Glucans, Pectins, and Starch

Polysaccharides (glucans, pectins, or starch) may be present in juice and wines where they can contribute to difficulties in clarification, fining, and filtration. Concentrations of glucans greater than 3mg/L may create clarification and filtration problems. 

The presence of pectins (Section 17.5.3.3) is illustrated by the formation of a gel in alcoholic solution. Finally, a blue-violet color in the test tube indicates presence of starch (Section 17.5.3.4), a color that can dissipate after a few minutes. 

In a lOOmL volumetric flask, mix 1 mL 12M HCL with 90mL 95% v/v ethanol. Bring to 100 mL volume with 95% v/v ethanol. 

Transfer 10 mL of the suspect wine into a 18 x 150mm test tube and add 5 mL of acidulated ethanol. 

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When microscopically examined, this group of precipitates lack defined shape and generally assumes a color reflective of the wine. Precipitates in this category include protein and phenolics (and complexes of the two), polysaccharides (glucans, pectin, and starch), and metal casses (copper and iron). 

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