Yo no bebo cerveza, así que brindé con agua mientras ellas brindaban con vino.

Yes, Spanish often drops subject pronouns because the verb ending already shows who the subject is. So No bebo cerveza is completely natural.

Here, Yo no bebo cerveza includes yo for emphasis or contrast. It can sound like:

• As for me, I don’t drink beer
• I don’t drink beer

So yo is not required, but it helps highlight the speaker’s personal preference.

Because the sentence mixes:

• a general fact / habit: Yo no bebo cerveza = I don’t drink beer
• a specific past situation: así que brindé... mientras ellas brindaban...

The speaker is saying:

1. In general, I don’t drink beer.
2. So on that past occasion, I made a toast with water while they were making a toast with wine.

This is very common in Spanish: a present-tense statement of general truth followed by a past-tense event.

Not exactly. Brindar means to make a toast, to toast, or to raise a glass in celebration.

So:

• beber = to drink
• brindar = to toast / make a toast

That distinction matters here:

• Yo no bebo cerveza = I do not drink beer.
• Brindé con agua = I toasted with water.

The speaker is not just saying they drank water, but that they participated in the toast using water.

This is a classic Spanish tense contrast:

• brindé = preterite
• brindaban = imperfect

Here, brindé presents the speaker’s action as a completed event:
I made a toast

Meanwhile, brindaban presents the other people’s action as ongoing, in progress, or background action:
while they were toasting

So the contrast is roughly:

• brindé = the main completed action
• brindaban = the background simultaneous action

This is very natural in Spanish storytelling.

It would sound much less natural here.

With mientras, Spanish often uses the imperfect when one action is happening in the background during another event.

So:

• mientras ellas brindaban con vino = while they were toasting with wine

Using brindaron would make their action sound like another separate completed event, rather than the background action happening at the same time. In this sentence, the imperfect fits much better.

Yes, mientras brindaban con vino would also be grammatical.

Spanish often omits subject pronouns, so ellas is not necessary for grammar. It is included for clarity or emphasis, especially if the speaker wants to make the contrast clearer:

• I toasted with water
• they toasted with wine

So ellas helps underline the difference between the speaker and the other group.

Así que means so, therefore, or so then.

In this sentence, it links cause and consequence:

• Yo no bebo cerveza = I don’t drink beer
• así que brindé con agua = so I toasted with water

It is a very common connector in everyday Spanish.

Because brindar con + drink is the normal way to say to toast with a particular drink.

So:

• brindar con agua = to toast with water
• brindar con vino = to toast with wine
• brindar con champán = to toast with champagne

The preposition con shows the drink used for the toast.

Because cerveza here means beer in general, not a specific beer.

In Spanish, when talking about things in a general, non-specific way after verbs like beber, comer, comprar, etc., you often do not use the article:

• No bebo cerveza = I don’t drink beer
• Como pan = I eat bread
• Bebo agua = I drink water

If you said la cerveza, it would usually sound more specific, like:

• a particular beer
• beer as a category being contrasted in a special way
• or sometimes a more marked, contextual use

So no bebo cerveza is the normal choice.

Because mientras means while, which emphasizes that two actions were happening at the same time.

• mientras ellas brindaban con vino = while they were toasting with wine

If you used cuando, the meaning would shift more toward when, referring to a point in time rather than simultaneous background action.

Here, mientras is the best choice because the sentence is describing parallel actions.

Yes, the endings sound different, and that difference helps identify the tense.

• brindé = first-person singular preterite
  The final -é is stressed.
• brindaban = third-person plural imperfect
  The stress naturally falls on da: brin-DA-ban.

So even if you do not hear the pronouns, the verb endings tell you a lot:

• brindé = I toasted
• brindaban = they were toasting

Not in this sentence.

Here, Yo no bebo cerveza is a general statement about the speaker’s habits or preferences, so it means:

• I don’t drink beer

If you wanted I’m not drinking beer in the sense of right now, Spanish would more likely use the present progressive or a context-based present, for example:

• No estoy bebiendo cerveza
• or simply No bebo cerveza in the right context

But in this sentence, the meaning is clearly habitual/general, not temporary.

Yes, but the meaning would not be the same.

• bebí agua = I drank water
• brindé con agua = I toasted with water

The original sentence is specifically about joining in a toast, not just consuming water. So brindé con agua is more precise and fits the social situation better.