The high solids content of sheep milk makes it a natural for production of premium yogurt products similar to the Greek-style yogurt. With solids content of 16 18% in the milk, yogurts can be produced without the need for added milk solids or stabilizers. With the higher fat in sheep yogurt, the potential harshness of the lactic acid in the yogurt may also be lessened. The nutrient content of sheep yogurt is about 50% higher than cow milk yogurt.
Sheep milk for yogurt production should be pasteurized at 91 °C for 30 seconds or 82°C for 30 minutes. After cooling to 42 44°C, the milk is inoculated with Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus cultures. For set-type yogurt, the inoculated milk mixture is dispensed into cups and allowed to ferment at 44°C until the pH reaches 4.6. The yogurt is then cooled to 4°C and then stored at refrigeration temperatures until consumed. Probiotic cultures of Lactobacillus acidophilus or Bifidobacterium may also be added to the yogurt to improve the nutritional properties of the yogurt product. Very little sheep yogurt is produced by the stirred-type yogurt process.
Sheep yogurt exhibits a stronger structure to the yogurt gel and has less serum separation on storage than cow or goat yogurt. Viscosity of the yogurt could be significantly increased and serum separation decreased with homogenization of the milk prior to inoculation. Yogurt from sheep milk was reported to have twice the lactase activity of cow milk yogurt. Yogurts produced from milk pasteurized at higher temperatures tended to have a decreased rate of acid development and an increased rate of lipolysis.
Since sheep milk production is seasonal, use of frozen milk may be necessary to produce yogurt throughout the year. Good quality yogurt can be produced from frozen sheep milk if the milk is frozen and stored at — 27°C or less for less than 12 months. Seasonal variations in milk composition may impact the overall quality of the yogurt as the lactobacilli used in yogurt fermentations are sensitive to changes in milk composition.
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