A jug of cocktail

The Archers (BBC Radio 4) is no stranger to drama. This week, Ambridge has been divided over whether this is grammatical: 

I'll make a jug of cocktail. 

Nouns come in two basic kinds: count and mass. The difference between them is whether they're individual things or substances (actual or metaphorical). Donkey is a count noun, because we can count three donkeys, whereas hay is a mass noun, because we can't identify three hays. Similarly, we can observe how many donkeys but not how much donkey there is round here but we can talk about how much hay there is. 

And because language is a flexible and helpful thing, we can force nouns to flip between the two types if we need them to. In what's evocatively called the 'universal grinder', we can talk about how much donkey there is if we think about it as a substance: perhaps there's been some kind of terrible accident in the stable. (Conversely, we can count hays if we're talking about different types, perhaps, at a hay convention of some kind.)

Bringing us back to cocktails, it's quite clear that specific, named cocktails work in this way, flipping between the two as needed: I drank four mojitos, or Oh no, I've spilt mojito everywhere or, relevant to this case, I'll make a jug of mojito. This might make us expect cocktail to also behave the same, but no one ever said language was logical. It seems that for at least some people (the majority of the Archers characters found the sentence ungrammatical), cocktail cannot be a mass noun. They didn't follow up with further grammaticality judgements, sadly, querying whether it's possible to say I'll make a jug of cocktails or whether you'd have to specify your cocktail... maybe it wouldn't have made good radio. 

Last follow up: can you say I'll make a jug of margarita? I think I'd be inclined to say I'll make a jug of margaritas. I wonder whether the acceptability of the construction hinges on how much we think of the cocktail as a discrete object in a particular glass with trimmings like salt rim, twist of peel, etc.