The total soluble nitrogen (TSN) content in sugar beets strongly hinders sugar extraction. Traditionally, the amount of TSN is not measured directly, but inferred from the amount of amino nitrogen (~30% of the TSN) in the beet. Betaine, the other main TSN component, accounts approximately for another 30%. Betaine also interferes with sugar crystallization, and it is a highly interesting metabolite in pharmaceutics and agronomics. The aim of this study was to develop non-invasive near-infrared (NIR) applications to measure the TSN and betaine content in beets in a fast and reliable way. Sugar beets were harvested for up to five harvest periods, and pulp samples were measured with a NIR system. Calibration models reached correlations ( R ) between laboratory and predicted values of 0.823 for TSN and 0.947 for betaine, respectively. The prediction of independent validation sets showed also high correlation coefficients for both TSN ( R  = 0.756) and betaine ( R  = 0.837). These NIR applications could be very helpful in the assessment of beet quality in breeding programs and industrial processes.