The brew kettle is possibly the most critical piece of equipment in the brewhouse. The wort boiling process is where intense heating will condense the wort, drive off unwanted volatiles like DMS, develop malt flavors, isomerize and solubilize hop acids, and effectively sterilize the wort prior to subsequent cooling and yeast pitch. In order for the brew kettle to perform its job successfully its heating surfaces must be clean enough to efficiently transfer heat to the wort.
|Figure 1. Brew
kettle build up (Photo by K. Ockert)|
Brewhouse soils present a different cleaning challenge than those in the cellars. The brewhouse is a cooking operation and precipitated soils are heat-hardened onto the surfaces of the heating elements, jackets, and vessel itself. Although this is an issue with all brewhouse vessels, the brew kettle has the most intensive heat application and hence the most resistant surfaces to clean. Boiled wort leaves behind a matrix of carbohydrates, proteins, and minerals, which cook onto the kettle walls as well as steam-heated jacketing, coils, and the calandria. This appears as a brown build up (Fig 1) and is not easily removed with the protocols found downstream in the brewery. To complicate the cleaning effort, there is shadowing from various heating elements, bracing, baffling, access ladders, and even from the CIP spray nozzles themselves.
In addressing kettle cleaning it is first important to take the issue of shadowing into account and install CIP spray balls or impingement cleaning machines that will cover all areas (including themselves). Position the CIP nozzles so that they overlap sprays and can clean from both above and below the areas that need detergent application. Not only will the CIP nozzles need to be positioned correctly but the entire CIP process will rely on adequate flow to supply the capacities required for the nozzles. CIP systems will commonly employ a high speed (3600 rpm) centrifugal pump of hygienic stainless steel construction, utilizing a water flush mechanical seal to reduce attack from the harsh chemicals used. The pump capacity should be calculated by adding up the nozzle requirements at the pressure specified and adding additional volume on top of that for a safety margin. For instance, if there are four spray balls in the kettle and each requires 25 gpm at 50 psig, then the pump should deliver at least 100 gpm plus a margin at 50 psig. It is best to consult your supplier for CIP nozzles and pumps to determine the best spray equipment strategies and supply pump requirements.
The cleaning strategy for brew kettle cleaning is normally built on a caustic (sodium hydroxide) solution base to remove organic carbohydrates and proteins along with a protein oxidizer to peptonize and break up the protein matrix making it easier to remove. Some formulations will use a chelating agent like EDTA to help remove minerals. The least expensive oxidizing additive is sodium hypochlorite (bleach) at 100–200 ppm active content. In an alkaline caustic environment the chlorine is not corrosive to stainless steel and does a good job of breaking down the protein so that the caustic solution can remove the residual organic soils. However, as it reacts to the organic load it will deactivate, and so some protocols or systems will include either continuous injection or a chlorine addition in the middle of the cycle to refresh the active chlorine content.
Hydrogen peroxide at 1000 to 2000 ppm is a chlorine-free substitute for bleach and will accomplish the same goal in breaking down kettle protein buildup. While more expensive, the hydrogen peroxide is less likely to corrode stainless steel, is somewhat safer to use, and is biodegradable. Both additives work well to remove the troublesome protein–carbohydrate soil.
Caution should be used in handling hydrogen peroxides or chlorine bleach, as they are strong oxidizers and will attack skin and eyes! Employees must be be trained and use caution when handling these chemicals and absolutely wear personal protective equipment (i.e., rubber gloves, eye protection, etc.). Chlorine bleach will produce potentially deadly chlorine gas in an acid environment that will damage the lungs. It is very important to take safeguards assuring that employees cannot mix chlorine bleach with acid.
Brew kettle solutions are normally the strongest used in the brewery outside of bottle washers in the packaging hall. The CIP solutions will commonly be up to 3% active caustic along with the oxidizer additive and circulated at 140–185 °F (60–85 °C). Quite often an acid cleaning cycle of a 1–2% nitric-phosphoric blend will be applied after the complete rinsing of the caustic solution. The acid will remove remaining mineral build-ups that might still be left behind and shine up the surface. Note that if chlorine bleach has been used in the caustic circulation, it must be completely rinsed away prior to the acid CIP as it will be highly corrosive and hazardous to employees, as noted earlier.
The efficacy of the cleaning protocol should be reviewed periodically and optimized for chemical concentrations, temperature, and circulation times. Additionally, the interior of the kettle should be inspected to make sure that CIP spray equipment is reaching all surfaces and is not clogged.
Each brewhouse situation will differ as to how often to CIP and clean the brew kettle. As the fouling increases from brew to brew, the heat transfer efficiencies decrease, the effectiveness of the boil diminishes, and energy is wasted. The brewer must decide how many brews to allow between kettle CIP’s through their own trials. In many smaller operations it will simply be at the end of the day or week, but to operations running around the clock through each week these cleaning periods mean lost production. The number of brews between CIP is determined carefully and reviewed periodically. As a result, many newer kettle calandria designs have been made as “self-cleaning,” meaning that the flow of the wort past the heating surface actually keeps it clean, a priority. The self-cleaning units are meant to keep the heat exchange surface soil-free, maintaining their specified heat exchange capabilities with accompanying decreased downtime and increased production.
Brew kettle cleaning is robust and involves strong, hot chemical solutions to break down a very pernicious protein/carbohydrate/mineral complex. However, with proper application, spray balls, or cleaning machines, as well as a properly sized CIP pump, the kettle will come clean along with the rest of the brewhouse vessels and piping.
Consult your cleaning chemical supplier for the types of chemicals to use, their concentrations, application protocols, and safety preparations. Using that information as well as running trials to optimize the function standard operating procedures can maintain the brew kettle so that proper boiling occurs for each brew.