) (21.1%), and QW(tot) (25.6%). The first 4 yr of production had a negative effect on the percentage of wheels labeled as first quality and QW(tot) decreased from 74 to 64%; nevertheless, a complete recovery was detected in the following years. The season of production strongly influenced the studied traits with the best results in spring and summer, and the worst in autumn and winter. Compared with average, the 3 best dairy factories were smaller, with smaller associated farms, and showed lower variation across years and seasons of production. Results support the relevance of routinely assessing and monitoring the quality of Trentingrana cheese.