Tämä jogurtti on sopivasti hapan, mutta kahvi ei saa olla liian karvas.

Finnish simply does not have articles. There is no separate word for a/an or the.

• Tämä jogurtti can mean this yoghurt, this yogurt, this particular yoghurt, depending on context.
• Kahvi on its own can mean (the) coffee, coffee in general, or some coffee.

Definiteness is shown by:

• context,
• demonstrative pronouns like tämä (this), tuo (that), se (it / that),
• or by word order and emphasis, not by articles.

Tämä means this (one here, near me).

Rough guide:

• tämä jogurtti = this yoghurt (right here, close to the speaker)
• tuo jogurtti = that yoghurt (over there, a bit further away)
• se jogurtti = that/the yoghurt (already known from context, not necessarily visible)

In everyday speech:

• tämä often becomes tää,
• tuo often becomes toi.

In the sentence, Tämä jogurtti clearly points to a specific yoghurt the speaker has or is touching.

Sopivasti is an adverb formed from the adjective sopiva (suitable, appropriate) with the ending -sti.

• sopiva = suitable / appropriate (adjective)
• sopivasti = suitably / appropriately / to the right degree (adverb)

In Tämä jogurtti on sopivasti hapan, sopivasti modifies the adjective hapan:

• literally: This yoghurt is suitably sour
• idea: the sourness is to the right degree, not too little and not too much.

Sopiva hapan would sound odd here, because in Finnish you normally use the adverb sopivasti to talk about a degree of another quality (sour, salty, hot, etc.).

It is matching jogurtti. In a sentence like:

• Tämä jogurtti on hapan. – This yoghurt is sour.

the structure is:

• Tämä jogurtti (subject, nominative singular)
• on (verb olla, to be)
• hapan (predicative adjective, nominative singular)

With olla, adjectives that describe the subject normally appear in nominative, agreeing in number and case:

• Tämä jogurtti on hapan. – singular, nominative
• Nämä jogurtit ovat happamia. – plural, happamia = plural/partitive form, because of plural and “some/part of them” nuance

In your sentence, the yoghurt is singular and we’re just describing its quality, so hapan stays in the basic (nominative) form.

Both describe taste, but not the same taste:

• hapan = sour, like yoghurt, lemon, vinegar.
• karvas (and synonym katkera) = bitter, like strong black coffee, dark chocolate, some medicines.

So:

• sopivasti hapan = suitably sour (good amount of acidity)
• liian karvas = too bitter (too much bitterness)

You generally wouldn’t use hapan for coffee, or karvas for yoghurt, unless you’re deliberately being metaphorical.

Ei saa olla is built from:

• ei = the negative verb (3rd person singular here)
• saa = the “connegative” form of saada
• olla = to be

Here saada works like a modal verb of permission:

• Kahvi saa olla kuumaa. – The coffee may be hot / is allowed to be hot.
• Kahvi ei saa olla liian karvas. – The coffee must not be too bitter / is not allowed to be too bitter.

So in this context, ei saa olla is best translated as must not be or should not be, expressing a rule, preference, or requirement, not physical impossibility.

Finnish forms negation differently from English:

1. There’s a special negative verb ei, which is conjugated:

   • en (I don’t), et, ei, emme, ette, eivät.

2. The main verb appears in a special connegative form (often looks like the stem).

For saada (to get / be allowed):

• positive: hän saa (he/she gets / may)
• negative: hän ei saa (he/she does not get / may not)

In ei saa olla:

• ei = 3rd person singular of the negative verb
• saa = connegative of saada
• olla = infinitive “to be”

There is no structure ei on in standard Finnish; you always use ei + the appropriate verb form, not on with ei.

Both come from liika (excess, too much), but they are used differently:

• liian is used before adjectives and adverbs:

  • liian karvas = too bitter
  • liian hapan = too sour
  • liian nopeasti = too quickly

• liikaa is used more like too much with verbs or nouns:

  • Hän juo liikaa. – He drinks too much.
  • Kahvissa on liikaa sokeria. – There is too much sugar in the coffee.

So with an adjective like karvas, you need liian: liian karvas = too bitter.

Yes, Kahvi ei saa olla liian karvasta is also grammatical and actually very natural.

The difference is about nominative vs partitive in the predicative:

• liian karvas (nominative)
• liian karvasta (partitive)

Rough nuance:

• Nominative (liian karvas) can feel more like a general or “complete” quality: coffee must not be (as a thing) too bitter.
• Partitive (liian karvasta) can emphasize degree or “any amount of that quality is already too much”: coffee must not be bitter to too high a degree.

In everyday speech, with liian + adjective after a negative, many speakers prefer the partitive:

• Kahvi ei saa olla liian karvasta.

But your sentence with liian karvas is fully correct and understandable.

Finnish often uses a singular noun to talk about a thing in general:

• Kahvi on kallista. – Coffee is expensive.
• Kahvi ei saa olla liian karvas. – Coffee must not be too bitter.

Depending on context, kahvi can mean:

• coffee as a drink type in general, or
• the coffee being served right now.

Because there is no article (a/the), both readings are possible; context usually makes it clear. Here it most naturally means coffee (when I drink it) must not be too bitter.

In standard written Finnish, you almost always put a comma before mutta when it connects clauses:

• Tämä jogurtti on sopivasti hapan, mutta kahvi ei saa olla liian karvas.

Both sides (Tämä jogurtti on sopivasti hapan and kahvi ei saa olla liian karvas) are independent clauses with their own subjects and verbs, so a comma is required before mutta.

This is stricter than in English, where the comma before but is sometimes omitted in short sentences. In Finnish, comma + mutta is the norm for clause coordination.

Finnish word order is flexible, but there are clear preferences.

With adverbs like sopivasti that describe the degree of an adjective, the most natural position is directly before the adjective:

• sopivasti hapan – natural
• hapan sopivasti – possible but unusual, would sound marked or poetic in normal speech.

So:

• Tämä jogurtti on sopivasti hapan is normal everyday Finnish.
• Tämä jogurtti on hapan sopivasti would sound odd in neutral speech.

Similarly, in the second clause, liian naturally comes right before karvas: liian karvas (or liian karvasta).

In Finnish, when you use saada as a modal (may / must / be allowed to), you don’t add a separate on; you just follow it with the infinitive olla:

• Kahvi saa olla kuumaa. – Coffee may be hot.
• Kahvi ei saa olla liian karvas. – Coffee must not be too bitter.

The pattern is:

• (subject) + saada (or ei saa) + olla + adjective

If you said kahvi ei saa on, it would be ungrammatical; on already is a finite form of olla, and you can’t stack it that way after saada. The infinitive olla is the correct form after saa / ei saa.