This study investigated the effect of sun-dried raisins and tartaric acid (as cream of tartar) on intestinal function. 13 healthy adults consumed a low fiber, grape-free diet for three weeks. They then added 120 grams (a little over 4 ounces) of sun-dried raisins per day for another three weeks, and, lastly, substituted the sun-dried raisins with 5g of cream of tartar, approximately equivalent to the amount of tartaric acid in the sun-dried raisins, for the final three weeks. Measurements taken were transit time, fecal weight and the concentration of bile acids in the stools.

The results of this study showed that both tartaric acid and sun-dried raisins reduced transit time, but the effect was stronger for the sun-dried raisins. Fecal weight and moisture increased with the addition of raisins, but not with the cream of tartar. In addition, the participants reported greater ease of elimination when they were taking the sun-dried raisins and the cream of tartar, compared to the low-fiber, grape-free diet. The addition of sun-dried raisins reduced the concentration of bile acids, whereas the cream of tartar did not.

Another interesting finding was that sun-dried raisins, and to a lesser extent, cream of tartar, altered the concentration and ratios of bile acids in the colon in a way that, according to some research, could help prevent colorectal cancer.

This study suggests that tartaric acid works in synergy with the fiber in raisins, resulting in a healthier digestive system and colon.

Spiller GA, Story JA, Furumoto EJ, Chezem JC, Spiller M. Effect of tartaric acid and dietary fiber from sun-dried raisins on colonic function and on bile acids and volatile fatty acids excretion in healthy adults. Br J Nutr (90) 803-807, 2003.