## 1 Introduction  
Nowadays, questions connected with food products, storage, and processing attract public attention. Such a situation is caused by the growing standard of people's living [1]. Contemporary lifestyle patterns influence eating habits. Today, people willingly eat instant food, because it does not need a long time for cooking or reconstitution before consumption. The most often applied method of the reconstitution of instant food is adding such liquid as water, milk, or broth [2]. Rehydration consists of a number of simultaneous processes. At the beginning, water penetrates into solid particles; then, liquid transfers between pores and penetrates into the solid matrix. At the same time, the particles disperse into the liquid. The solid particles swelling is also an important process which accompanies the rehydration [3]. The ability of dried food reconstitution depends on the extent of damage caused to the cellular structure of the dried product after different treatments to which instant food is exposed, mainly pre-drying treatments, drying, and rehydration [4; 5; 6]. There are a large volume of scientific papers describing the influences of different conditions of discussed treatments on rehydration kinetics of food products. Some examples are discussed below. [PERSON] et al. [7] reviewed the factors influencing the dehydration\(-\)rehydration mechanism of vegetables. The authors found that the structure and composition of the cell membrane and the cell wall are the most important factors affecting the drying and rehydration of plant tissue. Integrity and permeability of the cell membrane affect water transport during the dehydration and rehydration processes. The arabian side chains of the primary structure and fibers are important for water retention, whereas cell membrane disruption increases the drying rate. It can therefore be concluded that choosing the appropriate treatment methods allows for achievement of high-quality processed vegetables. [PERSON] et al. [8] studied the effect of the porous structure of dried rice noodles on their rehydration and stated that this structure influences the time of rehydration and the amount of water needed for rehydration. Different amounts of liquid were taken to process of rehydration. Table 1 presents the solid-to-liquid ratio (mass of the sample/mass of the liquid) applied in the rehydration process of the dried product. It can be seen that the volume of the discussed ratio varied from 1:333 to 1:0.512. The authors rarely explained why such amounts of liquid were taken during investigations. [PERSON] and [PERSON] [9] defined one of the rehydration characteristics as the optimum cooking time. The optimum value was determined as the minimum time needed for the potato cubes to become soft while boiling 5 g of the dried product in 100 mL of water. [PERSON] and [PERSON] [10] applied the value of the date palm fruit-to-distilled water ratio of 1:25 to minimize the influence of leaching at the process of rehydration. [PERSON] and [PERSON] [11] immersed 3 g of dried pumpkin cylinders in 1 L of distilled water in order to avoid limiting the course of rehydration because of water availability. There is also little information about the influence of the solid-to-liquid ratio on rehydration characteristics of the dried food product and, to the best of our knowledge, no information about this question for dried red beets. Red beet plantations are present in many places of the world. Edible red beet roots contain typically 4-12% of carbohydrate, 1.5% of protein, 0.8% of fiber, many important minerals (calcium, iron, magnesium, and potassium), phenolic acids, and vitamins (A, B, and C). Beetroots are rich in betanines having antioxidant capacity. Red beets may help in improving digestion and blood quality and also in protecting against cardiovascular diseases and cancer [12; 13; 14]. Taking what was written above under consideration, the aims of the present investigations were shown as follows:  
1.