Must has already the species of wine, for its sweetness ["Aut dulcis musti Vulcano decoquit humorem"; Virgil, "Georg." i, 295] indicates fermentation, which is "the result of its natural heat" ("Meteor." iv); consequently this sacrament can be made from must. ... It is forbidden to offer must in the chalice, as soon as it has been squeezed from the grape, since this is unbecoming owing to the impurity of the must. But in case of necessity it may be done: for it is said by the same Pope Julius, in the passage quoted in the argument: "If necessary, let the grape be pressed into the chalice."