Learn Hardcore Turkish: Limonlu su beni yazın hemen serinletiyor. - Lemon water cools me down immediately in summer.

Because beni is the accusative (direct object) form of ben (I). The verb serinletmek is transitive, so its object must take the accusative case: ben → beni. In other words, “It cools down me” → “It cools me down,” so Turkish marks “me” as beni.

Could I use bana instead of beni?

No. Bana is dative (“to me/for me”) and is used with verbs that take an indirect object (e.g., Bana limonlu su ver = “Give me lemon water”). Serinletmek takes a direct object, so you need the accusative: beni.

What exactly does serinletiyor mean and how is it formed?

Base adjective: serin = cool
Inchoative verb: serinle- = to become cool
Causative: serinlet- = to make (someone/something) become cool
Tense/person: serinlet-iyor = is cooling (3rd person singular) So serinletiyor means “(it) is cooling (someone/something) down; (it) makes (someone) feel cool.”

Why is the tense -iyor (present continuous) and not the aorist -ir?

Both are possible, with nuance:

serinletiyor: often used in colloquial Turkish for habits/general truths when there’s a time adverb like yazın; it feels more “current, experiential.”
serinletir (aorist): more “timeless/habitual” or neutral gnomic statement. So you could say: Limonlu su beni yazın hemen serinletir as well.

What do yazın and hemen modify, and where can they go?

yazın = “in (the) summer” (time adverb)
hemen = “immediately/right away” (manner/degree adverb) Natural placements:
Yazın limonlu su beni hemen serinletiyor. (time up front)
Limonlu su yazın beni hemen serinletiyor. (topic = lemon water)
Limonlu su beni yazın hemen serinletiyor. (as given) Typically, the focused element appears right before the verb; here hemen gets focus.

Does yazın mean “write!” too?

It can, but that’s a different word.

yazın (lowercase, in context) = “in summer.”
Yazın! (imperative, 2nd person plural/formal of yazmak = “to write”) means “Write!” Context and punctuation disambiguate them.

Is yazın the only way to say “in summer”?

No. Common options:

yazın = in (the) summer (neutral)
yazları = in summers/each summer (habitual)
yaz aylarında = in the summer months (more formal)
yaz mevsiminde = in the summer season (formal/literary) Using yazda is uncommon; prefer the forms above.

Does hemen ever mean “almost”?

By itself, hemen means “immediately/right away.” “Almost” is hemen hemen. Don’t confuse the two:

hemen = immediately
hemen hemen = almost/nearly

Does limonlu su mean “lemonade”?

No.

limonlu su = water with lemon (slices/juice in water)
limon suyu = lemon juice
limonata = lemonade

There’s no article like “a/the.” How would I say “a glass of lemon water”?

Turkish has no articles. Use measure words:

Bir bardak limonlu su = a glass of lemon water To specify a particular one, use a demonstrative: o limonlu su = that lemon water.

Can I drop beni?

Grammatically yes, but the meaning changes.

Limonlu su yazın hemen serinletiyor. = “Lemon water cools (people/one) quickly in summer” (unspecified object). If you mean “me,” keep beni.

Can the object pronoun come after the verb, like serinletiyor beni?

Post-verbal objects are possible for emphasis or in certain intonational contexts, but the neutral place for a pronominal object is before the verb. Beni (yazın) hemen serinletiyor sounds more natural in neutral speech.

Who is the subject here?

Limonlu su is the 3rd person singular subject. Beni is the direct object. Serinletiyor agrees with the subject (3sg) and carries the tense/aspect.

How could I say it with a reflexive structure (“I cool down”)?

Use serinlemek (to cool off oneself) and a cause clause:

Yazın limonlu su içince hemen serinliyorum. = “When I drink lemon water in summer, I cool down right away.” Here there’s no direct object; the subject is “I.”

Could I say soğutuyor or ferahlatıyor instead of serinletiyor?

soğutmak = to make cold; stronger, more physical cooling (e.g., a fridge).
serinletmek = to cool down a bit; mild, pleasant cooling.
ferahlatmak = to refresh/relieve; often used for drinks, mint, a breeze. Depending on nuance, you could say:
Limonlu su beni yazın hemen ferahlatıyor. (refreshes me)
soğutuyor would sound stronger/colder.

What’s the full morphological breakdown of the sentence?

limon-lu su: lemon-with water → “water with lemon”
ben-i: I-ACC → “me” (direct object)
yaz-ın: summer-ADV → “in summer”
hemen: “immediately/right away”
serinle-t-iyor: cool(become)-CAUS-PROG.3SG → “(it) is cooling (someone) down” (or, in context, habitual)