We study the concentration dependence of spin–lattice relaxation rates, T1−1, of glucose, fructose, sucrose and cherries by using high-Tc SQUID-based NMR at magnetic fields of ∼97 μT. The detected NMR signal, Sy(TBp), is fitted to [1 − exp(−TBp/T1)] to derive T1−1, where Sy(TBp) is the strength of the NMR signal, TBp is the duration of pre-polarization and T1−1 is the spin–lattice relaxation rate. It was found that T1−1 increases as the sugar concentrations increase. The increased T1−1 is due to the presence of more molecules in the surroundings, which increases the spin–lattice interaction and in turn enhances T1−1. The T1−1 versus degrees Brix curve provides a basis for determining unknown Brix values for cherries as well as other fruits.