Because it's çorbaYI with the accusative ending, and (to a first approximation) only definite objects get marked with the accusative.
So if you see an accusative ending, it'll be definite: either "the" or some other determiner such as "that" or "my" will be appropriate in the English translation.
- they are drinking = içiyorlar
- they drink = içerler
Simple present ("They are drinking"):
- Verb stem + i (4-way vowel harmony) + yor + personal suffix
- iç + i + yor + lar
Note: if verb stem ends in a vowel, it will be REPLACED by -i (with vowel harmony). For example: ödemek (to pay) = ödüyorlar (they are paying)
Aorist Tense ("They drink"):
These are a little more complicated because it depends on how many syllables are in the verb stem.
- 1 syllable verb stem + ar (2-way harmony) + personal suffix
- iç + er + ler
- 2 or more syllable verb stem + ir (4-way harmony) + personal suffix
- öğren + ir + ler ("they learn")
Note: if the verb stem ends in a vowel, we just add -r + personal suffix. Ex. ödemek (to pay) = öderler (they pay)
Maybe "tuzlu" is an adverb here, since it comes after the noun. The first TIPS discussion on adjectives says that they "must always come before the nouns that they modify when they operate as modifiers." Or maybe I should relax a little about classification and rules and just observe what the language does.