Experimental design

Twelve milk batches (milk numbers) were used in this work. They were used for different experimental purposes. Seven experimental designs were used in this work.

3.9.1 Milk Nos. 1, 2 and 3

After the pasteurized fresh whole milk (Milk Nos. 1, 2 and 3) was standardised to 3.5 % fat and 12.0 % solids-not-fat, it was used as the initial milk for UHT processing or for drying. The experiment design in Figure 3.10 consisted of three parts. The first concerned the effects of heat treatments (i.e. preheating) fresh milk prior to UHT processing. The second concerned the effects of preheating reconstituted WMP prior to UHT processing. The third concerned the effects of both pre-evaporation heat treatment (evaporator preheating) during the manufacture of SMP, and preheating the recombined milk derived from it prior to UHT processing.

Switch the feed from milk to water

Circulate water through the plant

Dismantle the high heater

Dry the plates at room temperature (18-20 °C) for 5 min

Weigh the plates

Dry the plates in an oven at 55 °C for 15 min

Weigh the plates

Chapter 3 Materials and methods 3-11

A milk number was a batch of raw fresh whole milk as delivered from which sub-batches (after pasteurization and standardization) were used in fouling trials directly, or were used to make SMP and WMP. More milk numbers were treated as replicates or more correctly, repeated measures. They were not true replicates, but using them as replicates was realistic because batch to batch variation in the composition of milk is a reality. True replicates were not possible as large quantities of milk would have had to have been stored, and because of the limited storage life of pasteurized milk.

Figure 3.10 Experimental design for fresh whole milk (FWM), recombined milk (RCB) and reconstituted milk (Recon) (Milk Nos. 1-3).

Separation

Cream Skim milk < 0.1 % fat

Standardization 3.50 % fat and 12.00 % TS UHT Preheating SMP1 - PH1 75 °C, 11 s SMP1 - PH2 85 °C, 147 s SMP1 - PH3 95 °C, 147 s SMP2 - PH1 75 °C, 11 s SMP3 - PH1 75 °C, 11 s UHT at 140 °C for 8 s Evap. preheating 95 °C, 33 s Foulingrate UHT Preheating PH1 75 °C, 11 s PH2 85 °C, 147 s PH3 95 °C, 147 s UHT at 140 °C for 8 s Fouling rate Fouling rate Homogenization 150/30 bar at 60 °C _Drying Pasteurised fresh whole milk (4 °C)

Whole milk powder

UHT Preheating PH1 75 °C, 11 s PH2 85 °C, 147 s PH3 95 °C, 147 s UHT at 140 °C for 8 s Fresh milk Reconstituted milk Chill to 4 °C Chill to 6-8°C Chill to 6-8 °C Homogenization 150/30 bar at 60 °C Evap. preheating SMP1 – 75 °C, 2 s SMP2 – 85 °C, 155 s SMP3 – 95 °C, 155 s Drying Skim milk powder

Homogenization 150/30 bar at 60 °C

Chill to 6-8 °C

Recombined milk

Reconstitute & add water to 3.50 % fat and

8.50 % solid-not-fat _{Reconstitute & add AMF to} 3.50 % fat and 8.50 % solid-not-fat

Chapter 3 Materials and methods 3-12

This experimental design was applied to three milk numbers; milk No.1 at UHT plant 1 and milk Nos. 2 and 3 at UHT plant 2. In each experiment, FWM, RCB and Recon were all derived from the same batch of fresh whole milk. Skim milk was preheated using three different evaporator preheat treatments to give SMP1, 75 °C, 2 s; SMP2, 85 °C, 155 s; SMP3, 95 °C, 155 s. Recon was evaporator preheated at 95 °C, 33 s.

The rest of the batch of standardized fresh whole milk, was not used for whole milk powder drying, was used to determine UHT-plant fouling rates for each of the three UHT preheating conditions given in Figure 3.10. Two fouling trials were carried out the same day, and two on the following day after overnight storage of the milk (at 4 °C). On the second day, one of the preheating conditions (95 °C, 147 s UHT preheat treatment) was a repeat of one of the conditions used on the first day.

In this thesis the acronym FWM (fresh whole milk) is used to identify the pasteurized, standardized and homogenized whole milk subjected to UHT preheating and the

subsequent stages of UHT processing, in order to distinguish it from recombined whole milk (RCB) and reconstituted whole milk (Recon) subjected to the same processing steps.

3.9.2 Milk Nos. 4 and 5

Pasteurised fresh whole milk (Milk Nos. 4 and 5) was dried to make whole milk powder using the process shown in Figure 3.11.

Pasteurised fresh whole milk was dried to make whole milk powder at two evaporator preheat treatments, called low-heat (LH) WMP, 75 °C, 2 s and high-heat (HH) WMP, 95 °C, 155 s.

Reconstituted LH WMP and HH WMP were each subjected to two UHT preheat treatments, 75 °C, 11 s and 95 °C, 147 s, during UHT processing.

Chapter 3 Materials and methods 3-13

Figure 3.11 Experimental design for investigation of the effect of evaporator preheating on fouling by Recon (Milk Nos. 4 and 5).

3.9.3 Milk Nos. 6 and 7

Standardised, pasteurised fresh whole milk (Milk Nos. 6 and 7) was used to investigate the effect of the order of homogenization and UHT preheat treatment on fouling rate. The process was as shown in Figure 3.12.

Pasteurised fresh whole milk (4 °C) Standardisation, 3.50 % fat and 12.00 % TS

Evap. preheating LH WMP 75 °C, 2 s HH WMP 95 °C, 155 s

Drying Whole milk powder Reconstitute & add water to 3.50 % fat and 12.00 % TS Homogenization 150/30 bar at 60 °C Chill to 6-8 °C Reconstituted milk UHT preheating 75 °C, 11 s or 95 °C, 147 s UHT at 140 °C for 8 s Fouling rate

Chapter 3 Materials and methods 3-14

Figure 3.12 Experimental design for FWM with homogenization before or after preheat treatment (Milk Nos. 6 and 7).

Pasteurised fresh whole milk was subjected to preheat treatment before or after

homogenization. Two UHT preheat treatments at 75 °C, 11 s and 95 °C, 147 s were used before or after homogenization prior to UHT processing. Fouling rate was measured for each combination of process order and UHT preheat treatment.

3.9.4 Milk No. 8

Milk No. 8 was used for trials similar to those shown in Figure 3.10, except that only two UHT preheat treatments were used, and RCB were made only from SMP1. The

experimental design is shown in Figure 3.13.

Homogenization 150/30 bar at 60 °C Preheat 75 °C, 11 s 95 °C, 147 s UHT at 140 °C for 8 s Fouling rate

Pasteurised fresh whole milk (4 °C) Standardisation

3.50 % fat and 8.50 % solids-not-fat

Preheat 75 °C, 11 s 95 °C, 147 s Homogenization 150/30 bar @ preheating temperature UHT at 140 °C for 8 s Fouling rate

Chapter 3 Materials and methods 3-15

Figure 3.13 Experimental design for fresh whole milk (FWM), recombined whole milk (RCB) and reconstituted whole milk (Recon) (Milk No. 8)

In this experiment, skim milk was evaporator preheated at 75 °C, 2 s and whole milk was evaporator preheated at 95 °C, 33 s prior to drying. FWM, RCB and Recon were subjected to two UHT preheat treatments, 75 °C, 11 s and 95 °C, 147 s, prior to UHT processing. Then, the fouling rates were measured as described in section 3.8. The high temperature heater was dismantled for deposit collection after 2 h running time after the plant had been rinsed (see section 3.7).

Separation

Cream Skim milk < 0.1 % fat

Standardization 3.50 % fat and 12.00 % TS UHT Preheating 75 °C, 11 s 95 °C, 147 s UHT at 140 °C for 8 s Evap. preheating 95 °C, 33 s

Foulingrate and analyses of deposit composition UHT Preheating 75 °C, 11 s 95 °C, 147 s UHT at 140 °C for 8 s

Fouling rate and analyses of deposit

composition Fouling rate and

analyses of deposit composition

Homogenization

150/30 bar at 60 °C _Drying Pasteurised fresh whole milk (4 °C)

Whole milk powder

UHT Preheating 75 °C, 11 s 95 °C, 147 s UHT at 140 °C for 8 s Fresh milk Reconstituted milk Chill to 4 °C Chill to 6-8 °C Chill to 6-8 °C Homogenization 150/30 bar at 60 °C Evap. preheating SMP1 – 75 °C x 2s Drying Skim milk powder

Homogenization 150/30 bar at 60 °C

Chill to 6-8 °C

Recombined milk

Reconstitute & add water to 3.50 % fat and 8.50 % solid-not-fat

Reconstitute & add AMF to 3.50 % fat and 8.50 % solid-not-fat

Chapter 3 Materials and methods 3-16

3.9.5 Milk No. 9

Pasteurised and standardized fresh whole milk (Milk No. 9) was used to study the effect of order of homogenization and UHT preheat treatment on the amount and composition of the fouling deposit in the high-temperature heater. The process was as shown in Figure 3.14.

Figure 3.14 Experimental design for FWM with preheat treatment before and after homogenization (Milk No. 9).

Pasteurised fresh whole milk was standardised and then was preheated before or after homogenization prior to UHT processing.

3.9.6 Milk Nos. 10 and 11

Two batches (Milk Nos. 10 and 11) of pasteurised fresh whole milk were processed as shown in Figure 3.15 to investigate the effect of homogenization on fouling rate, and on the amount and composition of fouling deposit in the high-temperature heater.

Homogenization 150/30 bar at 60 °C Preheat 95 °C, 147 s UHT at 140 °C for 8 s Fouling rate measurement and analyses of deposit composition

Pasteurised fresh whole milk (4 °C)

Standardisation

3.50 % fat and 8.50 % solids-not-fat

Preheat 95 °C, 147 s Homogenization 150/30 bar at 60 °C UHT at 140 °C for 8 s Fouling rate measurement and analyses of deposit composition

Chapter 3 Materials and methods 3-17

Figure 3.15 Experimental design for fresh whole milk with homogenization and no homogenization (Milk Nos. 10 and 11).

Pasteurised and standardised fresh whole milk was subjected to homogenization and no homogenization prior to UHT processing. The fouling rates were measured and the amount and composition of the deposit from the high-temperature heater measured.

3.9.7 Milk No. 2b

SMP1, 2 and 3 and WMP from Milk No. 2 were recombined to RCBs and Recon after they had been stored at 14-16 °C for 2 years in order to investigate the effect of aging on fouling rates of RCB and Recon. The experimental design is shown in Figures 3.16 and 3.17.

RCB and Recon were preheated at the different UHT preheat treatments as shown in Figures 3.16 and 3.17 prior to UHT processing. Fouling rates were measured and the amount and composition of deposits were measured.

Homogenization 150/30 bar at 60 °C Preheat 95 °C, 147 s UHT at 140 °C for 8 s Fouling rate measurement and analyses of deposit composition

Pasteurised fresh whole milk (4 °C)

Standardisation 3.50 % fat and 12.00 % TS Preheat 95 °C, 147 s UHT at 140 °C for 8 s Fouling rate measurement and analyses of deposit composition

Chapter 3 Materials and methods 3-18

Figure 3.16 Experimental design for RCB (Milk No. 2b).

Figure 3.17 Experimental design for Recon (Milk No. 2b).