J’aime le vin/j’aime les pommes. Nous achetons des pommes/de bonnes pommes/ du bon fromage/nous achetons le vin (le fromage, les fruits) au supermarché.

Whether you use the definite article (le la les) on its own or with de before it depends on the meaning you give to the noun. The fact that aimer is very often followed by the definite article without de is a question of semantics. It’s because aimer expresses a general idea. It’s the same with détester, préférer, adorer,… but you will find (probably rare) cases where those verbs are followed by the partitive article.

See https://french.stackexchange.com/questions/tagged/articles and https://french.stackexchange.com/questions/tagged/partitif

_{Note: Laure’s comments converted to an answer.}

If we consider the following sentence:

J’aime les hommes mais j’ai détesté des hommes qui méprisaient les femmes.

J’aime les hommes: hommes here is used in a generic sense, no specific group of men is determined → no partitive article.

des hommes qui méprisaient les femmes: femmes here is used in a generic sense, no specific group of women is determined → no partitive article.

J’ai détesté des hommes qui méprisaient les femmes: we use the partitive article because the relative clause qui méprisaient des femmes define the group “men”, we are no longer talking about men in general but about a specific group of men. Note also that the verb is in a past tense (ai détesté : passé composé), if the verb was in the present tense we would no longer be talking about a specific group of men but about men in general. So we need two things to determine the specificity of the group : the tense (past) and the determiner (relative clause).

The use of the partitive article is ruled by the verb as far as the concept of the verb can apply naturally to a partial quantity of the matter.

Verbs as the following are of this type.

• prendre, manger, boire, mâcher, se servir, faire cuire, préparer,…

Il boit de l’eau.• Les enfants mangent de la compote de pomme.• Elle fait cuire du riz. • Ils leur ont servi du vin. …

Other verbs cannot imply a small quantity taken as part of a whole but instead they apply to a type of thing or a specific thing and partitives are not used with those in as natural a way as those of the preceding sort; they are verbs as the following.

• aimer, haïr, apprécier, priser, avoir une préférence, connaitre,…

Ils aiment le vin.• Ils n’apprécient pas les pommes de terre.• Elle a une préférence pour le théatre.• Il ne connait pas le vin. …• Elle a aimé ce vin.• Ils apprécient ce plat de pommes de terre.

Exception for the word “monde”

• Son frère connait du monde qui s’intéresse à ça.
• (contrast) Elle connait un riz dont les grains sont plus longs.
• (apparently this is not said.) Elle connait du riz dont les grains sont plus longs.

If you want to express a partial quantity of things that are truly countable, as for instance some of the sorts of wines, or olives you use a numerical determiner.

• Ils mangent quelques unes des olives que l’on trouve ici, mais beaucoup d’autres ils ne les aiment pas.

• Ces touristes boivent peu des vins de la région.

• (contrast) Ces touristes boivent peu du vin de la région, ils consomment plutôt du vin de grand cru.

So let’s take a look at your sentences.

• J’aime le vin. correct, there is no partitive.

You must understand the rule differently: a partitive article is used only if you need to specify a small quantity out of a whole and the things can be concrete (pain, eau, cement, air, …) and abstract (liberté, bonheur, …).

• Nous achetons de fromage. *Almost correct; “fromage” is masculine, therefore you would have to say “de le”, but as this is always contracted into “du”, you say “Nous achetons du fromage.”.

• Quel fromage est-ce que vous achetez? – On achete du fromage belle Not correct; the adjective is not idiomatic; here you must say “bon” and you must place the adjective before the noun; Quel fromage est-ce que vous achetez? – On achête du bon fromage.