Measurement of tannins, phenols and color in grapes and wines.
These analyses are based on the use of a spectrophotometer, UV-Vis spectral readings, capable of reading absorbance at 280 nm. If you want to invest in a spectrophotometer it is possible to buy a used one on e-bay for $250-300 USD. Phenols are an important diverse class of chemicals found in wine having a significant influence on the color and taste of red wine.
Total Wine phenols are a measurement of all colored and non-colored phenolic compounds in wine. They originate from grape skin, flesh and seed. Total wine phenol are measured in absorbance units (a.u.). Total wine tannins are a sub-class of phenols. They have the ability to precipitate proteins. Tannins play an important part of wine texture, especially astringency.
After crushing the grapes, tannins from the grape skin and seeds are extracted into the grape must. The tannins from the skins are extracted faster than those from the seeds.
Wine tannin concentration is measured in g/L in epicatechin equivalents.
Wine total pigment is a measure of total red color in the wine. It is also measured in absorbance units (a.u.). (follow the link for more details. https://www.awri.com.au/wp-content/uploads/mcp_fact_sheet.pdf )
Wine pigment is made up of free anthocyanins and pigmented tannins, both of which can also be calculated separately. A small amount of other pigmented compounds present in red wines contribute to the wine total pigment. Free anthocyanins are the colored compounds responsible for the color of red grapes. They are found in grape must, ferments and young wines. They are not stable under in alcohol, so their contribution to wine color decreases as wine ages. Anthocyanins are bleachable by SO2. Stable color originates from pigmented tannins. They are formed from the reaction of anthocyanins with tannins during fermentation and wine storage. Ninety percent of the red color of wine comes from pigmented tannins. They are not bleachable by SO2.