A concise treatment of Herbert's approach to the Eucharist can be found on the excellent Anglican Eucharistic Theology site, the work of Australian Anglican priest Dr Brian Douglas (see the link in the outer sidebar).  Herbert's views are contained in A Priest to the Temple, or the Country Parson, published after his death in 1633.  His poem, The Holy Communion, is particularly expressive in this regard.

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Herbert's poem expresses the view that Christ is present and conveyed...not in rich or golden things, but in the ordinary elements of bread and wine.  The presence of Christ is able to be fully in the person who receives ("which spread their force in every part") and to deal effectively with sin ("Meeting sinnes force and art").  The elements convey what they signify ("Onely thy grace, which with these elements comes") and are the means of grace in the life of the person who receives them.  The idea of the heavenly communion is again mentioned ("my bodie also thither") and it is in this communion that a person is joined to Christ ("Them both to be together").  Clearly the Eucharist is distinguished from other earthly food in the final verse and so the implication of the poem is that the presence of Christ in the elements is not a fleshly or immoderate presence, yet a real presence, to "which I can go."  It must be assumed then that Herbert's theology of the Eucharist is that of moderate realism.