Смородина в этом году кислее, чем прошлым летом, но варенье из неё всё равно вкусное.

Russian often uses the singular for a fruit or berry as a kind, crop, or general substance. So смородина here means currants in a general sense, not just one berry.

You can use the plural смородины, but the singular is very natural in sentences like this:

• Смородина в этом году сладкая.
• Клубника уже созрела.

So the grammar is singular in Russian, even if the best English translation is plural.

In the present tense, Russian usually omits the verb to be.

So:

• Смородина ... кислее = The currants are more sour ...
• варенье ... вкусное = the jam is tasty

Russian does use forms of быть in the past and future:

• Смородина была кислее. = The currants were more sour.
• Варенье будет вкусное. = The jam will be tasty.

Кислее is the comparative form of кислый meaning sour.

So:

• кислый = sour
• кислее = more sour / sourer

This is a very common Russian comparative pattern. Many adjectives form the comparative with -ее or -ей:

• умный → умнее
• быстрый → быстрее
• кислый → кислее

A useful point: this short comparative form does not change for gender or number:

• смородина кислее
• яблоки кислее
• лимон кислее

You could also say более кислая, but кислее sounds more natural here.

These are two different time-expression patterns.

в этом году

• uses в
  • prepositional case
• literally in this year

прошлым летом

• uses the instrumental case with no preposition
• this is a common way to say last summer, last winter, etc.

So:

• в этом году = this year
• прошлым летом = last summer

The form летом is the instrumental of лето, and прошлым agrees with it.

Russian often leaves out words that are easy to understand from context.

Here, чем прошлым летом really means something like:

• than it was last summer

A fuller version would be:

• Смородина в этом году кислее, чем была прошлым летом.

But Russian often omits была and even repeats less than English does. The listener understands that the currants this year are being compared with the currants last summer.

Because the preposition из requires the genitive case.

The pronoun refers back to смородина, which is feminine singular:

• nominative: она
• genitive after a preposition: неё

So:

• из неё = from it / from her

In this sentence it means made from it, referring to смородина.

There is also an important pronoun rule here: after most prepositions, third-person pronouns usually get an initial н-:

• у него
• к ней
• из неё
• для них

So из её would be wrong here.

Because Russian follows the grammar of смородина, and смородина is singular.

English often says currants in the plural, so a translation may use them:

• jam made from them

But in Russian the original noun is singular feminine:

• смородина
• therefore из неё

So the pronoun matches the Russian noun, not the English translation.

Here всё равно means all the same, nevertheless, or anyway.

It shows that the second part is true despite the first:

• the currants are more sour this year,
• but the jam is still tasty.

So:

• но варенье из неё всё равно вкусное means
• but the jam made from it is still tasty anyway

This is a very common expression in Russian.

Because вкусное is an adjective agreeing with варенье, and варенье is neuter singular.

So:

• вкусное варенье
• варенье вкусное

The adjective matches the noun:

• варенье = neuter singular
• вкусное = neuter singular

вкусно is different. It is usually an adverb or a predicative word:

• Здесь вкусно. = The food here is good / It’s tasty here.
• Он готовит вкусно. = He cooks well / tastily.

In this sentence, Russian wants the agreeing adjective: вкусное.

There are two main reasons.

First, there is a comma before но because но means but, and Russian normally puts a comma before it when it joins two clauses.

Second, the comparison with чем is set off here:

• кислее, чем прошлым летом

So the structure is:

• main statement
• comparative phrase
• contrast with но

That is why you see:

• Смородина в этом году кислее, чем прошлым летом, но...

Yes. For a learner, it is very helpful.

In this sentence:

• всё
• неё

both contain ё, which shows the sound and the stress.

In many everyday Russian texts, native speakers write е instead of ё, so you may also see:

• все равно
• нее

But the pronunciation is still with ё here. For learners, writing ё makes reading much easier and avoids confusion.