Feed grains are typically transported in bulk and a statistically representative sample of the grain in the truckload is usually required to be taken to the laboratory for wet chemistry or at-line near infrared (NIR) spectroscopy analysis. Currently, most methodologies make use of a physical sampling probe, which mechanically or pneumatically withdraws samples from various depths. Nevertheless, not only is the implementation of this approach expensive and time-consuming, but it is also limited by low sample throughput. In this context, the authors’ group is involved in a large research and development project to find more efficient and cost-effective ways of sampling and analyzing bulk raw materials at the reception level. This work presents a piece of this research focused on the evaluation of the optical performance of two fiber-optic probes designed for automated use as immersion probes in truckloads. It is worth noting the rather different optical design of these two diffuse reflectance probes. Probe A features eight bundles (37 fibers/bundle), four for measurement and four for illumination, 0.5 m in length, and four sapphire windows located around the probe diameter. Probe B has one fiber-optic bundle for measurement (7 fibers) and one for illumination (19 fibers), 3 m in length, and a stainless-steel head with two sapphire windows. The experimental design of this laboratory study aimed at imitating the control of bulk lots of two sort of cereals (maize and wheat). For this purpose, a sample of each cereal was placed into a container (0.34 m in width, 0.4 m in length and 0.25 in height) for analysis. To avoid interferences caused by design, both probes were attached to the same Fourier transform-NIR instrument (Matrix-F, Bruker Optics), and spectra were acquired in the range 834.2–2502.4 nm using the same settings. Two different strategies for recording reference spectra were followed in each case (before the first scan and either after every measurement or after every set of 10 measurements). Noisy regions and spectral repeatability were assessed as a first step towards the evaluation of the feasibility of these probes for performing on-site analysis.