I strictly play 5th edition, having only been playing Ars Magica for just shy of 3 years. However, I was perusing an older book, The Order of Hermes (1st ed.?), and in the Jerbiton chapter it had a spell called the Communion of Peace, which allows the magus to cast the spell on something like food, wine or candles to make all who drink/eat/inhale from that item to become more agreeable, even if they hate one another.
Is this spell able to be made in 5th ed. with basic rules, or do you need a mystery? I know that Shape of the Woodland Prowler uses an object (wolf skin) to "activate" the spell. Does it work the same way? Can you make any spell contingent on the use of an item?
The vanilla way to do it is Watching Ward (ArM5 p.162). This is a ritual, though, so that could end up being a lot of rituals. Mercurian Magic along with Imbued with the Spirit of Vim could let you pull it off many times without going broke, though that then ceases to be vanilla.
It could be done with Tethering (see HoH:TL, Mercere section). That could be available via Mutantum Magic, having Tethered Magic (directly or through Tamed Magic), or using the Tethered Casting option for Spell Mastery. Although, I think it would just trigger on being touched as opposed to being consumed.
Hmm. Not without at the verrry least a storyguide approving this with
But it would rather look like a new type of spell target to me, needing a Minor Hermetic Virtue and a good background story to use it. If you call the Virtue Feast Magic, it might perhaps fit with HoH:S p.54 The Gastronomers of House Jerbiton.
As is, I don't think it is feasible: imbuing a magical effect into an objet in such a way that people touching/consuming said object is not something that can be done short of an enchantment. And even for an enchantment, it would need some "creativity".
Within purely the core rulebook, I would look at making a charged item that have the proper ReMe (Range: touch) effect in it. The item, whether an loaf of bread or a jar of wine, can be divided into a number of servings equal to the number of charge it contains. Those consuming the item are affected by the effect. It takes a season to prepare.
Looking outside of the core rulebook, the Sensory magic of House Bjornaer would allow to affect all who are hearing the mage for the duration of the spell. The difference with a Range: Voice is that the mage cast the ReMe on himself with the Sound Target (p28, Mystery Cult), equivalent to Structure and anybody hearing him for the duration of the spell is affected, whereas a Range of Voice means that you are affecting targets only at the moment you are casting it - late comers won't be affected as the casting is over.
The option proposed by One Shot (Feast Magic) would be an adaptation of Sensory magic of "Taste target" instead of Sound Target. However, there would be a major improvement over the Bjornaer Sensory magic since Sensory magic target is always centered on the mage, whereas this Feast Magic would be imbuing an item.
You might be able to pull it off with Performance magic, as long as the mage keeps "performing" to maintain the spell.
Could the food be tainted with a specific toxin which tends the imbibers to be more passive and calm? It's not the Mentem effect desired but might be close enough.
Rather than a spell which uses a new complex target discussed (which I can't rationalise in standard Hermetic magic), instead it's a CrAq toxin with that effect. If a toxin can cause harm, put somebody to sleep, then why not calm them?
Edit: or a MuHe/Aq effect?