Abstract The interaction of tannins from different sources (grape skin, grape seed and wine) with bovine serum albumin (BSA) was studied using a continuous flow method with nephelometric detection. The tannin samples were mixed in a reaction chamber with increasing BSA concentration and the resulting tannin–BSA insoluble aggregates passed through a flow cell where the turbidity was monitored. Based on this technique, the tannin specific activity (TSA) of wine can be directly determined from different wine flows without previous dilutions or any other treatment. The maximum amount of insoluble aggregates formed with BSA and wine or grape skin tannins seemed to remain constant even with the addition of an excess of protein, whereas a decrease in the amount of insoluble aggregates with an excess of BSA was observed in the case of grape seed tannins. It should be noted that BSA was used in these experiments as a model protein and only as an analytical reagent since bovine additives are not allowed in wine.