I am a bit puzzled. On the one hand, it is common practice among families to ask God to bless the food to be eaten. According to this very related question, the Catechism states:
every baptized person is called to be a "blessing," and to bless. Hence lay people may preside at certain blessings; the more a blessing concerns ecclesial and sacramental life, the more is its administration reserved to the ordained ministry (bishops, priests, or deacons).
Yet, according to the Catholic Encyclopedia:
[in a] strictly liturgical and restricted sense, blessing may be described as a rite, consisting of a ceremony and prayers performed in the name and with the authority of the Church by a duly qualified minister, by which persons or things are sanctified as dedicated to Divine service, or by which certain marks of Divine favour are invoked upon them.
The same article states that from very early times, the Church has considered blessing an ecclesiastical institution.
Later on, it says:
Priests, then, are the ordinary ministers of blessings, and this is only in the fitness of things since they are ordained, as the words of the Pontifical run: "ut quæcumque benedixerint benedicantur, et quacumque consecraverint consecrentur" (That whatever they bless may be blessed, and whatever they consecrate shall be consecrated). When, therefore, laymen and women are represented as blessing others it is to be understood that this is an act of will on their part, a wish or desire for another's spiritual or temporal prosperity, an appeal to God which has nothing to recommend it but the merits of personal sanctity. The ordinary greetings and salutations that take places between Christians and Catholics, leavened by mutual wishes for a share of heavenly grace, must not be confounded with liturgical blessings.
Does this mean that the blessing of food given by a priests (say, if you invite one to your house) is of a different nature that the blessing of food given by a lay person?
In my view, the different sources are, if not contradictory, rather imprecise, in particular when it comes to the comparison of the nature of both priestly and lay blessing.
Naturally, my question refers to blessings of things in which lay persons are traditionally involved (like food or family members), but not things which are traditionally reserved to priests (like holy water).