Batch and Tunnel Pasteurization for Cider/Hard Cider Production
Cider, also known as “hard cider” in North America, is the product of apple juice’s alcoholic fermentation. This fermented beverage has an alcohol content between 3.0–8.5% with a soft acidic, and sour taste (1). In traditional farmhouse cider-making, the fermentation processes are performed by indigenous yeast, while in the commercial path, unfiltered fruit juice is inoculated with the yeast of different species; the most common are Saccharomyces, Kloeckera, or Pichia (1) which induce anaerobic fermentation converting sugar to ethanol (2).
Cider making is similar to winemaking; however, cider usually contains lower ethanol than wine (5-7% vs. 11-15%), and for this reason is more prone to microbial spoilage (3). Refermentation in the package and consequent bottle explosion has been a concern for cider makers since years ago; besides, refermentation from certain types of bacteria such as Zygosaccharomyces is a cause of harm for consumers (4). To avoid this, hard cider pasteurization is used to preserve product safety and quality.
Through cider pasteurization, microbiological organisms are inactivated to reach stability and increase cider shelf life. The process involves heating the product to approximately 60 °C (140 °F) for a determined period of time. If the cider is under-pasteurized, the microorganisms might survive, while over-pasteurization could result in flavor and other attribute changes (5). Pasteurization has evolved in the last decades from simple (but labor-intensive) to automated methods; newer methods utilize batch or tunnel pasteurizers.
There are several options for cider pasteurization, including non-thermal and thermal (1). The non-thermal processes include high-pressure (6), ultrasound (7), UV-irradiation (6), and pulsed electric fields (8). Although some of these methods have been approved already by the Food and Drug Administration, most of them are still limited in commercial applications because of their effectiveness (1).
Therefore, thermal processes are considered to have the most microbial safety, and are the most cost-effective (9). The Cider Institute of North America might be a good resource for delving deep into hard cider pasteurizers; otherwise, the fundamental book: Review of Potential Pasteurization Methods for Apple Cider.
Cider pasteurization can be performed using a batch pasteurizer or a tunnel pasteurizer, measured in pasteurization units or PUs defined as 1 PU when the product is exposed to 60°C (140°F) for one minute (10). However, in the cider industry there is no established standard regarding the sufficient number of PUs needed. While the beer industry has defined a range of 12 +/-2 for proper pasteurization, some cider makers have reported using between 10-25 PUs for hard cider, while a magnitude of 20-25 PUs or even higher is used by others (11).
Using an insufficient amount of PUs can result in limited microorganism destruction and spoilage; on the other hand, using excessive PUs could lead to economic losses and energy expenditures (3). Additionally, cider is considered a “healthy” drink because phytochemical and antioxidant profiles are elevated in cider compared to the juice (12).
If incorrect cider pasteurization happens, it may result in physiochemical changes altering sensory modifications or reducing the bioavailability of important antioxidants in the product (3). We should have in mind the crucial goal of reducing the risk from microorganisms, but also, it needs to be balanced with retention of quality attributes.
The terms batch pasteurizer, vat pasteurizer, and low heat pasteurizer generally mean a process of heating every particle of the hard cider. As the Review of Potential Pasteurization Methods for Apple Cider recalls, the batch process stores a quantity of cider (for example, 100+ gallons) in a vat that is heated and agitated at the same time, to a temperature of approximately 63 °C (145°F) and held for 30 minutes. The specific temperature and holding time eradicates the microorganisms and makes the product safer for consumption.
Although, this capacity might be considered reduced for commercial needs. A multipurpose vat is used for batch pasteurization, which is an insulated, cylindrical vessel with a double jacket. The tank is heated by circulating hot water or steam in the inner jacket. The cider is slowly heated, and after reaching the required temperature, is held for the required amount of time (typically 30 min); during the heating process, the product is agitated slowly.
Finally, it is cooled to below 4 °C (39 °F), which may be accomplished through air cooling or by dipping in a cool water bath. Another type of batch pasteurizer is a Spray Batch Pasteurizer. In a spray batch pasteurizer, the cider is heated in the bottle or can by multiple spray headers (nozzles) coating the bottles or cans with heated water. This method of heating is preferable to a tank or vat batch pasteurizer because the heating process is more uniform.
A tunnel pasteurizer works with the heating transmission principle; it includes a shell, tube heat exchangers, and steam water heating. The pasteurizer takes the cider bottles or cans through heating and cooling zones for a specific time. In this kind of process, the packages are moved on a conveyor within the tunnel while water is sprayed on the packages (13). The tunnel is divided into 3 to 15 spray zones: preheat, heating, holding, and cooling (14).
The temperature of the water sprays is predetermined and controlled depending on the PUs requirements of the product. There are different references of design, features, and capabilities of tunnel pasteurizers for cider; for example, spray patterns, water volumes, and distribution systems depend on the pasteurizer manufacturer. Also, certain systems have the water running off the packages collected in reservoirs, heated, or cooled, and recycled to the sprays again (5).
Other characteristics of the product are important when considering pasteurizing cider, such as bottle size, material, and shape, which may influence the process (15). Also, depending on the fruit from which the cider is made, for example, apple, pear, cherries, etc., the hard cider will have a different ethanol content (2), which research has shown to be an important contributor to the heat process. Other important factors related to the cider’s particular chemistry relevant to the pasteurization process are pH and sulfur dioxide concentrations (3).
The Cider Academy (UK based) might be a resourceful website for discussing the different types of pasteurization processes, production equipment, packaging, and laboratory analysis.
Another cider resource is the American Cider Association at https://ciderassociation.org/
Ed Michalski Bio
Ed Michalski started his career in the beverage industry by designing stainless steel, higher flow spray headers for Pabst Brewing. Along with the headers he also designed a matching process to produce those headers.
Ed, along with his brother David, formed PRO Engineering/Manufacturing, Inc. and became the primary vendor to Miller Brewing for pasteurizer re-design and refurbishment.
He developed a conversion process that changed the conversion of walking beam pasteurizers to flat mat. With his modular design the conversion was reduced from 7 weeks to 2 weeks.
His goal has always been reduction of labor costs and time. Reduced downtime for projects and maintenance are a key goal as extra hours for conversion and general maintenance are hours that are lost forever.
Based on what they learned by re-designing and refurbishing other manufacturers’ pasteurizers, Ed and PRO started to offer the pasteurizer marketplace awesome pasteurizers.
PRO and Ed have been designing and manufacturing great pasteurizers for over four decades.
PRO Engineering and Manufacturing was established in 1977 by Ed and Dave Michalski as a steel fabrication shop. For more than 40 years, PRO Engineering and Manufacturing, Inc. has been delivering solutions for beverage product shelf stability and consumption safety. As leading innovators in post-fill pasteurization, our skilled team offers the best in high-quality pasteurization equipment.
Phone: 414-362-1500 | Email: [email protected]
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