Joe, as I said off-list, I would perform the same experiment with a
12% alcohol/water mixture in a graduated liter cylinder. The
graduations were not fine enough to allow milliliter measures and so I
"borrowed" a 250-mL cylinder from work. I began this before you
posted your table.

My mixture was constituted at 78 degrees F and chilled to 50 degrees.
Like you, my measurements were of contraction. I will not go into
details here except to say they agree with your table in that the
contraction is as predicted therein (to the extent I could approximate
tenths of a milliliter), but they differ in that I began my 250
milliliters at 78 degrees.

Here is the problem I see with all of this and it is one I mentioned
in my original post to you that prompted your initial experiment. The
CRC tables all begin with the density of water being 1.000 at 4
degrees C (39.2 F), whereas we all constitute our must and the
resulting wine at a much higher ambient temperature. Our mixtures
have already expanded due to elevated temperature and so we begin with
X liters of wine under airlock at, say, 68 degrees F and then the
temperature rises. The volumetric expansion from 39.2 F, which your
table predicts, is meaningless to us. We need the expansion from 68
F. It turns out one can calculate this from your table, but it isn't
all that straightforward.

Any idea how to more easily work the problem we face in real life?

Now, having said all of that and asked my question, I still say the
solution is not to be surprised by a volume increase due to rising
temperature. Simply look at your carboys daily and when the wine
approaches the airlock remove the airlock and then some of the wine.
That is another use of a wine thief.

Jack Keller, The Winemaking Home Page
http://winemaking.jackkeller.net/