Después de dar un sorbo al batido con la pajita, noté que llevaba demasiado azúcar.

Because después de is normally followed by an infinitive when the subject is the same as in the main clause.

• Después de dar un sorbo... = After taking a sip...
• Spanish does not say después de di

If you want to use a fully conjugated verb after después, you usually need después de que:

• Después de que di un sorbo... = After I took a sip...

That is grammatical, but in this sentence the infinitive structure is more natural and compact.

Dar un sorbo is a very common expression meaning to take a sip.

Literally, dar usually means to give, but in many Spanish expressions it works like a light verb, where the real meaning comes from the noun:

• dar un paseo = take a walk
• dar un beso = give a kiss
• dar un sorbo = take a sip

So you should learn dar un sorbo as a set phrase. You could also hear:

• tomar un sorbo = to take a sip

Both are natural.

Al is the contraction of a + el.

• a el batido → al batido

Spanish requires this contraction whenever a is followed by el.

In this sentence, dar un sorbo a algo means to take a sip of/from something:

• dar un sorbo al café
• dar un sorbo a la sopa
• dar un sorbo al batido

So al batido is both grammatically required and idiomatic.

Yes. In Spain, pajita commonly means drinking straw.

So:

• con la pajita = with the straw

This is very natural in Peninsular Spanish. In other regions, other words are common, for example:

• popote in parts of Mexico
• pitillo in some countries
• sorbete in some areas

But for Spain, pajita is the standard everyday word.

Because noté refers to a single completed moment of noticing.

• noté = I noticed
• It presents the noticing as one event that happened at that moment

That fits the sentence well: first the speaker took a sip, and then at that moment they realized something.

Compare:

• Noté que... = I noticed that...
• Notaba que... = I was noticing / I kept noticing that...

Here, the preterite is the natural choice because it is a one-time realization.

Here llevaba means something like contained or had in it.

Spanish often uses llevar to talk about what food, drinks, dishes, or products contain:

• La salsa lleva ajo. = The sauce contains garlic.
• Este pastel lleva nueces. = This cake has walnuts in it.
• El batido llevaba demasiado azúcar. = The milkshake had/contained too much sugar.

Why the imperfect?

Because the sugar content is treated as an existing state of the milkshake, not as a completed event. The speaker noticed that ongoing state at a particular moment.

• noté = the moment of noticing
• llevaba = the background condition that was already true

Could you say tenía demasiado azúcar? Yes, absolutely. That would also be natural. But llevaba is especially common when talking about ingredients or contents.

The subject is el batido, even though it is not repeated.

So the structure is:

• noté que [el batido] llevaba demasiado azúcar

In Spanish, once the noun is already clear, it is often left out. The listener understands that llevaba refers to the milkshake, not to I.

So this does not mean:

• I was carrying too much sugar

It means:

• the milkshake contained too much sugar

Because Spanish often drops subject pronouns when the verb ending already makes the subject clear.

• noté already tells you the subject is I
• So yo noté is possible, but usually unnecessary

Spanish uses subject pronouns more selectively than English. You would normally add yo only for emphasis, contrast, or clarity:

• Yo noté que llevaba demasiado azúcar, pero ellos no.

In the original sentence, leaving out yo sounds completely natural.

Both are possible, but they mean slightly different things.

• demasiado azúcar = too much sugar
• mucho azúcar = a lot of sugar

So demasiado adds the idea that the amount is excessive or more than it should be.

That matches the sentence well, because the speaker is making a negative judgment about the sweetness.

Because azúcar is usually treated as a masculine noun in modern standard Spanish:

• el azúcar
• demasiado azúcar

Even though it ends in -a, grammatical gender in Spanish does not always match the ending.

A useful rule: do not assume every noun ending in -a is feminine.

Spanish often prefers the definite article when the object is already understood from context.

So instead of saying:

• my straw
• the straw

Spanish very often chooses the straw if it is obvious which one is meant:

• con la pajita

This sounds more natural than forcing a possessive. The same thing happens with body parts, clothing, and personal objects:

• Me lavé las manos. = I washed my hands.
• Se puso la chaqueta. = He put on his jacket.

So la pajita is normal even if it is obviously the straw the speaker is using.

The first part of the sentence is an introductory time/action phrase:

• Después de dar un sorbo al batido con la pajita

The comma separates that introductory phrase from the main clause:

• noté que llevaba demasiado azúcar

This is very common in Spanish, especially when the opening phrase is a bit long. It helps readability and makes the sentence easier to process.

In theory, word placement can sometimes create that question, but in normal context the meaning is clear: it refers to how the sip was taken.

So the natural reading is:

• After taking a sip of the milkshake with the straw...

not:

• the milkshake with the straw as if the straw were just being described as part of the noun phrase

If you wanted to avoid any possible ambiguity, you could also say:

• Después de dar un sorbo con la pajita al batido...

But the original sentence is perfectly natural and easy to understand.