Reconstitution of Powdered Milk Replacers - Summary Conclusions and Suggestions

As mentioned, many different factors affect the wild mammal's ability to be able to obtain more complete benefit from milk replacer, including how they are prepared. The accompanying pages describe the tests for used to better understand the reconstitution process of powdered milk replacers - which can help improve the results for the wild mammal baby fed formula. This page summarizes tests of the key steps in the process, as well as links to tests that explain the process and reasons that the steps matter. The results of these tests provide a foundation for formula preparation decisions.

It is recommended that rehabilitators read the accompanying pages in order to gain more understanding of the reconstitution process and reduce some of the difficulties experienced by rehabilitators and animals fed formula. Those issues range from difficulty dissolving the powder with clumping and separation of ingredients in a mixed formula, to undesired health problems in the animal being fed, ranging from reluctance to eat, GI upset, soft and odorous stools, diarrhea and slow growth.

If time is limited, here are the key take-aways from the research and testing:

1.) Mixing by mechanical means is essential. While some people assume the milk powders are 'instant-mix' products requiring only a quick stir, tests showed that the powders required considerable mechanical intervention to achieve an initial level of wetting and sinking. Plus, the wetting and sinking properties of the milk powders tested were all poor. The sample a milk powder shown at right is characteristic of the other products tested. The dry powder exhibits only minimal wetting and sinking (the slight cloudiness in the bottom of the jar) with almost all of the powder remaining unwetted on top of the water. 

     All products tested were stirred with a small wire whisk for 5 minutes until no visible clumps of unwetted powder were observed. While after 5 minutes of stirring the powder appeared fully dissolved, further tests would indicate that the amount of undissolved powder at this point ranged from 6% to as high as 17%.  

Fox Valley 32/40 at 3 minutes after placing powder on water.

2.) Water temperature makes a difference. Most of the tests performed and described in the accompanying pages utilized a range of water temperatures as prescribed by the standard methodology of the test performed. In order to determine if the temperature of the water at the time of mixing made a difference in final reconstitution, WildAgain tested 12 different milk replacers, involving 12 samples each, at two different water temperatures (100°F and 160°F), for a total of 288 samples. Results indicated a range of 2.5% to 3.0% improvement in reconstitution when using the 160°F water. (Specific temperature recommendations for formula preparation are described here.)

3.) Resting time post-mix provides significant improvement. Another series of tests examined the results of resting time. These tests involved stacking three sieves (filters) of decreasing sizes to catch all undissolved powder. The first test run was performed at the time of mixing ('instant-mix'), while a second run was performed after an 8 hour resting period in the refrigerator and then reheated. Both tests used the 5-minute mechanical whisking described in (1.) above.

     The results indicated that an average of 11.5% of the powder was undissolved at the time of initial mix, while only 1.0% on average was undissolved after an 8-hour rest. That results in a 91% improvement in reconstitution, which is substantial difference for the animals fed the formula.

500µm sieves -no rest at left, 8 hour rest at right.

Fox Valley 32/40 on top, Esbilac on bottom.

4.) Solubility appears generally OK; but less with casein-rich powders. An industry standard test was performed to determine solubility values (a measurement of dissolution, which is the final stage of reconstitution). As shown below, the test results showed the median value was 2.3, which seems acceptable for the grade and intended use of the products. 

     These tests were performed at 110°F water and a total resting time of only 20 minutes, according to the prescribed test procedure. The literature consistently suggests that powdered milk products will achieve a higher and more complete degree of dissolution (solubility) with hotter water temperatures and longer reconstitution (resting) time. This is especially true for the casein-rich milk replacer powders used by rehabilitators. The higher casein products tested less satisfactorily.

5.) Product freshness and cold storage are critical. All of the products tested had casein (milk protein) as ingredients. The chart at right from a research study concluded that the solubility of casein in MPC85 (Milk Protein Concentrate - 85% Protein) decreased as a function of both storage time (from initial manufacture) and storage temperature. While not shown on the chart, the study indicated that the solubility for a storage temp of 68°F decreased to 60% at 210 days (7 months).

     Rehabilitators will likely see best product performance with added attention to the embedded manufacture date in the packaging lot number to insure freshness, store the product at 0°F - 40°F, and use well before any indicated expiration date.

Closing thoughts on reconstituting powdered milk replacer

Successfully reconstituting powdered milk replacers really is much more than open, measure, add water, stir and feed. While the product packaging implies an 'instant-mix' with those few steps, test results indicate poor performance unless additional preparation steps are followed. The five key takeaways discussed above will certainly provide a more thoroughly reconstituted milk product.

WildAgain has done the literature search in the professional community. References are provided at the bottom of each web page for further reading.

WildAgin performed the various tests as used in the industry to measure reconstitution and solubility. The test methodologies used by WildAgain are provided on this website so that any rehabilitator can replicate the tests and see if they get similar results.

Lastly, consider incorporating one or more of the suggestions offered above and see if you do not see similar improvements in your substitute milk formulas.

Copyright 2002-2021. WildAgain Wildlife Rehabilitation, Inc. All rights reserved unless otherwise stated. All photo images are used with permission.