The dirt on the walls of the fermenter is a mixture of inorganic and organic matter, making it difficult to clean using a single cleaning agent. Using only caustic soda for fermenter cleaning will only remove organics. To achieve better cleaning results, the cleaning temperature needs to exceed 80°C. When cleaning, using only nitric acid will have a certain effect on inorganic substances but almost no effect on organic substances. Therefore, fermenter cleaning requires both an alkaline cleaning solution and an acidic cleaning solution.
Cleaning Steps for Fermentation Tanks
- Drain the residual carbon dioxide gas in the tank by using compressed air to displace the carbon dioxide for 10-15 minutes (depending on the airflow).
- Rinse the remaining yeast in the fermenter with clean water and then rinse the fermenter with hot water at 90°C to warm it up. Disassemble the discharge combination valve and the aseptic sampling valve, use a special brush dipped in lye to clean them, and reinstall them.
- Circulate the fermenter with 1.5-2% hot alkaline water above 80°C for 30 to 60 minutes. Rinse the fermentation tank with hot or warm water until the discharge liquid becomes neutral, and then rinse the fermentation tank with cold water until it reaches room temperature.
- Use a 1-2% nitric acid solution or an acidic cleaning solution for 15 minutes.
- Rinse the fermenter with water to neutralize the drain.
Sterilization of Fermentation Tanks
To sterilize the fermentation tanks, circulate and clean them for 30 minutes using a diluted peracetic acid solution at a ratio of 1:200-250 or hydrogen peroxide of suitable concentration. Recover the peracetic acid solution and seal the fermentation tanks for use. Throughout the entire cleaning process, maintain a positive pressure of 0.01-0.04 MPa in the fermentation tank. By conducting strict cleaning and disinfection work, the stability of the brewed beer can be further improved.
Why Clean and Then Sanitize
Cleaning the dirt first ensures that only bacteria remain, allowing the bactericide to come into full contact with the bacterial surfaces and effectively kill them. If there is still dirt present, the bactericide may not be able to reach some bacterial surfaces, which could lead to rancidity in the next batch of beer. In actual production operations, it is always necessary to clean first and then sanitize.
Common Problems Encountered in Fermentation Tank Cleaning
The fermentation process produces a significant amount of organic substances such as protein, hop resin, polysaccharides, and yeast, as well as inorganic substances like calcium oxalate and sulfates. After emptying the fermenter, yellowish-brown organic and inorganic dirt adheres to the tank walls. When there is a large amount of tartar, the surface may appear white, resembling the epidermis of saline-alkali ground. The use of caustic soda only removes organic matter, and increasing the temperature by approximately 10°C accelerates the chemical reaction speed by about 1.5 times. Therefore, hot alkali is generally used to clean small fermentation tanks. When cleaning, using only nitric acid or an acid cleaning agent has a certain effect on inorganic substances but is almost ineffective against organic substances. Due to the mixture of inorganic and organic substances on the walls of the fermentation tanks, a combination of alkaline and acidic cleaning solutions is required for effective cleaning.
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