WHITE PAPER

New processing methods for recombined white milk

Published December 2015

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CONTENTS Introduction 3 Who is this booklet for? 3 What is recombined milk? 3 Three means to the same end 3 The challenges 4 Quality of milk inputs 5 Milk powder quality 5 Milk fat 6 Water 7 Stabilizers and emulsifiers 7 Best-practice production processes for recombined milk 8 Processing factors 8 Other processing considerations affecting long-term storage 12 Production process 1 – batch production 13 Benefits of batch processing 14 Production process 2 – continuous single-stream blending 15 Benefits of single-stream blending 16 Production process 3 – continuous multi-stream blending 17 Benefits of multi-stream blending 18 Total cost of ownership (TCO) 19 Environmental performance indicators 21 Choosing equipment 22 Tetra Pak – your dairy advisor 23

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Introduction

Who is this booklet for? This booklet is for anyone working in the dairy industry who is concerned with improving the quality of recombined white milk, as well as reducing the total cost of operation of dairy processing.

What is recombined milk? Recombined milk is the liquid milk obtained by adding skim milk powder (SMP) to water and adding milk fat separately to achieve the desired fat and total solids content.

This is important in regions where there is no domestic milk production, where milk production may be seasonally irregular, or where the raw milk would have to be transported over long distances. Milk powder is easier and cheaper to transport long distances, since the weight of the water has been removed.

Stabilizers and emulsifiers are often added to facilitate emulsification of the fat and to improve storage stability.

Recombined milk can be used for the same purposes as raw milk: drinking, yoghurt production, cheese production, etc.

Reconstituted milk is the liquid milk obtained by adding skim milk powder (SMP) and/or whole milk powder (WMP) to water without any extra fat addition. Due to its fat content, however, WMP is much more sensitive to oxidation and requires more demanding packaging and storage than SMP. The combination of non-fat milk solids (SMP) and anhydrous milk fat/butter oil in general keeps much better than whole milk powder.

We will not treat reconstituted milk further in this booklet.

Three means to the same end There are three distinctive ways to recombine milk:

• Batch processing • Continuous single-stream blending • Continuous multi-stream blending

Batch processing is the traditional method, used by perhaps 95% of dairies that recombine milk. But while this method consistently offers the advantages of low investment costs – as long as it is used for smaller production volumes – it often yields a higher total cost of ownership for higher volumes and has limited flexibility.

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Conversely, the relatively new in-line blending methods require more advanced equipment, but permit greater flexibility, reduce the number of process steps and boast a lower total cost of ownership through, for example, higher processing capacities, reduced heating costs, and reduced storage tank numbers and sizes. All three of these factors translate into lower operating costs. Plus, they produce higher quality products, and the multi-stream blending method allows for on-the-fly recipe changes and the possibility of adding additional ingredients, such as fresh milk, palm oil, or chocolate.

The challenges The relatively new stream in-line blending methods require, not surprisingly, a high level competence to carry out. As boundaries are pushed with new equipment and processes, substantial knowledge and experience is a must to ensuring that these boundaries are not crossed. The challenges posed by recombining milk this way, which is very different from the traditional method, thus go far beyond the three general challenges involved in recombining white milk:

• The first is assuring that the inputs to the dairy process are of sufficient quality. • The second is choosing the right process and equipment to match the milk

quality and the demands of your market, as well as how you structure your processing.

• The third is to do it in the most competitive way, with the lowest possible total cost of ownership.

In this white paper we describe the three distinct production concepts for recombining milk, depending on your processing needs. Understanding your own needs, and how new technology and knowledge can support them, can lead to big savings in total cost of ownership for you.

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Quality of milk inputs The quality of the raw materials is very important for the final quality of recombined milk products. The recipes are all based on the same three inputs:

• Milk powder • Milk fat • Water

In addition, many processes also call for adding stabilizers and emulsifiers to ensure stable products.

Thus the key measurable variables in product inputs are:

• Powder quality • Moisture content of powder • Fat content and fat quality • Whether other types of oils besides milk fat are used • Water purity

Milk powder quality Skim milk powder is classified into categories depending on the intensity of heat treatment the milk has been exposed to prior evaporation and drying. The whey proteins are denatured by heat and the percentage of denatured proteins increases with increasing intensity of the heat treatment. The heat classification of skim milk powder is called the whey protein nitrogen index (WPNI), and is defined as milligrams of undenatured (native) whey proteins per gram of milk powder. Below the SMP heat classifications are shown as well as recommendations on the most suitable powder quality for different applications. The powder should preferably be in spray-dried form.

Skim milk powder

WPNI mg undenatured whey protein per g SMP

Low heat SMP LH >6.0

Medium heat SMP MH 1.51-5.99

High heat SMP HH <1.51

High high heat SMP HHH

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Application SMP

Pasteurized milk and cream LH-MH

UHT milk LH-MH

Yoghurt LH-MH

Cheese LH

Not only is the heat classification of importance, but also other properties such as microbiological quality, solubility, and water content. Tetra Pak can provide you with detailed quality requirements for skim milk powder intended to be used for recombined milk.

Milk fat The most common source of milk fat for recombination is anhydrous milk fat (AMF), which does not require cold storage. AMF is made of fresh raw material (milk, cream, butter) and contains at least 99.8% fat and maximum 0.1% water. To have good stability towards fat oxidation, the AMF should be prepared from good quality raw materials and be packed in oxygen-free conditions using nitrogen gas.

Butter oil can be made from stored raw material (cream, butter) of unspecified age and contains at least 99.3 % milk fat and maximum 0.5 % water. Anhydrous butter oil is made from the same raw material but contains at least 99.8 % milk fat and maximum 0.1% water.

Anhydrous milk fat Anhydrous butter oil Butter oil

Milk fat >99.8% >99.8% >99.3%

Moisture <0.1% <0.1% <0.5%

Free fatty acids (Oleic acid)

<0.3% <0.3% <0.3%

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Water Water is used in all types of recombined products. The water has to be of good drinking water quality, free from harmful microorganisms and have a low hardness. Since it is only pure water that is removed from the milk when it is dried and all minerals are left in the powder, the water used for recombination must be as pure as possible in order to not disturb the mineral balance in the recombined milk. An unusually high mineral content in the milk may cause problems during heat treatment steps or during storage. Important water quality parameters to meet in order to secure a good quality recombined milk are as below. These are the values Tetra Pak recommends.

Parameter Maximum value

Calcium, Ca 40 mg/l (100 mg/l as CaCO3)

Magnesium, Mg 25 mg/l

Total hardness 5.5 dHº

Copper, Cu 0.05 mg/l

Iron, Fe 0.1 mg/l

Chloride, Cl 100 mg/l

Sulphate, SO4 100 mg/l

Total solids 500 mg/l

pH range 7.0 – 8.0

Stabilizers and emulsifiers Stabilizers and emulsifiers include such materials as carrageenan, guar gum, sodium alginate and mono- and diglycerides of fatty acids, which help to emulsify and stabilize the fat phase, prevent sedimentation during storage and improve viscosity and mouth feel of the product. Ingredient suppliers often manufacture blends of both stabilizers and emulsifiers that are specially designed for recombined milk products. A common dosage is about 0.2% of these stabilizer/emulsifier blends.

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Best-practice production processes for recombined milk In this white paper we describe three distinct production concepts for recombining milk that are suitable for a wide range of processing needs

The first is traditional batch processing, which is currently the most common in the industry. The other two are relatively new and require more advanced equipment, but permit greater flexibility, produce higher quality products and can save on operating costs:

• Continuous single-stream blending • Continuous multi-stream blending

But before we describe these processes, it may be helpful to review just a few characteristics of dairy processing equipment, and how they affect the recombination process.

Processing factors

Hot mixing vs. cold mixing One of the most basic decisions to make is about hot mixing or cold mixing, and how it fits into your overall processes and equipment lines. At Tetra Pak we favour hot mixing because of its many advantages.

Hot mixing

• Better dissolving of milk powder

• Quicker deaeration

• Ability to emulsify oil in the mixture

• No need for pasteurization and homogenization to add oil

Cold mixing

• Lower cost for pre-heating water

• Poor dissolving of powder

• Longer deaeration time

• Need for pasteurization and homogenization to add oil

Regarding dissolving in hot vs. cold temperatures, laboratory trials with very low mixing intensity showed it took 23 hours for mixed skim milk powder to reach full dissolution at a water temperature of 23°C but only 30 minutes at a water temperature of 47°C.

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Microbiological considerations From a microbiological point of view, there are two particularly important considerations. First, the risk for microbiological growth is highest during intermediate storage of the ready mix before downstream processing and second, keeping the temperature as low as possible is optimal to the prevention of microbiological growth. However, since a temperature above 42°C is required for having milk fat in a liquid form, mixing at a less favourable temperature from a microbiological point of view is inevitable. The question therefore is: what mixing temperature is optimal to minimize the risk of microbiological growth while still achieving a stable high quality emulsion?

We have recently conducted tests to determine the answer to this question, but the results have been uncertain. What they indicate is that the optimal temperature of the final mix and its storage must be in the interval 48-50°C. As the mix temperature might drop during the mixing procedure because of the temperature of the raw materials added, adapting the temperature of the incoming hot water so the temperature of the final mix does not drop below 48°C is necessary because then undesirable bacteria may grow. They also indicate that the maximum storage time for both normal and concentrated recombined milk to be 3 hours at 50°C. This maximum storage time is based on two observations:

• The first is that concentrated recombined milk with a total solid content of 44% can be produced from water, SMP, fat and stabilizer and be stored at 50°C for 5 hours without any age thickening or microbiological growth. (Age thickening is a well known phenomenon within the dairy industry, in which the apparent viscosity of concentrated dairy solutions increases with storage time under low shear, when at elevated temperatures.)

• The second is that recombined milk with a normal concentration saw microbial growth after 3 hours of storage at 50°C.

High-performance mixing components The choice of mixer technology is all-important in order to get the right product at the right system cost. Additional investments in high-performance mixing equipment – with high-shear mixers and vacuum pumps, for example – can lead to reduced total cost of ownership, because they simplify and accelerate key procedural steps.

• Elimination of lumps in the product • Disintegration of “fish eyes" and agglomerates • Minimized hydration time • Longer production hours in pasteurizers and sterilizers • Reduced maintenance cost in homogenizer

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• Reduced off-flavour risk • Prevention of whey formation in fermented products • No sedimentation • Optimal wetting of powder • Option of adding oil during mixing • Efficient emulsification

In our discussions below, we present line solutions with mixing technologies that are based on the Tetra Pak® High Shear Mixer, which enables us to work with high-concentrate slurries.

Emulsification of fat To achieve a good emulsification of the added fat, the fat needs to be in liquid form and the temperature of the continuous phase, into which the fat will be emulsified, needs to be at a temperature above the melting point of the fat. Milk fat melts at about 42°C and hence the water needs to be at a temperature above 42°C.

The more energy that is applied i.e. the higher shear forces applied under long time the smaller the fat globules will be. Shown below is the distribution of fat globule diameters in a recombined milk prepared in a pilot Tetra Pak High Shear Mixer compared with the fat globule diameter distribution in unhomogenized raw milk. What we achieve after recombination is thus rather close to the fat globule sizes in raw cow’s milk.

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Minimization of air incorporation To prevent air incorporation during mixing, vacuum can be applied in the mixing vessel. No air will then be present inside the mixing vessel. Some air, entrapped in the powder, will however inevitably enter and be mixed into the milk. Some part of the air from the powder will be evacuated by the vacuum, but some will enter the milk. Pilot plant trials with recombined milk have shown that 2/3 of the air is removed with vacuum compared to mixing without vacuum.

Apart from the mixer itself, an air-minimizing design of the whole circulation circuit over the mixer tanks and back to the mixer again is very important for keeping the final air content low in the recombined milk.

UHT treatment (heat + homogenization) Deaeration prior to UHT treatment is optional, although recommended. This is because having air in the milk can shorten the run time of indirect UHT treatment. The deaerator should be located before the homogenizer, and the milk must be preheated to a deaeration temperature of 75-80°C.

After the optional deaeration, homogenization should take place at 75-80°C. After homogenization, the milk is heated to the sterilization temperature of 137°C and held at this temperature for 4 seconds. Cooling to reach the filling temperature of 25°C then starts.

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Other processing considerations affecting long-term storage Minimization of off-flavours and gelation problems

Enzymes that have been produced by bacteria in milk used for production of the milk powder or during storage of the recombined milk before the UHT processing may be active even in the final product after sterilization. This may result in off-flavours in the product or sweet coagulation (gelation) problems. Careful quality control of the powder used in the manufacture of recombined UHT milk and high hygiene during the recombination process is therefore needed.

Minimization of sedimentation

Another problem is sedimentation during storage. It is mainly caused by poor solubility of the milk powder; too strong heat load in the mixing stage (mainly storage at elevated temperature) or during the UHT processing; or the use of water with calcium content that is too high. To solve these problems it may be necessary to increase the homogenizing efficiency, use a suitable stabilizer, reduce the heat load during mixing and UHT processing, or soften the water.

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Production process 1 – batch production A batch production process, in which the milk fat is added batchwise at a mixing station, is the most common and used by perhaps 95% of dairies that recombine milk. A general batch recipe for milk with any fat content recombined from SMP, AMF and water can be produced according to the process and formula below.

Water is metered and heated on its way to a tank that is connected through a circulation loop with a high-shear mixer, where the dry ingredients and melted fat are added. When all the ingredients have been added, circulation stops and the product is left in the mixing tank for “hydration time” to allow the dry ingredients to dissolve completely and to achieve deaeration of the recombined milk, as well as equilibrium between all milk components. Twenty minutes of hydration is usually enough if mixing is performed at 48 to 53°C. The recombined milk is then sent for UHT processing and packaging.

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Benefits of batch processing Batch processing consistently offers the advantages of low investment costs, and is a great solution for smaller production volumes.

However, it often yields a higher total cost of ownership for higher volumes. Moreover, both the process efficiency and product quality depend on the choice of mixer.

For a comparison of the three processes, see the section on total cost of ownership.

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Production process 2 – continuous single-stream blending The configuration we show here uses OneStep technology available from Tetra Pak. This continuous single-stream blending line mixes a milk concentrate from skim milk powder and milk fat in a batch process using a Tetra Pak High Shear Mixer, followed by continuous inline dilution.

A portion of the recipe’s water is metered and heated on its way to a batch mixer. All ingredients are added in the high-shear batch mixer, resulting in a milk concentrate that is hydrated for a certain time. The milk concentrate is stored at the mixing temperature for a maximum of three hours while it is continuously sent for UHT treatment. The process begins with cooling, then dilution with water to the final milk concentration, followed by UHT treatment and packaging.

Recombination of milk concentrate with consecutive inline water dilution

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Benefits of single-stream blending A OneStep line with continuous single-stream blending has the following advantages:

• Low total cost of ownership • Low investment cost • A reduced number and size of storage tanks, which has the following benefits:

o Less CIP o Less tank preparation o Smaller line footprint o Lower maintenance costs

• High capacity • Easy product changeovers • Energy savings due to heating less liquid volume

It’s possible to upgrade from single-stream blending to a multi-stream line configuration.

For a comparison of the three processes, see the section on total cost of ownership.

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Production process 3 – continuous multi-stream blending The more advanced configuration we show here also uses OneStep technology available from Tetra Pak. This multi-stream blending line mixes a milk concentrate using a Tetra Pak High Shear Mixer in a vacuum, followed by continuous inline fat dosing and water dilution. This mixture is continuously blended, followed by further recirculation and inline high-shear mixing.

A portion of the recipe’s water is metered and heated on its way to a batch mixer. All ingredients except the fat are added in the high-shear batch mixer, resulting in a milk concentrate that is hydrated for a certain time. The milk concentrate is stored at the mixing temperature for maximum of three hours while it is continuously sent for UHT treatment. The first step is to adjust the temperature before melted fat and water are continuously blended into the final milk concentration. The milk then passes a second inline high-shear mixer to ensure a stable emulsion, before continuing to UHT treatment and packaging.

Recombination of milk concentrate with consecutive inline water dilution and fat dosing

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Benefits of multi-stream blending Like continuous single-stream blending, a OneStep line with continuous multi-stream blending also has the following advantages:

• A reduced number and size of storage tanks, which has the following benefits: o Less CIP o Less tank preparation o Smaller line footprint o Lower maintenance costs

• High capacity • Easy product changeovers • Energy savings due to heating less liquid volume

However, it also boasts several benefits above and beyond these, including:

• The lowest total cost of ownership, resulting in the highest efficiency • High accuracy, which assures consistent product quality and significant

ingredient savings • Lower product losses due to reduced hold-up volumes • and downtime • Continuous production • Increased flexibility

o Enables on-the-fly recipe changes, for example, by easily changing the fat content while continuing to use the same milk concentrate

o Makes adding additional ingredients, such as fresh milk, palm oil, chocolate, possible

For a comparison of the three processes, see the section on total cost of ownership.

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Total cost of ownership (TCO) The total cost of ownership (TCO) combines many components over the lifetime of the equipment – not just the purchase or leasing costs of equipment. And usually the largest components are operational costs, as in the diagram below. The initial investment cost is normally less than one-third of the total cost of ownership. The challenge is to find the optimal balance between all of these components.

To compare the TCO of the three processing methods we have described in this document, we established three different reference scenarios for producing recombined milk with 3.5% fat content for 50 weeks a year, using a machine capable of producing 15,000 litres/hour.

1 European cost level 2 European cost level 3 Middle Eastern cost level

Medium capacity High capacity Medium capacity

1.47 million l/week 2.295 million l/week 1.47 million l/week

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*European cost level at medium capacity ** European cost level at high capacity ***Middle East cost level at medium capacity

Note that the values shown here only cover the recombination part of the total production line.

Further cost data and calculations are available from your Tetra Pak representative.

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Environmental performance indicators The environmental benefits of continuous multi-stream blending using OneStep technology are clear when they are compared to a traditional recombined milk line with a pasteurizer. In tests run on production lines each producing about 1.5 million litres of milk weekly, we measured the following significant reductions on key environmental measures:

Water consumption -40%

Electric power -31%

Steam consumption -78%

Carbon footprint -56%

COD effluent load -66%

In this comparison, the carbon footprint includes direct and indirect electricity (pressurized air, ice water, tower water). The steam boiler efficiency was 90%, using natural gas. The CO2 equivalent for electricity was calculated using the global average value.

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Choosing equipment In general, choosing the process and equipment that is best for your recipes and production capabilities depends on a number of variables, particularly relating to volumes. Reflecting on your processes and your product mix, answering the following questions should give you sense of what your mixer needs are

• What volumes are you working with? Note that it is generally OK to use low-cost mixers for smaller volumes, but this will affect quality.

• What level of product quality does your market demand? • What running times are optimal for you? • Do you need to change between different products? • How many product changes per day? • How many product changes require cleaning? • Can you benefit from being able to change on the fly? • Can you benefit from being able to upgrade in the future? Your Tetra Pak representative can help you design or upgrade lines based on your needs.

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Tetra Pak – your dairy advisor Tetra Pak and its network of partners stand ready to assist you in many ways with your business and technical questions regarding milk processing and safety issues. Feel free to rely on these sources, or contact your Tetra Pak representative.

Dairy processing and packaging-related questions

www.tetrapak.com

More related information

http://www.tetrapak.com/processing/dairy/recombined-milk