Probiotic yeasts are increasingly proposed as adjuncts in fermented dairy products, but their behavior in kefir is still poorly described. This proof-of-concept study examined the effect of Saccharomyces boulardii CNCM I-745 supplementation on kefir produced with two traditional grain cultures and two industrial direct-vat-inoculation cultures during 21 days of cold storage at 4 °C. Microbiological, physicochemical, and sensory parameters were monitored on days 1, 7, 14, and 21. The starter culture type was the main source of variation, with traditional grain kefirs showing higher microbial counts and better sensory scores than industrial cultures. S. boulardii did not change pH, titratable acidity, Lactococcus spp., or total mesophilic aerobic bacteria, indicating that it can be added without disturbing the established kefir microbiota or its acidification pattern. The probiotic yeast increased the total yeast count, slightly modulated Lactobacillus spp., and gave a small improvement in taste–aroma scores. In the yeast-free industrial culture, S. boulardii maintained viable counts above 6 log CFU/g throughout storage, showing that it can act as the sole yeast source in kefir matrices that lack indigenous yeast. Traditional grain kefirs kept a more stable overall sensory quality across 21 days than industrial cultures. The multivariate analysis confirmed two largely independent quality dimensions, one related to lactic acid bacteria and acidity and another to sensory perception. The study supports the use of S. boulardii as a probiotic adjunct in kefir and provides preliminary effect-size information for future, adequately replicated trials.

Gelveri Ekmeği hiçbir katkı kullanılmadan; tam buğday unu, maya, tuz ve sudan üretilmektedir. Gelveri Ekmeğinde mayalama ekşi hamurla sağlanmaktadır. Ekşi hamur kültüründe bulunan Lactobacillus spp. çok miktarda laktik asit ve asetik asit üretmektedir. Bu da ekşi hamur ekmeğine kendine özgü lezzet vermektedir. Gelveri Ekmeği coğrafi işaret ile tescillenmiştir. Güzelyurt Kapadokya Bölgesi’nin karakteristik çizgilerini taşır. Bunun en önemli belirtisi ise kaya oluşumları ile dolu olmasıdır. Kayalardan yapılmış fırınlarda asırlardır yapılan Gelveri Ekmeği yöre halkının hâlâ devam ettirdiği geleneklerden biridir. Güzelyurt ve çevre ilçelerde de tanınan Gelveri Ekmeği dayanıklılığı ile bilinmektedir.

Kefir is a self-carbonated fermented milk produced with kefir grains which is valued for its complex symbiotic microbiota and probiotic potential. Flavouring kefir is a recognised strategy to broaden consumer appeal, yet the moment at which a flavouring ingredient is introduced—before or after fermentation—may differentially affect the product. The present study evaluated the effect of the timing of instant coffee addition on the physicochemical, microbiological and sensory properties of kefir during 14 days of refrigerated storage (4 ± 1 °C). Three kefir samples were produced from UHT cow’s milk (3% fat) inoculated with 3% (w/v) kefir grains: a control without coffee (K), kefir with 0.5% (w/v) instant coffee added before fermentation (PreF_CK) and kefir with 0.5% (w/v) instant coffee added after fermentation and maturation (PostF_CK). Samples were analysed on days 1, 7 and 14. The coffee addition significantly increased the total dry matter (K = 10.72%; PreF_CK = 11.04%; PostF_CK = 11.00%; p < 0.01) and slightly modified the titratable acidity and pH (p < 0.05), whereas the ash content (expressed in terms of dry matter) did not differ among samples (p > 0.05). The titratable acidity increased and the pH decreased with storage in all samples (p < 0.05). Crucially, the coffee addition—irrespective of the timing—did not impair the viability of the kefir microbiota; the total mesophilic aerobic bacteria, Lactobacillus spp., mesophilic lactic cocci and yeast counts did not differ significantly among the samples (p > 0.05) and remained high throughout storage (lactic acid bacteria ≥8 log CFU/g; yeast ≥5.7 log CFU/g), exceeding the minimum thresholds of the standards for fermented milk products. Sensory evaluation showed that the control achieved the highest odour and taste scores (p < 0.001), while among the coffee-containing samples, the post-fermentation addition (PostF_CK) was generally scored at least as high as the pre-fermentation addition (PreF_CK); overall acceptability did not differ significantly among the samples (p > 0.05). These findings demonstrate that 0.5% instant coffee can be incorporated into kefir without compromising its characteristic microbiota or storage stability and that post-fermentation addition is a viable route for producing an acceptable coffee-flavoured kefir.