Solid beverages are solid products made from sugar, eggs or egg products, milk or dairy products, fruit juices or edible plant extracts.

Usually the finished products are in powder, granule or block form, such as instant coffee, cream of wheat and so on.

Solid beverages are categorized according to type and are usually divided into three types: protein, regular and roasted. Compared with liquid beverages, solid beverages have the characteristics of easy to carry, unique flavor and good instant solubility.

Stability of solid beverages

In the evaluation of solid beverages, stability is an important indicator of the product. In solid beverages, especially protein-based solid beverages, destabilization is easy to occur during production and storage. There are cases in solid beverages with both suspensions and emulsions, which is a complex unstable system. Thermal sterilization or storage processes are more likely to result in destabilization of beverages, and may lead to agglomeration of proteins and solid particles, upliftment of fats, and degradation of product quality.

Denise R.P. Azeredo et al. concluded that these defects in solid beverages provide an environment for microorganisms to grow, and the problem of rancidity of beverages during the production process occurs from time to time. Therefore, improving the stability of solid beverages is the key to solid beverage production technology.

Stability characteristics are an important index for evaluating the quality of products, and to improve the stability of the products, it is necessary to control a large number of influencing factors, such as concentration, particle size, pH, electrolytes, microorganisms and so on.

The effect of concentration on the stability of solid beverages

In solid beverages, the more the number of particles per unit volume, the greater the concentration, the smaller the relative distance between particles.

The basic theory of colloidal stability holds that the interaction force between colloidal particles is mainly van der Waals gravity and electrostatic repulsion between electrically charged double layers with the same electrical properties.

At a certain concentration, when the absolute value of the repulsive potential energy of the particles of the dispersion medium is greater than the absolute value of the gravitational potential energy, the solution is stable.

On the contrary, protein particles are close to each other. Will produce cohesion, precipitation and other product instability phenomena.

The effect of particle size on the stability of solid beverages

The size of the media particle size is critical to beverage stability. If the product particle size is large, it is easy to precipitate under the action of gravity.

That is to say, for a specific kind of solid beverage powder, its viscosity and density must be, the larger the particle diameter, the greater the settling speed. The smaller the particle diameter, the smaller the settling speed.

Solid beverages occur non-rancid precipitation stratification phenomenon, the reason is that the larger particle diameter leads to a larger sedimentation velocity, thus destroying the sedimentation equilibrium to produce precipitation stratification.

Effect of pH on the stability of solid beverages

The pH value has a greater impact on protein-based solid beverages, and the key factor affecting solution stability is the isoelectric point of proteins.

When the solution pH is close to the isoelectric point of proteins, the solubility of proteins is minimized, and protein molecules aggregate to form clusters. When there is a gap between the solution pH and its isoelectric point, the protein particles at this time are in the ionic state, which can be combined with other particles in the solution to form hydrophilic colloids, and the solution is more stable.

The effect of electrolytes on the stability of solid beverages

In solid beverage solutions, the addition of electrolytes can increase the hydrophilicity and hydration of proteins, thus improving the stability of proteins.

For example, Kyeong-Ok Choi et al. concluded that the development of lipid crystals depends on thermodynamic stability. The flow of the liquid is affected by the concentration of the electrolyte, and the electrokinetic potential needs to be kept around 20 mV if the solid particles are to remain stable in solution.

Therefore, suitable electrolytes can be added to solid beverages and processing for the purpose of increasing solubility. Therefore, the addition of appropriate amount of electrolytes can improve the effect of stability.

Influence of microorganisms on the stability of solid beverages

Microorganisms are an important factor affecting the stability of solid beverages. Bacteria, yeasts and molds can cause solid beverage spoilage. Microorganisms have a particularly strong ability to reproduce, and in solid beverages containing sugars microorganisms reproduce rapidly.

They can grow well on protein-based foods even in the absence of a sugar-based carbon source present.

In the case of poor sealing or inadequate sterilization, it may cause rapid propagation of yeast fermentation, making the beverage turbid, precipitation aggregation and reduced stability. Therefore, if you want to improve the stability of solid beverages, you must first control the microbial content.