In this thesis the diffusion coefficients of coffee, caffeine and sugar were investigated.rnThe technique cmployed is Moire deflectometry. New technique of on-line monitoring ofrnthe quality of liquor in the process of manufacturing is also introduced. The diffusionrncoefficient of caffeine was found to decrease with an increase in the caffeinernconcentration at constant temperature. The diffusion coefficient of grinded and sievedrnraw coffee at a concentration of 4.11mg/ml in distilled water, at temperature of 22Â°C wasrn(3.05Â±0.16) x JO.6cm2/s. This value of diffusion coefficient is less than the value of therndiffusion coefficient of caffeine at the same concentration and temperature, in distilledrnwater, which is (6.13Â±0.16)xl0Â·6cm2/s. The main factors that are expected to haverncontributed to this difference are the fact that coffee is a mixture of many ingredients, asrnwcll as the particle size of the grinded raw coffee. Diffusion coefficient of 10% sugarrnsolution in distilled water at a room temperature of 24Â°C was also measured and the valuernfound is (6.68 Â± 0.07) xlOÂ·6cnfls. On-line monitoring of a liquid quality in the process ofrnmanufacturing is also found applicable in controlling a liquid quality. This was applied tornsugar solution that was made to flow through a horizontal diffusion tank and expectedrnresult was found. The qualitative aspect about any change in the index of refraction ofrnliquid that passes through a horizontal tank with diffusion column can easily be observedrnby a person at work; only by referring to ray deflections that correspond to the opticalrndensity of the mediumrnKey words: coffee, caffeine Moire deflectometry, diffusion coefficient, and index ofrnrefraction