Learn Hardcore Russian: Рис без соли и сахара кажется не таким вкусным. - Rice without salt and sugar seems not as tasty.

Because they’re mass nouns here (an unspecified amount of salt/sugar). After без, Russian typically uses the genitive singular for substances: без соли, без сахара. Using plurals would imply multiple types or units (e.g., different kinds of salts), which isn’t meant.

Why is it не таким вкусным (instrumental) after кажется?

With verbs like быть, казаться, стать, a descriptive predicate is often in the instrumental case to indicate a state/quality. The subject is рис (masc. sg.), so the predicate agrees in gender/number and takes instrumental:

такой вкусный (nom.) → instrumental: таким вкусным. The negation не scopes over таким here: “not so/as (that) tasty.”

Can I say кажется не такой вкусный (nominative) instead?

Not in this structure. With казаться used as the main verb, the predicate is normally instrumental: кажется не таким вкусным. You can, however, make кажется parenthetical and use a normal nominative predicate:

Кажется, рис без соли и сахара не такой вкусный.

What exactly does не таким add to the meaning?

Не таким softens the negation and implies comparison or a lower degree: “not as/so tasty,” rather than “tasteless.” It often invites an explicit comparison:

…не таким вкусным, как с солью и сахаром.

How do I state the comparison explicitly (“not as tasty as …”)?

Use как plus the comparison phrase:

Рис без соли и сахара кажется не таким вкусным, как рис с солью и сахаром.

What does кажется do here, and why does it have -ся?

Казаться is a reflexive verb meaning “to seem/appear.” The -ся is part of the verb and is not optional. It can also take a dative experiencer (to whom something seems): мне/ему/ей кажется.

How do I say “to me it seems …” in this sentence?

Add a dative pronoun:

Мне рис без соли и сахара кажется не таким вкусным. You can place the dative elsewhere too: Рис … кажется мне …

What’s the difference between не кажется таким вкусным and кажется не таким вкусным?

Рис … не кажется таким вкусным denies the seeming itself: “It doesn’t seem (so) tasty.”
Рис … кажется не таким вкусным affirms the seeming but negates the degree: “It seems not so/as tasty.” The second is softer and more comparative.

Can I drop кажется and just state the opinion?

Yes:

Рис без соли и сахара не такой вкусный. (more direct) Or use a comparative:
Рис без соли и сахара менее вкусный.

What about невкусным vs не вкусным vs this не таким вкусным?

невкусным (one word) = “tasteless/unappetizing” (strong negative): кажется невкусным.
не вкусным (two words) usually contrasts with something else: не вкусным, а пресным.
не таким вкусным = “not as/so tasty” (milder, comparative). That’s what your sentence uses.

Why not use the adverb вкусно here?

Because the subject is a noun (рис). You need an adjectival predicate agreeing with it: (не таким) вкусным. The adverb вкусно is used in impersonal constructions, e.g. Есть рис без соли и сахара невкусно (“Eating rice without salt and sugar is not tasty”), which is a different structure.

Is the word order fixed? Can I move the phrase around?

Word order is flexible. All of these are natural:

Без соли и сахара рис кажется не таким вкусным.
Рис без соли и сахара кажется не таким вкусным.
Рис кажется не таким вкусным без соли и сахара. The focus changes slightly with placement, but the meaning stays the same.

Do I need a comma before or after кажется?

In your sentence, кажется is the main verb—no commas.
If кажется is parenthetical (“it seems”), use commas: Кажется, рис без соли и сахара не такой вкусный.

Why does сахар become сахара? Is that plural?

Here сахара is genitive singular (required by без). Note: сахара can also be nominative plural in other contexts (“different sugars”), but after без you know it’s genitive singular.

What are the genders of the nouns, and how does agreement work here?

рис: masculine (subject)
соль: feminine
сахар: masculine Agreement matters for the predicate adjective: because рис is masculine singular, you use masculine singular instrumental таким вкусным after кажется.

Why is it без соли и сахара (with “and”), not something like “or”?

Russian uses без X и Y to mean “without X and Y” (i.e., with neither of them). It’s the normal way to say “without salt or sugar” in English. You can repeat без for emphasis: без соли и без сахара.

Can I use ни … ни … with без?

Not together. Use either:

без соли и сахара (standard with the preposition) or, in a negative clause:
В рисе нет ни соли, ни сахара. (no preposition; “there is neither salt nor sugar in the rice”)