Kefir (turski: "köpürmek" = "pjeniti se") - gusti tekući mliječni napitak, koji potječe s Kavkaza.
Mliječni kefir nastaje tako što se u kravlje, ovčje ili kozje mlijeko stave grumenčići kefira i ostave jedan do dva dana. Pri tome se mlijeko fermentira. Optimalna temperatura je od 10°C do 25°C. Sadržaj alkohola može varirati od 0,2 do maksimalno 2 stupnja. Masti i proteini odgovaraju sastavu mlijeka, koje se koristi. Takav kremasti napitak ima kiselkast ukus.
Grumenčići kefira mogu narasti kao orah ali nije neobično da budu veliki i kao šaka, gumene su konsistencije i sastoje se od proteina, masti i polisaharida, koje proizvode različite bakterije. Razmnožavaju se s vremenom i udvostruče masu za 14 dana. Suvišni grumenčići kefira mogu se sačuvati osušeni ili zamrznuti.
Za industrijski proizveden kefir obično se koriste hmelj i specijalno odabrane kulture bakterija koje ne odgovaraju kompleksnoj mikroflori prirodnog kefira. Drugi razlog zašto se ne koriste prirodni grumenčići kefira je što se pri skladištenju oslobađa ugljikov dioksid, što može izazvati eksploziju u pakiranju. Tradicionalni kefir sadrži mikrofloru koja se prilagođava sredini,te se mijenja s godišnjim dobima. Isključivo tradicionalno proizveden kefir od sviježeg mlijeka životinja na otvorenoj ispaši posjeduje ljekovita svojstva.
Od kefira se nadalje može prirediti i sir, te sladoled,a može ga se koristiti umjesto kvasca kod izrade dizanog tijesta, te kruha.
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A study on the protective activity of kefir against gastric ulcer.
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Kefir improves the efficacy and tolerability of triple therapy in eradicating Helicobacter pylori.
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