# Quality Assessment of Organic Kefirs Made with Kefir Grains and Freeze-Dried Starter Cultures
## 1 Introduction
Kefir is an acidified, slightly carbonated fermented milk containing small amounts of ethyl alcohol with specific flavor typical of yeasts [30; 31]. Kefir originates from the Caucas Mountains, but it is now gaining popularity throughout the world [31; 32]. Traditionally, in kefir production, a starter culture in the form of kefir grains (KGs) is used. KGs are conglomerates of symbiotic microorganisms immobilized in a natural matrix of exopolysaccharide achefirand proteins. The size of kefir grains ranges from 1 to 4 cm, they are irregular in shape, are white to light yellow in color, and resemble small cauliflower florets [32; 33]. They are added to milk in a ratio of 2 to 10%, and after fermentation, they are removed from kefir and may be re-used [34; 35]. The predominant microbiota of KGs includes homoformetative and heterofermetative LAB belonging to the _Lactobacillus_, _Lactococcus_, _Leuconostoc_, and _Streptococcus_ species, as well as acetic acid bacteria (AAB) of the _Acetobacter_ genus, and yeasts, primarily _Saccharomyces cerevisiae_, _Candida kefirv_, _Kluyveromyces marxianus_, _Torulaspora delbrueckii_, and _Kazchastania unispora_[31; 32; 36; 37]. The wide diversity of microorganisms present in traditional kefir allows it to be considered as a natural probiotic product [35; 38]. LAB strains found in traditional kefir produce organic acids, bacteriocins, and hydrogen peroxide which are antimicrobial agents and inhibit the growth of pathogens [38; 39; 40]. Kefir also exhibits immune-modulating activity and has anti-cancer, anti-hypertensive, and calcium-binding properties, all of which contribute to its health-promoting and therapeutic effects [29; 30; 33; 41]. Moreover, kefir consumption is effective in preventing and treating obesity and metabolic disorders such as diabetes [42; 43; 44]. Its consumption is recommended during periods of convalescence or anemia [31; 33]. Additionally, it has a beneficial effect on digestion, improves lactose digestibility, and may influence plasma glucose levels [31; 33]. In industrial-scale kefir production, KGs are rarely used due to their complex application and the variability in kefir properties. Instead, commercial freeze-dried cultures, which contain selected species of LAB and yeasts in fixed proportions are often used. This kind of culture is easier to use and provides standardization of kefir quality. However, it is characterized by lower species diversity resulting in kefir with properties that differ from those produced with KGs, particularly in terms of reduced therapeutic benefits [30; 32; 38; 41]. Traditional processing methods, like the production of kefir with KGs, are typically more time-consuming and labor-intensive than modern methods [1]. However, in organic food processing, traditional production methods are preferred [2], making the use of KGs desirable for organic kefir production. The aim of this study was to analyze the quality characteristics of kefir obtained from organic cow milk using traditional kefir grains or freeze-dried cultures as a starter. The fermentation of kefir was conducted for a period of 12 or 24 h. The obtained products were refrigerated and stored for a period of 21 days. This article is an expanded version of the abstract published in the Book of Abstracts of The 5 th International Electronic Conference on Foods, held online from 28 October to 30 October 2024 ([[https://pub.epsilon.slu.se/35636/1/kravchenko-o-et-al-20241108.pdf](https://pub.epsilon.slu.se/35636/1/kravchenko-o-et-al-20241108.pdf)]([https://pub.epsilon.slu.se/35636/1/kravchenko-o-et-al-20241108.pdf](https://pub.epsilon.slu.se/35636/1/kravchenko-o-et-al-20241108.pdf)), accessed on 2 December 2024).