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HEATING AND COOLING OPTIONS FOR TUNNEL PASTEURIZERS

Packaged beverages can be processed to improve preservation and shelf-life; this is called pasteurization (1). We will examine the variation called Thermal Pasteurization. It occurs by heating and cooling the filled product packages according to a thermal cycle. From the thermal point of view, the tunnel is divided into 1) a pre-heating area, 2) a heat treatment area, and 3) a cooling area where the product is brought back to ambient temperature (1,2).

The cans or bottles travel through these areas progressively where water is sprayed on them to modify their temperature; those thermal changes produce a reduction of microorganisms in the beer minimizing the effect on physical stability and flavor while maximizing biological stability (microorganisms) (3). Also, any leftover yeast is deactivated. Filtered beer typically has a target P.U. range of 12 +/-2 for proper pasteurization (1 P.U. is added to the product when exposed to 60°C (140°F) for one minute) (4).

Water spray systems, including spray patterns, water volumes, and distribution systems, depend on the pasteurizer manufacturer (3). There are several options for elevating the product’s temperature to the adequate pasteurization temperature, usually using low and high-pressure steam or high-temperature water in either direct or indirect heating (5). The principles and effects of thermal preservation treatments such as this one are well established (6), and publications are widely available to delve deeper into the topic, such as the book Handbook of Brewing by Stewart & Priest (ed. 2017)(7).

The temperature at which water reaches its boiling point is a function of pressure; at atmospheric pressure, steam is created initially at 100°C (212° F). Interestingly, steam at 100°C (212° F) has a substantially higher heat capacity than the same amount of water at the same temperature.

This happens because when steam condenses on the surface of a cooler can or bottle, the latent heat of condensation is released on the surface as the steam turns from the higher energy gaseous state to the lower energy liquid state (8); producing a rapid rise in the surface temperature with little sensible heat change in the heating medium. However, high-temperature water can also be applied to beer containers by spraying or by deluging with cascading sheets or by immersion (7).

The heating of the water needed for spraying on the containers can occur by different means. Heat exchangers are often used. These exchangers contain fluids depending on the requirements, such as saturated steam, heated water, and others(9). The heat needed to pasteurize can be obtained by different options such as direct fire, gas-fired boilers, and electrically heated boilers.

In a low-pressure boiler, the pressure does not surpass 15psi while the temperature stays below 121°C (250° F). This type of boiler does not need constant monitoring. On the contrary, high-pressure boilers heat steam more than 15psi, and temperatures exceed 121°C (250° F). High-pressure boilers must have a boiler operator on staff to constantly monitor valves, switches, safety devices, or leaks.

Some manufacturers recently have adopted a centralized heating system (2). This system involves a single heat exchanger for all areas subjected to temperature control, providing heating a quantity of water maintained at a sufficient temperature for mixing with the process water of various areas depending on each area’s needed temperature. In this way, thermal energy is distributed by masses of hot water added in the different areas where a rise of temperature is required (Panella & Pasoli, 2000).

Cooling is required to lower the product temperature in the third area of a tunnel pasteurizer, a temperature that is acceptable for labelling, packing, and storing. The cooling is usually done by direct injection of a cooling medium; this medium could be potable water obtained from a municipal water system or private well. Also, the cooling water could be recycled from the process and cooled mechanically in a cooling tower or water cooler (5).

Glycol is a cooling liquid typically used in refrigeration systems; the addition of glycol changes the freezing point of water from 0°C (32° F) to -15°C (-60° F). Water/glycol mixtures have also been used in high-temperature short-time pasteurizers.

The brewing of beer requires large amounts of thermal and electrical energy; breweries nowadays use 7.5–11.5 kWhel and 16.7–33.3 kWhth per hectoliter of beer (10), while the annual output of medium to large breweries could be up to one million hectoliters. In the brewing industry, 80% of this energy is for process heating(11).

Early pasteurizer manufacturers made little attempts to conserve or reuse the energy used in heating and cooling the product during the tunnel pasteurization process. Later, initial attempts to conserve resources and energy resulted in “regeneration” of water cooling/heating (12).

This means that the spray water is cooled as it raises the cool product’s temperature before being pumped to the “regenerative pair,” the zone where the cooling spray is heated up as it cools the hot product pumped to the cold zone. This results in a heat transfer system called “regeneration” (9). Tunnel pasteurizers can potentially have several regenerative pairs.

Pinguli et al. (2018) conducted research to identify areas of opportunity for breweries’ energy efficiency. They found out that the areas of action that could produce immediate results include condensate return systems, recycling of cooling water, effective control of boiler efficiencies, developments in electrical power consumption and water and heat recovery in pasteurizers (13). This is important since having high quality manufactured tunnel pasteurizers will provide more energy efficiency. Furthermore, there are also attempts to implement solar energy for heating needed in the brewing of beer.

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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.

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References:

1. Bhuvaneswari E, Anandharamakrishnan C. Heat transfer analysis of pasteurization of bottled beer in a tunnel pasteurizer using computational fluid dynamics. Innovative Food Science & Emerging Technologies. 2014 Jun 1;23:156–63.

2. Herold JL, Nekola WJ, Wehmiller FW. Process of pasteurizing liquids in containers. US2282187A, 1942. Available from: https://patents.google.com/patent/US2282187A/en

3. Richmond DW, Clyne CW, Holben TM. Pasteurization process [Internet]. US4693902A, 1987. Available from: https://patents.google.com/patent/US4693902A/en

4. Broderick HM. The Practical brewer. A manual for the brewing industry. 1977;

5. Becker KW, Jr LGF, Kropp L, Straka RB. Pasteurization method [Internet]. US4490401A, 1984. Available from: https://patents.google.com/patent/US4490401A/en

6. Stumbo CR. Thermobacteriology in food processing. Elsevier; 2013.

7. Stewart GG, Russell I, Anstruther A. Handbook of Brewing. CRC Press; 2017. 799 p.

8. Purnell G, James C. 8 – Advances in food surface pasteurisation by thermal methods. In: Demirci A, Ngadi MO, editors. Microbial Decontamination in the Food Industry [Internet]. Woodhead Publishing; 2012 [cited 2020 Dec 30]. p. 241–73. (Woodhead Publishing Series in Food Science, Technology and Nutrition).

9. Panella G, Pasoli G. System for controlling the pasteurization heat treatment, in particular of packaged food products, in tunnel-type pasteurizers [Internet]. US6142065A, 2000 [cited 2020 Dec 29].

10. Mauthner F, Hubmann M, Brunner C, Fink C. Manufacture of Malt and Beer with Low Temperature Solar Process Heat. Energy Procedia. 2014 Jan 1;48:1188–93.

11. Lauterbach C, Schmitt B, Vajen K, Jordan U. Solar Process Heat in Breweries-Potential and Barriers of a New Application Area. Renew Energy. 2009;645–7.

12. Adam F. Apparatus for pasteurizing and cooling food products [Internet]. US9943093B2, 2018 Available from: https://patents.google.com/patent/US9943093B2/en

13. Pinguli L, Malollari I, Lici L, Llupa J. Efficient Use of Energy An Important Approach In Minimizing Environment and Operational Costs in Albanian Breweries.

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