# Quality Assessment of Organic Kefirs Made with Kefir Grains and Freeze-Dried Starter Cultures
## 1 Introduction  
Organic food, otherwise known as BIO food, refers to products derived from organic raw materials. Organic dairy products are made from milk sourced from certified organic farms that adhere to strict requirements regarding the nutrition, maintenance, and treatment of dairy animals. Organic milk processing involves the highest standards of quality and safety [1]. European Union regulations, mainly Regulation (EU) 2018/848 of the European Parliament and of the Council [2], define the rules for the production, labeling, and inspection of organic products. Organic dairy products are gaining popularity among consumers. This trend is driven by the fact that, when making a purchasing decision, consumers are increasingly guided by environmental considerations (such as sustainability in farming) and animal welfare [3, 4]. Another factor influencing the choice of organic dairy products is the assurance that they are free from residues of artificial fertilizers and pesticides, antibiotics, and hormones, which are prohibited in organic production. Consumers are also guided by the conviction that organic milk is superior in many ways to conventional milk. Those are the reasons why consumers usually choose the more expensive organic products [4, 5, 6]. Due to differences in organic and conventional milk processing, the resulting products may differ in terms of quality characteristics. These variations are a result of different feeding and animal housing conditions on organic farms compared with a conventional one [5, 6, 7, 8]. Organic milk is characterized by a more favorable fatty acid profile than conventional milk. It has a higher concentration of beneficial fatty acids (FA) including n-3 polyunsaturated fatty acids (n-3 PUFA) [9; 10; 11], conjugated linoleic acid (CLA) [12; 13; 14; 15], and \(\alpha\)-linolenic acid [13; 16]. Other studies have demonstrated higher concentrations of fat-soluble vitamins tocopherol and \(\beta\)-carotene in organic than conventional milk [12; 14; 17]. Moreover, organic milk has a higher concentration of such bioactive compounds as lactoferrin [18; 19], lysozyme [18; 19], and phospholipids [15] than conventional milk. In case of proximate chemical composition of organic milk, many studies indicate a lower protein and casein content compared with conventional milk [11; 19; 20; 21; 22]. It is likely caused by a lower amount of concentrated feed starch in the nutrition of organic dairy cattle [20]. In the case of fat content, a meta-analysis conducted by [PERSON] et al. [23] found no significant difference between milk from organic and conventional farming. The literature presents contradictory results regarding lactose content, which may be similar [4] or lower [16; 20; 24] in organic milk compared with conventional milk. The mineral content is lower in organic milk, as conventional farming allows for mineral supplementation in concentrated feed [4; 18; 25]. However, conventional milk tends to be more contaminated with heavy metals [4; 26]. In terms of sensory quality, organic and conventional milk were compared by [PERSON] et al. [27]. The study indicated a positive consumer perception and full acceptance of organic milk. Conversely, a study conducted by [PERSON] et al. [28] showed that organic milk from grazing cows was creamier and had a stronger grassy flavor compared with conventional milk from cows kept in barns. The differences in the composition of organic and conventional milk, especially the higher concentration of long-chain PUFA and bioactive compounds in organic milk, make it a better medium for lactic acid bacteria (LAB) growth. Thus, organic milk appears to be a better raw material for fermented beverage production such as kefir and yogurt than its conventional counterpart [25]. Kefir is a type of fermented dairy beverage in which LAB conducting lactic acid fermentation as well as yeasts conducting alcoholic fermentation are involved [29].