The Meditrinalia (from 'mederi', to heal) is celebrated on October 11 and celebrates the end of the vine harvest. The deity honoured today is most probably Iuppiter (this is based on the Fasti Amiternini), also honoured in the Vinalia of April 23. Some later sources mention a goddess called Meditrina, though this was probably a later invention. Varro [De Lingua Latina, 6.21] says the following about this day:
"Octobri mense Meditrinalia dies dictus a medendo, quod Flaccus flamen Martialis dicebat hoc die solitum vinum novum et vetus libari et degustari medicamenti causa; quod facere solent etiam nunc multi cum dicunt: 'Novum vetus vinum bibo: novo veteri morbo medeor'."
"The day of the Meditrinalia in month October was named from 'mederi' (to be healed), as Flamen Martialis Flaccus used to say that on this day it was the custom to make a libation 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'm cured.'"
Based on this testimony and on the offering to Iuppiter Dapalis described by Cato De Agricultura 132, which includes a libation of wine, we can perform a likely reconstruction of the old ritual of the Meditrinalia. For more info on the general structure of roman sacrifice see the information about the basic tools, template and guidelines for a roman sacrifice, as well as the information about posture and gesture in roman ritual.
1.Prepare a mixture of wine new and old. Note that at this time of year, the new wine mentioned by Varro is most probably grape juice or must taken from the recently harvested grapes. Accordingly, buy some mature wine and grapes, and mix one half of wine and one half of grape juice. Place the mixture in a 'patera' or similar recipient.
2. Prepare a recipient with water to stay beside you during the ritual in order for you to wash your hands. Prepare a towel as well.
3. If your place of worship has no fireplace ('focus'), you will just pour the wine on an altar or recipient prepared for the effect which you place before the place of worship.
4. Go to your place of worship in your home (lararium, shrine, or whatever). You can be helped by a few assistants who, during the ritual, will help you to wash the hands and to take the offering.
5. Cover your head. If you have a toga, you can use it to cover your head in the fashion known as 'cinctu Gabino' proper of the roman sacrificer.
6. Say the following (note that I have addressed the deity indirectly employing the 'si deus si dea' formula because it is not known with certainty which deity in honoured today):
"Si deus si dea es qui Meditrinalium tutelam habet, quod tibi hodie fieri oportet libationem vini novi et veteri, eius rei ergo macte hoc vino novo et veteri pollucendo esto."
"Be you god or goddess who has the tutelage of the Meditrinalia, as it is proper to offer to you today a libation of wine new and old, for sake of this shall you be honoured by this offering of wine new and old."
7. Wash your hands in the water prepared for the effect, and clean your hands.
8. Take the wine.
9. Pour a part of it in libation saying:
"Si deus si dea es qui Meditrinalium tutelam habet, eius rei ergo macte vino novo et veteri inferio esto."
"Be you god or goddess who has the tutelage of the Meditrinalia, for sake of this shall you be honoured by this wine new and old, which I pour in libation."
10. Note that in the previous step you have expressly noted that the wine offered is only the part poured in libation ('inferio'). You will drink the rest saying the following before drinking, as Varro teaches us:
"Novum vetus vinum bibo, novo veteri morbo medeor."
"Wine new and old I drink, of illness new and old I am cured."
11. The libation is finished. If you have not used a fireplace and just poured the wine on an altar or recipient prepared for the effect, let the wine stay before the place of worship until the next day, so that the deity may enjoy it. You should then clean it so that it does not become deteriorated and hence polluted and impure.