Milk Particle Size - For Both Liquid and Dry Powder
Particles in milk?
Some people that think that milk is just a white liquid. With no solids. Yes and no. Milk is in fact a white liquid, but it also contains a variety of solid material (proteins, fats, minerals, etc.). Exactly how much solid material depends on the type of whole milk or reconstituted powdered milk. Consider the following types of milk and their respective content (% of total) of solid material:
11.7% Whole cow's milk (USDA)
13.0% Whole goat's milk (USDA)
16.8% Esbilac® (mixed with 2 parts water)
18.0% Fox Valley 32/40 (mixed with 2 parts water)
27.1% European hare mother's milk (Oftedal & Iverson)
65.7% Harp seal mother's milk (Oftedal & Iverson)
Even though this is a very small sampling of milks, it does demonstrate a wide range of water:solid ratios that exist, depending on the natural milk of the animal or of a reconstituted powdered milk substitute. For a more complete look at the differences in mother's milk, click here.
So if milk contains some or a lot of solid material, how big are the particles, even if they are hard to see?
How big is small?
Milk particles are small. Really, really tiny. The chart at right shows just how tiny they are, and compared to other objects that are also very, very tiny. Just to point out how small:
- Half of liquid milk particles are the same size as smoke particles. That's pretty tiny.
- About a third of liquid milk particles are the size of red blood cells. Larger than smoke, but still very, very small.
All in all, liquid milk particles are generally less than 2-3µm (micrometers) in size.
Dry milk powder particles are about 40 to 100 times that size, ranging from 100µm to 250µm in average size. The inset box shows the average particle sizes of some of the PetAg® and Fox Valley products as tested by the independent lab. Anyone who has used these products has seen that the PetAg® products seem to have larger powder size characteristics than the Fox Valley product powders. About twice the size. That is largely by design to make the PetAg® products reconstitute more easily, quickly and completely. This process is more fully described by following this link.
The challenge for rehabilitators who use these powdered milk replacers is to achieve a reconstituted liquid as close as possible to the same small (tiny) particle size as found in mother's milk to help the young nursing mammal baby fully digest, absorb and utilize the substitute milk.
Is it possible to get 100% of the particles to reconstitute to the appropriate size?
Probably not. But there are some formula mixing and handling techniques that can help achieve more effective results.
However the first question is to attempt to measure, or at least closely estimate, the degree to which the powders can be reconstituted. In addition, attempt to estimate the size of the particles that are being reconstituting.
The image at right shows the typical sizes of milk particles of three different types of milk - whole, semi-skimmed and skimmed. To put this into proper perspective, consider a quick look at the 'normal' size distribution of the particles that comprise milk. The image at left shows the relative distribution of particle sizes in milk with different levels of fat. As shown, since fat globules have a larger size than the casein micelles, milks with a higher fat content will have a higher percentage distribution of larger particles. This also suggests that most milk contains particles sized less than 1-2µm, with only a few fat globule clusters approaching 10µm in size. [For reference, to appreciate this small size as described above, auto emission exhaust is in the range of 1-3µm. Particles of this size are commonly measured and estimated using forward lobe light scattering and laser diffraction techniques.]
The inset box above labeled 'Reconstitution test range' shows the size of the professional lab sieves WildAgain used in determining the size of particles that would pass through sieves of various sizes. At least this would indicate what percent of the un-reconstituted, dry powder would ultimately pass through a sieve of 125µm in size.
Click here for the results of those tests for the various powdered milk replacer products.
References (not intended as an exhaustive list)
Anema, S. G., D. N. Pinder, R. J. Hunter, and Y. Hemar. Effects of storage temperature on the solubility of milk protein concentrate (MPC85). Food Hydrocolloids (2006) 20:386-393.
Baldwin, Alan J., Fonterra Research Centre, Palmerston, NZ. Insolubility of milk powder products- a minireview. Dairy Science Technology (2010) 90:169-179.
Boiarkina, I., N. Depree, W. Yu, D. I. Wilson, and B. R. Young. Rapid particle size measurements used as a proxy to control instant whole milk powder dispersibility. Dairy Science and Technology (2017) 96:777-786.
Forny, Laurent and Stefan Palzer (Food Science and Technology Department, Nestlé Research Centre, Vers-Chez-Les-Blanc, CH-1000 Lausanne, Switzerland). Wetting, disintegration and dissolution of agglomerated water soluble powders. Conference Paper · June 2009
International Diary Federation. In determination of insolubility index, Standard 129A. Brussels, IDF (1988)
Pugliese, Alessandro, Giovanni Cabassi, Emma Chiavaro, Maria Paciulli, Eleonora Carini, and Germano Mucchetti. Physical characterization of whole and skim dried milk powders. Journal of Food Science Technology (2017) 54(11):3433-3442.
Sharma, Anup, Atanu H. Jana, and Rupesh Shrikant Chavan. Functionality of milk powders and milk-based powders for end-use applications - a review. Comprehensive Reviews in Food Science and Food Safety (2012) 11:518-528.