Throughout his late teens, Welch was active in the Underground Railroad that transported escaped slaves from the south into Canada. In fact, he was not the only Wesleyan Methodist connected to the “Underground Railroad.”
At age 17, Thomas Welch joined the Wesleyan Methodist Connexion, founded the same year (1843).
From its beginning, the Wesleyan Methodist Connexion strongly opposed (1) the “manufacturing, buying, selling, or using intoxicating liquors”, and (2) “slaveholding, buying, or selling” of slaves.
With the first edition of their Discipline, the Wesleyan Methodists expressly required for the Lord’s Supper that “unfermented wine only should be used at the sacrament.” This requirement was about 25 years before Welch used pasteurization. So it is clearly evident that pasteurization was not the only method used to prepare it unfermented. There were traditional methods to prepare unfermented wine (juice) for use at any time during the year, e.g. to reconstitute concentrated grape juice, or to boil raisins, or to add preservatives that prevent juice from fermenting and souring.