ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 18, 2010 ABSTRACT Flow properties of a selection of common Norwegian dairy products were tested by a rheological rotational method, changing the shear rate up and down between 0.01 and 200 s -1 . Herschel-Bulkley model fitted well to the downward curve. Samples proved to be plastic as indicated by high yield stress values. A marked hysteresis loop was observed on flow curves indicating strong time-dependent behavior of all the samples tested. INTRODUCTION Fermented dairy products have three main categories: cheese, yoghurt and fermented liquid milk .Today some of them have even probiotic effects. A required step in cheesemaking is separating the milk into solid curds and liquid whey. Usually this is done by acidifying (souring) the milk and adding rennet. The acidification can be accomplished directly by the addition of an acid like vinegar in a few cases (paneer, queso fresco), but usually starter bacteria are employed instead. These starter bacteria convert milk sugars into lactic acid. The same bacteria (and the enzymes they produce) also play a large role in the eventual flavor of aged cheeses. Most cheeses are made with starter bacteria from the Lactococci, Lactobacilli, or Streptococci families. Swiss starter cultures also include Propionibacterium shermanii, which produces carbon dioxide gas bubbles during aging, giving Swiss cheese or Emmental its holes. After curd formation the whey is removed. In Norway the whey is utilized as “whey cheese” or mysost 1, 2 . Yoghurt can be considered as a curdled milk product, made of pasteurized milk, by adding starter culture (Streptococcus thermophilus) and other ingredients if needed (flavor, sweetener, colorant, stabilizer, gum). Then the milk is incubated at 40°C for 3 hours, cooled down to 15- 20°C, and added live culture. Other forms of yoghurt as frozen or stirred yoghurt and yoghurt drinks are also available and popular products. Fat content, solids-not-fat, flavors and appearance are widely varied in different countries 3,4 . Sour milk products are the most basic fermented liquid milk products. Many variants are made of low fat milk, which is pasteurized and added starter culture (Bifidobacterium bifidum, Lactobacillus acidophilus, Bifidobacterium lactiscultur, Lactobacillus rhamnosus GG etc.). Then the nilk is fermented to pH 4.65-4.55, and cooled to 4-6°C. Sour milk products may not contain any stabilizer or gum and are considered a health food due to live cultures 3, 5 . Kefir is a fermented liquid milk product characterized by small amounts of alcohol. It contains its inoculant, the kefir grains. The processing technology consists of two main parts: preparation of mother kefir and preparation of drinkable kefir. For the first part pasteurized milk is added to the kefir Flow Properties of Common Norwegian Dairy Products Ildikó Csilla Zeke 1 , Réka Juhász 1 , Reidar Barfod Schüller 2 and Elling-Olav Rukke 2 1 Corvinus University of Budapest, Budapest, Hungary 2 Norwegian University of Life Sciences, Ås, Norway