Hi Bob,
The big "Lutheran" concern has always been an attempt to use human reason to explain and quantify a spiritual/supernatural mystery. Transubstantiation was the result of using the the "pagan" logic of Aristotle to explain these mysteries in an extra-Biblical context. Scripture speaks of the Eucharist as being both Christ's body and blood and Bread and Wine at the same time. So, one might conclude that the Lutheran position is then "Consubstantiation", however that too tries to define and quantify, and is therefore incomplete in it's attempt to explain the nature of the Eucharist.
Luther, at no time, ever stated that despite the Catholic doctrine of Transubstantiation affected the validity and efficacy of the Catholic Eucharist. In fact, it is abundantly clear to him that the Catholic doctrine was preferable to that of the reformed protestants that either denied the real presence or as the Methoidst did/do claim only a "supernatural or spiritual presence". Luther wrote that 'I would rather drink Christ's blood with the Pope than wine with Zwingli'. (exact working may be off a bit, but you get the picture).
From the Small Catechism:
It is the true body and blood of our Lord Jesus Christ, under the bread and wine, for us Christians to eat and to drink, instituted by Christ Himself.
From the Large Catechism; The Sacrament of the Altar: (spelling is old German)
"das Sacrament des Altars ... ist der ware leib und blut des HERRN Christi ynn und unter dem brod und wein..." "it is the body and blood of Christ in, with and under the bread and wine".
Based on this, one might be more inclined to say that it is 100% Christ's very body and blood and 100% bread and wine; but that too would be an attempt to over define what is truly a Divine Mystery.
As such, most Lutherans continue to elevate the host and the cup at the consecration, and many turn from the alter towards the congregation and present it to the congregation often with the words... "Behold the Lamb of God that takes away the sins of the world". Such is why the the remnants of consecrated bread and wine are consumed either immediately after the distribution by the Pastor and Assistant(s) at the altar or in the Sacristy immediately following service, or reserved for later use. While rare, the odd Lutheran Church will have a Tabernacle. Rare, in that the majority of Lutheranism hold that the adoration of the elements of the sacrament outside of the context of the Mass is not spoken of in Scripture; but the command of our Lord to "Take and eat"; "Take and Drink you all of it" seems abundantly clear.
I hope this helps.