The gentle boiling process goes as follows: Pfannevoll volume is heated to 98°C in the existing copper or via external heating units. This is followed by hot holding 1°C below boiling temperature, either atmospherically or at a slight pressure. The duration of hot holding is dependent on analytically pre-selected parameters. It can take between 50 and 70 min. Hop additions are adapted to suit the conditions in the particular plant. Intensive convection is important during hot holding in order to achieve the desired changes in the wort. This is done in combined mash and wort coppers using the existing agitator, and by means of a circulation unit in wort coppers. "Evaporation" is between 0.3 - 1% depending on copper type. In recent tests, wort was cooled down to 75°C.
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