Seasonal variation in the composition of Irish manufacturing and retail milks. 1. Chemical composition and renneting properties.

Abstract

The composition and renneting properties of manufacturing and retail milk supplies were determined at 3-week intervals over a 12-month period. Three manufacturing and five retail milk plants were selected to represent different geographical regions within the country. Fat concentration in manufacturing milk was higher (P < 0.01) than in retail milk during both the outdoor grazing (June to October) and indoor feeding (December to March) periods (35.3 v. 33.6 g/kg and 34.7 v. 32.9 g/kg, respectively). Protein concentration of the milks was similar and increased from 30.8 g/kg during the indoor period to 33.2 g/kg during the outdoor period. Lactose concentration was higher (P < 0.001) in retail than in manufacturing milk during the indoor period (44.6 v. 43.8 g/kg) but was similar for both milks (44.4 g/kg) during the outdoor period. Rennet coagulation time and rate of curd aggregation of retail milk were greater (P<0.05) than those of manufacturing milk. Free fatty acid concentrations in retail milk were higher (P < 0.001) than in manufacturing milk during the outdoor period (11.1 v. 9.0 mmol/kg fat) and were similar but greater (13.4 mmol/kg fat) in both milks during the indoor period. Somatic cell counts in manufacturing milk were higher (P < 0.001) than in retail milk. Total solids and ash concentrations and freezing point of the milks were not different.