The HI83741-20 reagents are a set of high-quality, pre-measured chemicals designed for quick and precise colorimetric measurements. When used with the compatible HI83741 photometer, these reagents enable accurate iron analysis in various samples. The method is simple: by adding the provided wine solvent and reagent packets (HI83741A-0 and HI83741B-0) to the sample, a reaction with the iron content produces a purple tint. The intensity of this color change is directly proportional to the iron concentration, and the photometer measures this intensity to display the result in parts per million (ppm) or mg/L. This reagent kit is optimized for samples within the iron concentration range of 0.0 to 15.0 ppm.
Trace amounts of iron in wine are beneficial for promoting enzyme activity, acting as a stabilizer, and serving as a functional component of proteins. However, at higher concentrations, iron can negatively impact the wine's quality by altering its redox potential, which can favor oxidation and negatively affect sensory characteristics. Elevated iron levels can also cause instabilities, known as "casse," by forming complexes with tannins and phosphates. The most common type is 'white casse' (iron phosphate), which first appears as a milky white cloud before settling as a precipitate. The less frequent 'blue casse' (ferric tannate) can occur in white wines, especially after tannic acid additions.
Most of the iron in wine is in the ferrous Fe(II) state, with the ratio of Fe(II) to Fe(III) depending on the wine's oxidation level. If ferric Fe(III) is formed, it can bind with phosphates, leading to instability. Some winemakers add citric acid to chelate free iron if its concentration exceeds 5 mg/L. Iron typically enters wine from contact with iron-containing alloys during processing. The normal concentration of iron in must (unfermented grape juice) ranges from 1 to 5 ppm. During fermentation, a portion of the iron is naturally removed as it is absorbed by the yeast and subsequently filtered out.
