Isotonic solutions contain nutrients in the same concentration as the human blood. This property allows our body to quickly absorb both liquids and nutrients from the solution. Interestingly, isotonic solutions will hydrate our body faster than water! To be considered isotonic, the solution must have osmolarity of 270-330 mOsm/kg (De Fusco et al., 2019). The osmolarity of Quas is around 285 mOsm/kg, so our kvass can be called an isotonic drink. However, keep in mind that commercial kvass is a hypertonic solution because of its significantly higher sugar content!