This information comes from H. H. Scullard in his book Festivals and Ceremonies of the Roman Republic (1981).

Varro records that 'the Meditrinalia was named for mederi ["to be healed"], because Flaccus, a flamen Martialis, used to say that on this day it was the custom to pour an offering of new and old wine and to taste it in order to be healed. Many are accustomed to do this even now when they say "wine new and old I drink, of illness new and old I am cured".' Festus gives a similar quotation used on the day when the must was first tasted. Since it was clearly too early to start drinking the new wine and the real tasting and drinking took place at the Vinalia on 23 April, the emphasis of the ceremony at the Meditrinalia was perhaps on the formal tasting after a libation (indeed, despite the lack of manuscript authority, some scholars would be read libo for bibo in the formula quoted by Varro). However that may be, this was an clearly an important ceremony in early agricultural Rome, though the cultivation of the vine may not have antedated the Etruscan period. Meditrinalia may in fact derive from a non-Indo-European word, meaning the place of the ceremony, the wine-press. A goddess Meditrina is only a late Roman invention from the name of the festival, and the presiding deity was probably Jupiter, as the calendars suggest. Varro's remark that even in his day many people still 'toasted' the occasion is perhaps more likely to be true of the country rather than the town.