Reconstitution of Powdered Milk Replacer - Particle Dispersal Test Methodology

Methodology

 

The testing procedure followed the following steps:﷯

 

1.) Two 15 gram samples of a dry milk replacer powder were weighed on a gram scale.

 

2.) Two pint glass jars were each filled with 60 grams of 110°F water.

 

3.) One powder sample was poured into each glass jar. Each jar was allowed to rest for 5 minutes to observe wetting and sinking of the powder, if any.

 

4.) The two jars were then stirred/mixed for 1 minute each with a small whisk until no solid particles were visible.

 

5.) One jar was capped and placed in a 40°F refrigerator for 8 hours to rest.

 

6.) The three sieves (shown above) were initially weighed when dry. The content of the other jar was immediately and very gently poured through the three sieves that were stacked in the order of 500µm sieve on top; 250µm in the middle; and the 125µm sieve on the bottom.

 

7.) The top sieve was sprayed with cold water to break the surface tension (see below) of the milk, such that only wet, solid particles were retained in the sieve. The top sieve was removed from the stack, and cold water sprayed through the middle sieve to break the surface tension of any liquid such that only wet solid particles would be retained in the middle sieve. Finally, the middle sieve was removed from the stack and the cold water spray was administered to the bottom sieve, allowing only wet particles <125µm to pass through the bottom sieve.

 

8.)The three sieves were then placed in a forced-air dehydrator at 135°F until the retained particles in each sieve were dry and had attained a constant weight. Each sieve was weighed on the gram scale (residue + dry sieve) and the weight was recorded. Photos were taken of the residue retained in each of the sieves (wide perspective and close-up).

 

9.) The sieves were thoroughly washed of any milk powder residue and placed in the dehydrator at 165°F until thoroughly dry. Each sieve was then weighed to insure the initial dry weight was the same (without any moisture or residue).

 

10.) After 8 hours from mixing, the previously refrigerated jar of reconstituted milk was removed and stirred/mixed with a small whisk until no solid particles were visible. It was then heated to approximately 110°F in a microwave. [Note: The use of the microwave was for test purposes only, and not recommended for use to heat or re-heat formula to be fed.]

 

11.) For this second jar, steps 6 - 9 were repeated.

 

This series of steps was then conducted for each of the individual powdered milk replacer products. Additionally, two samples were created and tested by blending two different dry milk powders together in equal parts, for purposes of step 1.) above (using equal amounts of 7.5 grams of each powder). An example of this was an equal part blend of 7.5 grams of Zoologic®33/40 and 7.5 grams of Fox Valley 32/40.

 

 

Sieve sizes

 

The sizes of the sieves used were chosen to be functional when testing the performance of a dense milk liquid while at the same time able to provide sufficient retention in order to dry and measure different sized solid milk particles. The gross dimensions of the sieves are 8" top opening diameter and bottom mesh diameter at 7", which allows for stacking of the sieves. The image below is a close-up perspective of the mesh sieves of the three sieves. The diagram following the is an accurate relative size comparison of the size particles retained by the sieves as compared to the target size of <2µm (white dot) - 10µm (dark green area) for a fully reconstituted liquid milk.