Historical-critical
exegesis has shown that the manna does not, per se, seem to be a
miraculous food. What is perhaps the most widespread opinion among specialists
identifies the manna with a crystallized secretion of certain cochineal insects,
which among other things is a great source of carbohydrates (for this reason,
the Israelites of the story call it “bread”). This secretion dries rapidly,
especially in desert environments, thus easily decaying—another detail that
fits with the biblical text. Even if this were true, it would still not explain
why on the seventh day such a deterioration did not occur (unless one denies the
historicity of this detail). Thus, if one accepts a non-supernatural origin of
the manna, then one would need to perhaps accept the supernaturality of at
least two details of the story: (1) that the Israelites found it in great
abundance for forty years; (2) that it did not perish on the Sabbath and, moreover,
that on this day it did not form in the fields. It would thus remain a “bread”
that has something extraordinary about it with respect to purely biological laws.
(Mauro Gagliardi, Truth is a Synthesis: Catholic Dogmatic Theology [Steubenville,
Ohio: Emmaus Academic, 2020], 776 n. 16)