What non-toxic non-water substances have a freezing point very close to water's?
I tried to use the curated dataset from Mathematica to answer this question.  You can ignore the following if you have no interest in Mathematica and just jump down to the end for my ideas.
The following code gets all of chemicals currently in the curated dataset and grabs the melting points and NFPA health rating.  The second line finds the chemicals with melting points between -7 and 0 degrees and the last line looks for chemicals with a health rating of 0, which is low risk.
out = {#,  ChemicalData[#,&quot;Name&quot;], ChemicalData[#,&quot;MeltingPoint&quot;],
   ChemicalData[#,&quot;NFPAHealthRating&quot;])&amp; ChemicalData[];
cull1 = Cases[out, x_ /; -7 &lt; x[[3]] &lt; 0];
cull2 = Cases[cull1, x_ /; x[[4]] == 0];

We go from about 43000 chemicals in the first list to 220 in the second and finally 6 in the last.  I'm not sure I agree with the health ratings of these compounds but here you go (melting points in parentheses):

2-methyl-2-propanethiol (-0.5)
prehnitene (-6)
trans-1,2-dichlorocyclohexane (-6)
hexadecene (-6)
trans-1,2-dibromocyclohexane (-6)
olive oil (-6)

The only chemical I would deem &quot;food safe&quot; would be the last one.  Perhaps some type of food-grade oil is the mystery substance.