Reference for Bava Batra 191:4

ורבי יהושע בן לוי אמר כל ג' ימים האחרונים ודאי חומץ מכאן ולהלן ספק

What does this mean? — R. Johanan said, It means this: During the first three days [after the test, it is regarded as] certain wine;<span class="x" onmousemove="('comment',' For in less than three days, wine cannot turn into vinegar. Even if it be assumed that it began to turn sour immediately after the test, it would not be called 'vinegar' until full three days had elapsed. The heave-offerings given during these three days must, therefore, inevitably have been wine and, consequently, have exempted the wine in the other jugs. (V. n. 7 above). ');">⁷</span> after that, [as] doubtful.<span class="x" onmousemove="('comment',' Since it is possible that the wine began to deteriorate only three days before it was found to be vinegar, into which it may have turned just at that moment. Since the heave-offering is accordingly in doubt (V. n. 7 above). another must be given. ');">⁸</span>

Jastrow