The heart (and heat) of dairy processing

Meet the panel

Dan Björklund, Manager, Dairy Chilled & Fermented Solutions, Tetra Pak, Lund, Sweden

John C. Bohn, Founder and Director of Sales and Marketing, AGC Heat Transfer, Portland, Ore.

Rick Earley, Beverage and Dairy Market Manager, Admix, Greensboro, N.C.

Carl Lemke, Business Development Manager, Heat Exchangers, Alfa Laval, Kenosha, Wis.

David M. Miles, Vice President, MicroThermics, Raleigh, N.C.

   Bill Snow, Technology Group Manager, SPX Flow Technology Systems, Delavan, Wis.

Heat exchangers are key components in a dairy processing plant that can directly affect food product quality, a supplier tells Dairy Foods. Other suppliers tell us that pasteurizers are not all alike. To learn more about processing milk and the equipment that is used, we convened a “virtual roundtable” of equipment manufacturers. What follows are edited remarks received via e-mail.

Dairy Foods:True or false: A pasteurizer is a pasteurizer is a pasteurizer. What key points are important for a dairy processor to know about pasteurization equipment?

David M. Miles: This is definitely not true. While reaching a qualified hold time and temperature will ensure that the product is truly pasteurized or sterilized, the heating rates and cooling rates have a huge affect on product quality. This is especially true in UHT- and aseptic-processed products.

Essentially, the heating (and to a smaller extent, cooling) rates actually have a larger impact on the quality of the product. So, it might be properly pasteurized or sterilized, but the process will affect the palatability of the product.

We see this often when working with clients because they have variability in product quality from one processing location to another. In the end, we simulate both to enable them to make a formulation that is robust enough to provide the product identity they need. This can include not just organoleptic qualities, but nutritional qualities as well.

We have even worked with clients who end up changing one or more production lines so that they all have the same or similar heating profiles so that they can have control over their product quality.

John C. Bohn:False. In the sanitary plate heat exchanger field there are obvious differences in surface finish, plate gap, plate thickness and after-sales support. Cleaner-looking bright anneal (BA) surface finishes (not a dull 2b finish) allows processors to easily determine if they’re getting a good CIP (clean-in-place) response.

Plate gap (the distance between the plates) and a viscous and CIP-friendly inlet design is important for extending the run times and/or reducing operating pressures with viscous products.

Dan Björklund: In the past, dairy pasteurizers have often been regarded more or less as commodities, simply a plate heat exchanger with a pump and a holding cell. But is it really that simple?

Growing price pressure on milk and increasing energy costs are forcing processors to focus on the total cost of ownership. When all these costs are taken into account, the differences between pasteurizers can be significant.

The focus on food safety is also growing. Where pasteurizers are concerned, differentiating factors will obviously concern both the cleanability of pasteurizer design and the uniformity of performance, that is, to consistently deliver a process that fulfills pasteurization criteria.

But there is also another key factor. The role of pasteurization in the value chain is just one step, so producers are increasingly recognizing the value of focusing on an entire solution, from raw milk intake to the packaged product, with uncompromising food safety and full traceability throughout. When this can be achieved with a low total cost of ownership, there is suddenly no such thing as “just a pasteurizer.”

Carl Lemke: False. Key points [about pasteurizers] have not changed much over the years. They are:

• Thermal and mechanical impact of the design on product quality
• The cleanability of the system
• Reliability of the equipment
• Energy savings in form of heat recovery achieved
• Overall operating efficiency and reliability

Particular attention should be paid to the last points, given the cost of energy and costs associated with downtime and repairs.

Dairy Foods: Some dairy processors also manufacture nondairy juices, drinks and teas. What do they need to know about processing these beverages?

Miles: When making high-acid aseptic juices, the traditional paradigm was that you had to address yeasts, molds and lactics. This no longer holds true due to the increased prevalence of Alicyblobacillus. The increased prevalence of this organism is ostensibly due to the increase in high-acid, shelf-stable products.

The characteristics that make this a troublesome issue are that this bacteria grows in high-acid products and produces spores that are completely unaffected by traditional temperatures used in high-acid aseptic processing and hot-filling. While not pathogenic, it causes spoilage of high-acid products over a period of time that allows the product to get to the store shelves before it is found.

It does not cause much if any change in appearance of the product, nor does it cause the product packages to swell. It does cause is a bad off-flavor often described as “like medicine.” Thus, it can cause considerable consumer complaints because it actually does not have any outward indications of spoilage, but the consumer literally gets a “bad taste in their mouth” from the product. No producer wants this.

Increasing hold times to address this organism is not feasible (hold times may need to be increased to hundreds of seconds). In order to address it with heat only, the process temperatures need to be increased to over 230F. For some producers, this may not be difficult. For others, a change in their processing equipment will be needed. And for others, it is simply not an option at this time.

As such, many producers are looking to “control” the occurrence of the bacteria with in-house cleaning procedures and by pushing better cleaning requirements up the line to their suppliers. However, over time, this may not be sufficient. In the end, since this is a truly ubiquitous organism, and more and more high-acid, shelf-stable products are being produced; the only way to truly be rid of the problem is through proper processing.

Bohn: Nondairy juices, flavored drinks and tea from concentrate have been run for years on standard HT/ST plate pasteurizers by either blending products in a tank, direct injection or in the raw balance tank.

Fresh-brewed tea can be run using a continuous batch process incorporating a unique regeneration section to pre-cool the freshly brewed tea while pre-heating the next batch of water. Proper sizing and control of this special heat recovery section can enable the processor to obtain reduced operating costs and also make them eligible for a one-time commercial energy company rebate program [approximately $45,000, based on a recent installation].

Rick Earley, Beverage and Dairy Market Manager, Admix, Greensboro, N.C.: If they effectively de-agglomerate their higher solids product with an inline disperser or mill as a final step before processing, they may still be able to utilize plate heat exchanger technology (as opposed to tubular/scraped surface) without cleaning/allergen issues.

Bill Snow, Technology Group Manager, SPX Flow Technology Systems:These products are not regulated by the same PMO regulations as dairy products.  The times and temperatures for adequate pasteurization vary with product and with the pH.  Some are considered high-acid and some can be low-acid.  To be safe, the pasteurization process should follow Hazard Analysis Critical Control Point (HAACP) procedures for full process validation.

Juice products may contain pulp.  At times, depending on the quantity and type of pulp, fibers may be caught in a plate heat exchanger at points of contact or in areas of low velocity.  At times, this may require the heat exchanger to be opened and inspected and sometimes manually cleaned of any fibers before a CIP can be effective.  For plants with sufficient volumes of pulpy juice operation, tubular heat exchangers are preferred, as there are fewer “pinch points” where pulp could get caught. 

Tea products also can contain tannins which may create a film on the heat exchanger plates and require different CIP procedures for removal than for dairy products.

A risk of the use of one pasteurizer system for running multiple products is of cross contamination — for instance getting orange juice pulp in milk products.

Dairy Foods: Discuss the role heat exchangers play in dairy processing. What are some of the best practices that processors should be following?

Lemke:Heat exchangers are usually at the center of the process. Careful attention to the required specification and comparison of competitive design offerings is essential. In many cases there is considerable flexibility in how the application engineer can approach a particular heat exchanger design. Interpretation and assumptions are often asked of the application engineer, however, it’s important for end users and system builders to understand that small variances in temperature profile, heat recovery, system pressure drop and product properties can substantially affect the cost, design and function of the heat exchanger.

Miles: Aside from cleaning, CIP, SIP [sterilize (or sanitize) in place] and preventative maintenance, I would say that matching the product with the process (that is, heating curves from the heat exchangers) is one of the most important practices that processors should be following. This means that production equipment should not be used for R&D. It isn’t designed for it and is very costly.

Bohn: There still are some processors who are not taking advantage of our field leak test. They should take advantage of this valuable service to maintain and monitor one of the key pieces of equipment in their plant.

[Bohn is chairman of the 3-A Sanitary Standards Committee WG-5, which covers all types of heat exchange.] 3-A recently passed a revised standard (3-A 11-09) covering plate type heat exchangers. That new standard reads:  “it is recommended that leak detection and visual inspection of all plate heat exchangers be performed at least once every 12 months and a record of inspection results maintained.”

It goes on to state that the methods of inspection “should be capable of detecting any leakage within the heat exchanger irrespective of the size,” which eliminates previously allowed helium, salt and bubble test methods.

Björklund:Because they are compact and efficient, plate heat exchangers  are normally the first choice in dairy processes, as long as there are no particles in the product or the processing temperature is not too high (< approximately 250F). For higher temperatures or when the product contains particles/fibers, a tubular heat exchanger is the best option.

Heat exchangers are key components that can directly affect food product quality, so it is important that both plates and frame are designed specifically for food processing. Achieving efficient cleaning and gentle product treatment in the heat exchanger requires efficient distribution of the product and cleaning fluid over the plate and having a length/width relation and connection sizes that match the product/cleaning flow rate.

In order to maximize the lifetime of the plate pack, it is important to avoid pressure shocks and to minimize the pressure fluctuations in the system. Producers should avoid cleaning/disinfection agents that may cause corrosion and check the chloride levels in the water. An automatic opening device is helpful in monitoring the cleaning and the condition of the plates.

Find the best pasteurizing process for your foods and beverages

Dairy Foods asked: What foods are best pasteurized by vat pasteurization? By high-temperature/short time (HT/ST)? By higher-heat/shorter time (HH/ST)? By ultra-high temperature (UHT)? Here’s what Bill Snow of SPX Flow Technology Systems had to say:

Vat pasteurization is typically used for low-volume production today. This may include goat milk or on-farm pasteurization where the volume does not justify the investment in capital equipment required for continuous pasteurization. The low temperature and time of vat pasteurization also produces a product with different flavor and organoleptic properties preferred by some customers. Products that require more residence time for flavor and/or body development (such as high-quality ice cream mixes) may still be processed in vat pasteurizers.

Standard fluid milk products and most ice cream mixes are typically processed in the HT/ST process. The process is designed to kill all pathogenic micro-organisms, but not to “sterilize” the product. The product must be held in refrigerated conditions after packaging, and the actual shelf life will depend on the quality of the milk before pasteurization and the conditions of handling after pasteurization. Products processed by HTST are generally intended for relatively local distribution and used by the consumer in seven to 10 days.

HH/STis a process used for extending shelf life of normal dairy products by heating to higher temperatures and shorter times. As a result, the remaining viable micro-organisms are reduced, resulting in longer shelf life under refrigerated conditions. The products may be packaged using standard liquid dairy fillers and packages, or ultra-clean fillers and packages to minimize post-pasteurization contamination. Coffee creams, whipping creams and other products that require long shelf life are typical products that may be processed on HHST as well.

UHTis a term used generally for aseptic products. Low-acid aseptic processing and packaging systems are regulated by FDA CFR 21 Part 113 rather than the Pasteurized Milk Ordinance. Any fluid milk or other dairy products can be UHT processed. The advantage of UHT is that the product processed and packaged in this manner does not need to be held in refrigerated conditions, and is “commercially sterile” under FDA regulations. The shelf life is often six months to 12 months or longer. 

Suppliers upgrade the equipment in pasteurizing systems

It sounds like an Olympics motto, but today’s equipment is faster, runs longer and achieves higher temperatures. Makers of pasteurizers and heat exchangers talk about equipment upgrades.

Designers of processing equipment recognize some of the economic realities of today. Energy is expensive, so equipment is more efficient. Real estate is expensive, so equipment takes up less space. Labor is expensive, so equipment runs more efficiently and reliably.

In the previous article (“The heart and heat of dairy processing”), equipment vendors talked about the process of pasteurizing milk. In this report, they talk about the technological upgrades and new features they incorporated to their systems.

The Alfa Laval Frontline 15 Automatic offers processors the largest sanitary heat exchanger available in the world, said Carl Lemke of Alfa Laval.

“With 6-inch porting and up to 9,000 square feet of surface, it is almost twice the size of competitive offerings,” Lemke said.

This provides processors operating efficiencies through reduced floor space requirements and the ability to achieve high rates of heat recovery at high flows, with minimum product shear and system pressure drop.

David M. Miles of MicroThermics Inc. said that in the food research industry, his company specializes in thermal process simulation. MicroThermics won the 2011 Industrial Achievement Award for its Direct Indirect UHT/HTST processor because of its ability to truly provide production processing conditions.

“We utilize a number of methods to analyze production processes, and then build equipment to match the time/temperature histories,” Miles said.

The company builds flexibility into its equipment so that it can simulate a wide range of time/temperature histories. Thus, clients can closely simulate the variety of processes found industrially, even within the same “process conditions,” Miles said.

Updates and new features make the equipment easier to use, and MicroThermics provides customers real-time online process support.

“This enables us to log into our clients’ processor and help them troubleshoot or analyze a process in real time.  We can literally operate most of their processor from our offices if necessary,” Miles said.

John C. Bohn said AGC Heat Transfer has a new “fixed footprint” automatic
hydraulic open-close frame. Model AR51-D allows processors to install a new HTST unit and select a frame size large enough for any future increased flow, he said.  Future increases in flow can be easily achieved by addition of plates only and the existing frame will be capable of handling the larger number of plates within the same fixed footprint, Bohn added. 

“We’ve also included a simple hydraulic closure system with only two spindles and no PLC (programmable logic controller) so operation is simple and accurate.”

Inline dispersing/milling technology is allowing dairy processors to reduce the pressure on (or completely eliminate) conventional homogenizers, said Rick Earley of Admix Inc. This results in significant savings in water and energy consumption, initial capital investment and ongoing maintenance expense.

Bill Snow said the hydraulic frame closures on the manual and powered versions for SPX Flow Technology Systems’sBinary and Quad Drive plate heat exchanger allow for easy and safe opening and closing. The EasyFlow plate series is said to be highly responsive to clean-in-place procedures. Features include ease of gasket replacement and self-locking alignment features.

One technology improvement from Tetra Pak is a new inlet valve arrangement of the balance tank that reduces the mixing phase of the product by as much as 50%, said Dan Björklund. The inlet solution features an electronic level control and a frequency-controlled product pump that lowers energy consumption even further.

Another area of major improvement is CIP. The latest generation of Tetra Alcip has been fitted with an array of intelligent new functions that reduce water consumption and increase the accuracy of detergent concentration.

The company’s newest Tetra PlantMaster enables an entire line (including filling and logistics systems for packaged and palletized products) to be run by a single automation control system.

“Apart from what this means for plant-wide efficiency and cost reduction, it also enables full traceability. Could this make it possible for a consumer to scan a bar code on a milk package and find out what farm the milk came from? It’s already been done,” Björklund said.n