Continuous liquid-liquid extraction is a versatile, reliable and robust sample preparation technique, but there is a tendency for the solvent to make channels through the sample, causing uneven and incomplete extraction. A simple, cheap magnetic stirrer that prevents channelling improves extraction efficiency by between 2.8 and 17.6 times.
Apps, P., & Tock, M. L. A. (2005). Enhanced flavour extraction in continuous liquid-liquid extractors. Journal of Chromatography A, 1083(1–2), 215–218. https://doi.org/10.1016/j.chroma.2005.06.024