Omitting the process of brewing craft beer, beer equipment is used to add wort and boil it. After boiling, the thermosetting substances are separated from the wort as soon as possible using physical methods to obtain clear wort. The next step is to cool the wort to the required fermentation temperature according to the process. During the cooling process, wort aeration should be performed to provide enough oxygen for yeast reproduction. The methods of separation include the cooling plate method, sedimentation tank method, and Whirlpool method.
Processing of Wort after Boiling
The purpose of processing the wort after boiling is to separate the hot and cold coagulations in the wort as quickly as possible to obtain a clear liquid. The wort is then cooled to the fermentation temperature required by the process (6-9℃ for lower fermentation and 12-18℃ for upper fermentation). During the cooling process, wort aeration is necessary to provide sufficient oxygen for yeast multiplication.
Main Tasks of Wort Post-processing
The main tasks of wort post-processing include hop lees and thermal coagulation separation, wort cooling, wort aeration (supplying oxygen to yeast), yeast addition, cold coagulation separation, yeast reproduction, and secondary aeration.
Thermal coagulation is an insoluble condensate formed by the condensation of high molecular nitrogen during the boiling process of wort. It precipitates out with protein denaturation, continuous oxidation and polymerization of polyphenols, and also adsorbs part of hop resin and other organic substances.
Factors affecting the amount of thermal coagulation include:
- The amount of precipitation of thermal coagulation is related to the amount of nitrogenous substances in the wort and the solubility of the malt.
- When suspended in the fermentation broth, the thermal coagulation adsorbed by yeast cells can affect normal fermentation and sedimentation. Additionally, thermal coagulation in the wort can lead to increased beer color, rough taste, long aftertaste, poor foam stability, and taste stability.
The Whirlpool tank is a flat-bottomed closed cylindrical vessel with a 2% slope at the outlet. The ratio of the height of the wort level to the diameter of the tank is 1:2-3, with modern Whirlpool tanks using a ratio of 1:3. The tank is equipped with an insulating layer to prevent wort cooling. The center of the tank bottom has a conical hot solids collection cup for better collection of hot solids. The wort enters the tank tangentially through two inlets: one at the bottom to avoid oxygen absorption, and the other at 1/3 of the height from the bottom.
- The wort enters the trough tangentially to form a rotary motion. After feeding, the rotating wort decelerates, resulting in a swirling effect.
- The solids in the wort move towards the center of the trough due to the combined force of gravity and centripetal force, following the natural deceleration and rotation caused by the swirling effect.
The rotation of the wort should take advantage of the “Coriolis” inertial force generated by the Earth’s rotation from west to east. In the northern hemisphere, the correct direction of rotation is counterclockwise to avoid energy wastage. In the southern hemisphere, it should be clockwise.
Important Technological Factors in Post-processing of Wort
The heating time should be short, with a total time of less than 60 minutes.
The delivery of hot wort should be smooth and gentle to prevent air entry and formation of air bubbles. It should not destroy the hot coagulation when pumping and flowing through piping.
Considering the nature of hot coagulation, the cyclone sedimentation tank should have multiple openings, and the wort pump should operate without cavitation.
Cooling and Oxygenation of Wort
After boiling and pouring the wort into the rotary sedimentation tank, the following treatments should be carried out:
- Rapid cooling to bring the wort temperature to the level required for yeast inoculation.
- During wort cooling and aeration, yeast can synthesize necessary substances like sterols and unsaturated fatty acids only when absorbing enough oxygen.
- Precipitation and separation of hot and cold coagulants in the wort to ensure normal fermentation and desired beer quality.
The cooling equipment used for wort cooling should meet the following requirements:
- The parts through which wort and cooling water flow should be easy to clean.
- The equipment should be well-sealed to prevent leakage of cooling water and wort.
- A sufficient cooling area is needed, with a short cooling time and a large amount of cold solids precipitation. The heat recovery rate of the plate heat exchanger should be > 95%, and there should be a small temperature difference between the front and rear cooling areas. The hot water temperature should be raised as much as possible.
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