Did the Gauls have a magic potion that made them strong?

Question

I recently listened to Purcell's "King Arthur", and at one point in the libretto, the Saxons sing of the "juice that makes the Britons bold" (at 11:40 in the linked video; the movement starts at 11:00), which immediately made me think of Asterix with the magic potion(/juice) that makes the Gauls(/Celts/Britons) strong(/bold).

Is there some underlying mythology about some Celtic potion that makes people bold/strong, or is the connection entirely apparent and spurious? (And in the case of the latter, what does the juice actually refer to?)

As an aside, I also find it interesting that they'd drink British potions in the hall of Woden. What's up with that?

The whole libretto is available here.

(Yes, this is very similar to my other question. King Arthur deals me a few surprises.)

Answer 1

The actual lyric is:

I call you all
To Woden's Hall,
Your temples round
With ivy bound
In goblets crown'd,
And plenteous bowls of burnish'd gold,
Where ye shall laugh
And dance and quaff
The juice that makes the Britons bold

To figure this out, what is Woden's Hall? The simplest source for this is Wikipedia - though it's corroborated in many places:

In wider Germanic mythology and paganism, Odin was known in Old English as Wóden, in Old Saxon as Wōden, and in Old High German as Wuotan or Wodan, all stemming from the reconstructed Proto-Germanic theonym *wōđanaz.

So, Woden's Hall is almost certainly Valhalla, a hall where the fiercest Nordic warriors would sit around waiting for Ragnarok. So what is Valhalla like, as far magic drink is like? For that, we go to the Poetic Edda:

23. Five hundred doors | and forty there are,
    I ween, in Valhall's walls;
    Eight hundred fighters | through one door fare
    When to war with the wolf they go.

24. Five hundred rooms | and forty there are
    I ween, in Bilskirnir built;
    Of all the homes | whose roofs I beheld,
    My son's the greatest meseemed.

25. Heithrun is the goat | who stands by Heerfather's hall,
    And the branches of Lærath she bites;
    The pitcher she fills | with the fair, clear mead,
    Ne'er fails the foaming drink.

_{Source: The Poetic Edda, translated by Henry Adams Bellows, p. 94}

So: the juice that makes the Briton's bold is probably referring to the mead served by the magic goat Heithrun in Odin's Valhalla.