to the grain of
wheat, so also He compared Himself to the vine, saying (John 15:1):
"I am the true vine." But only bread from wheat is the matter of this
sacrament, as stated above (A. 3). Therefore, only wine from the
grape is the proper matter of this sacrament.

_I answer that,_ This sacrament can only be performed with wine from
the grape. First of all on account of Christ's institution, since He
instituted this sacrament in wine from the grape, as is evident from
His own words, in instituting this sacrament (Matt. 26:29): "I will
not drink from henceforth of this fruit of the vine." Secondly,
because, as stated above (A. 3), that is adopted as the matter of the
sacraments which is properly and universally considered as such. Now
that is properly called wine, which is drawn from the grape, whereas
other liquors are called wine from resemblance to the wine of the
grape. Thirdly, because the wine from the grape is more in keeping
with the effect of this sacrament, which is spiritual; because it is
written (Ps. 103:15): "That wine may cheer the heart of man."

Reply Obj. 1: Such liquors are called wine, not properly but only
from their resemblance thereto. But genuine wine can be conveyed to
such countries wherein the grape-vine does not flourish, in a
quantity sufficient for this sacrament.

Reply Obj. 2: Wine becomes vinegar by corruption; hence there is no
returning from vinegar to wine, as is said in _Metaph._ viii. And
consequently, just as this sacrament may not be made from bread which
is utterly corrupt, so neither can it be made from vinegar. It can,
however, be made from wine which is turning sour, just as from bread
turning corrupt, although he who does so sins, as stated above (A. 3).

Reply Obj. 3: The juice of unripe grapes is at the stage of
incomplete generation, and therefore it has not yet the species of
wine: on which account it may not be used for this sacrament. Must,
however, 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.
Nevertheless entire grapes ought not to be mixed with this sacrament,
because then there would be something else besides wine. It is
furthermore forbidden to offer must in the chalice, as soon as it has
been squeezed from the grape, since this is unbecoming owing to the
imp