First rule of science - skepticism. Here is how this sort of study funded by grape growers works. You compare a tablet of red wine (resveratrol) which lacks required dosage; or which has required dosage but is not digestible in tablet form; with grade powder which mixed with water is easily digestible. You get the predictable result: red wine (reserveratrol) tablets don’t work but grape powder does. This tells us nothing and is a scientific trick. Liquid supplements work best, followed by capsules, followed by tablets. Resveratrol supplements come in many forms - some are liquid and are encapsulized in a medical lab under vacuum to preserve potency, some are powder put in a capsule with alcohol, some are hard tablets which may just pass through your digestive system. If you buy resveratrol without alcohol and stabilized in an air tight capsule you will get the true potency. I found it easier and more certain than carrying bottle of grape juice around with me.
How was it established that the tablet used in the study is not digestible?