Beer is one of the oldest alcohol beverages and first records of its production date back to ancient time. The main ingredient was always some kind of cereal, which would undergo spontaneous fermentation when in contact with water and wild yeasts in the air. The addition of hops, an obligatory ingredient of beer today, started relatively recent: in the middle ages mixtures of herbs were used in beer prior to hops. Although hops conserves the beer in a certain way, and preserves it from spoiling, only modern pasteurization procedures can completely remove harmful microorganisms and prevent beer from spoiling. Tunnel pasteurization is process where packed beer is gradually heated, detained certain time at pasteurization temperature, and gradually cooled after that. Tunnel pasteurization is a very safe method of assuring sterile beer, but it is, however, the most expensive method. Flash pasteurization is less expensive and faster procedure where beer flows in a thin layer, gets quickly warmed up to pasteurization temperature and after pasteurization is loaded into sterile packaging. Microbiological analysis are taken during whole production process, as well both during and after pasteurization. Frequency of analysis depends on type of pasteurization. This work describes both pasteurization technologies in „Karlovačka pivovara/Heineken Hrvatska“, as well as plant sanitation and cleaning processes and microbiological analysis of beer obtained after pasteurization.