Food and Powder Measurement

Particle Size Distribution of Milk and Fermented-lactic Drinks

The water of milk and other fermented-lactic drinks contains many small liquid particles, or emulsions.

The particle size of emulsions in milk available in stores and supermarkets is controlled to about 1 µm by so-called "emulsification." Though, the particle size (particle size distribution) differs slightly with each manufacturer, this affects the storage period and "body" when it is drunk.

Fermented-lactic drinks used to be made for drinking by diluting a base concentrate with water. I remember that if they were left for a long time after they were stirred and mixed in a cup, they would separate into two layers, an upper layer and lower layer, and would have to be stirred and mixed again to be drunk.

In recent years, fermented-lactic drinks have appeared as canned drinks on the market, become hit products and many other similar products have come to be sold. This is because the particles in these canned fermented-lactic drinks can now be kept in a stable, small particle size state over a long period of time.

The fact itself that milk and other fermented-lactic drinks separates into two layers, an upper layer and a lower layer, does not necessarily mean that the quality of the product has dropped. However, this is a major factor contributing to how general consumers perceive product quality.

The Texture and Bite Sensation

The "texture" and "bite sensation" of food, in the broad meaning of the words, are considered to be taste.

The human tongue is quite sensitive, so much so that it is said that it can recognize particles of several 10 µm that come into contact with it. That is the "rough on the tongue" feeling. To achieve a smooth feeling, such as when eating chocolate, the size of the particles must be kept down to about 20 µm.

Which chocolate is really better for St. Valentine's day, smooth or slightly rough? Or, does this mean that how love will turn out depends on particle size distribution?

Instant coffee production methods are broadly divided into two types, spray-drying and freeze-drying. The difference between these two methods lies in the process by which moisture is removed from the coffee solution.

With the spray-drying method, coffee solution is turned into a micro mist and sprayed into hot air blast to momentarily evaporate the moisture and obtain micro coffee particles. Whereas, with the freeze-drying method, frozen coffee solution is pulverized, and moisture is removed by sublimation in a vacuum. Larger particles can be obtained by this method than by the spray-drying method since moisture is removed after freezing.

Generally, though production costs are higher with the latter method, this method is more advantageous since (1) Properties are less likely to change since the particles are not exposed to high temperature, (2) Aroma components are kept inside pores that form during freeze-drying, and (3) Particles dissolve more easily (i.e. they have a large specific surface area).

Currently, dried-food applications are extremely diverse. Measuring specific surface area and pore distribution enables assessment of these processing technologies and quality control of products.

Spaghetti is made by applying pressure to squeeze out flour dough in long thin strands. For this reason, it differs from Japanese "udon" thick wheat noodles or "soba" buckwheat noodles in that its surface is smooth and has fewer pores. In this way, surface area and pore distribution in addition to particle size distribution are related to the taste or flavor (texture) of food.