## 2 Materials and Methods  
Red beets (var. Wodan F1) were procured at a Warsaw market. High-quality and fresh lots were taken. Roots initial moisture content was ca. 91% w.b. (10.1 d.b.). Just before drying, the red beets were washed, peeled and cut into cubes of 10 mm thickness. The drying process was carried in a tunnel dryer. The conditions for drying were as follows: velocity (2 m/s), temperature (60 \({}^{\circ}\)C), and time (360 min). After drying, the moisture content of the dried red beets was approximately 9% w.b. (0.1 d.b.). The tunnel dryer is located in the Department of Fundamentals Engineering and Energy, Warsaw University of Life Sciences, Warsaw, Poland. The applied equipment and method of conducting the drying experiments have been described in our paper [15]. The dried red beets (the same drying conditions; three independent experiments) were mixed and then stored for further analysis in a sealed container for seven days at a temperature of 20 \({}^{\circ}\)C.  
The rehydration of the dried red beets cubes was carried out in distilled water at a temperature of 20 \({}^{\circ}\)C. The liquid was static, and its temperature remained constant during the rehydration. The process lasted 6 h. The initial mass and volume of the dried red beets cubes used in experiments were ca. 10 g and 10 cm\({}^{3}\), respectively. The solid-to-liquid ratios(dried red beets-to-distilled water ratio) at the beginning of the experiments were 1:20, 1:15, 1:10, 1:5, 1:3, and 1:1 (\(w/w\)). Mass determination  
The rehydrated cubes mass \(m\) (in g) was measured with the WPE 300 scale (RADWAG, Radom, Poland). The accuracy of measurements was \(\pm\)0.001 g.  
The dry matter \(m_{d.m. }\) (in g) was determined in accordance with the AOAC method [16]. Mass of water determination  
The mass of water in rehydrated cubes (in g) was determined from the following formula:  
\[m_{w}=m-m_{d.m.} \tag{1}\]  
Moisture content determination  
Moisture content \(M\) (in dry basis) was calculated applying Equation (2):  
\[M=\frac{m-m_{d.m.}}{m_{d.m.}} \tag{2}\]  
Volume determination  
The rehydrated cubes volume \(V\) (in cm\({}^{3}\)) was calculated according to the buoyancy in petroleum benzene with a relative error not higher than 5% [17]. The initial volume of dried red beets cubes used in experiments was ca. 10 cm\({}^{3}\). Experiments were repeated three times. The Peleg model [18] was chosen to describe the kinetics of dried red beets cubes' rehydration. The mentioned model is presented by Equation (3):  
\[X=X_{0}\pm\frac{t}{A_{1}+A_{2}t} \tag{3}\]  
where \(X_{0}\) is the initial value of the variable, \(t\) is the time, and \(A_{1}\) and \(A_{2}\) are the constants. The variable \(X\) describes the following value: rehydrated cubes mass (\(m\) in g), rehydrated cubes dry matter (\(m_{d.m. }\) in g), mass of water in rehydrated cubes (\(m_{w}\) in g), rehydrated cubes moisture content (\(M\) in d.b. ), and rehydrated cubes volume (\(V\) in cm\({}^{3}\)). It turns out from Equation (3) that when rehydration is conducted long enough, i.e., \(t\)\(\rightarrow\)\(\infty\), the equilibrium value \(X_{e}\) can be determined from the following formula:  
\[X_{e}=X_{0}\pm\frac{1}{A_{2}} \tag{4}\]  
In Equations (3) and (4), the minus sign is applied for the dry matter. The Peleg model belongs to empirical models, but its constants \(A_{1}\) and \(A_{2}\) have physical meanings. Constant \(A_{1}\), the Peleg rate constant, describes the rate of water absorption especially at the beginning of rehydration. Constant \(A_{2}\), the Peleg capacity constant, enables the prediction of the maximum capacity of water absorption. The discussed model has been very often taken for predicting the kinetics of dried biological products' rehydration. Lately, the Peleg model gave satisfactory results in describing the rehydration of dried apple slices [19], rice noodles [8], orange slices [20], pumpkin slices [21], sweet corn [22], and tomatoes [23].