Cold soluble and semi-soluble extracts
Quebracho extracts are classified according to their solubility in two main categories: cold soluble quebracho extract and semi soluble quebracho extract.
Cold soluble quebracho extracts
Are obtained by subjecting the ordinary extract to a sulphiting process which transforms the phlobaphenes into completely soluble tannins. Cold soluble quebracho extracts are the most universally known and used types. These extracts have very rapid penetration, high tannin content and a relatively low percentage of non-tannins. The rather low acid and medium salt content characterise them as mild tanning extracts (low astringency).
The semi-soluble quebracho extracts
Are special types obtained by a partial solubilisation, combined or not with a decolourisation treatment. These extracts penetrate less rapidly than the soluble types but have a greater filling power. They contain a small quantity of insolubles, while the tannin and non tannins contents are more or less the same as those of soluble extracts. The pH corresponds to the isoelectric tanning point.