"– One lörtsy, please. – Savoury or sweet?"
Translation:– Yksi lörtsy, kiitos. – Suolainen vai makea?
This is just my opinion and could probably be more grammatically explained, but:
Here the partitive isn't used, because just one countable item is requested. "Suolainen vai makea lörtsy?".
A piece of pie is a part of a larger whole (the pie). Therefore "pala piirakkaa" (partitive). The question is then not "suolainen vai makea pala piirakkaa?" but "pala suolaista vai makeaa piirakkaa?" In short "Suolaista vai makeaa?".
You're asking for a distinct unit of something, one apple or one lörtsy or whatever, so you just use the nominative case. The partitive is used when you have some flowing, unspecified quantity of some substance or other thing that doesn't necessarily come in discrete packets. E.g. water or coffee (arguably could be either imo, in the case of a cup -- although "makea kahvi" sounds odd to me) or air or justice or laughter or whatever.
That makes complete sense. I guess my question, though, is why the inconsistency? Why is the partitive ("suolaista vai makeaa") expected for a piece of pie (in a different question), do you know? (Boarcas gave a reasonable sounding answer above. I'm assuming it's correct.)
If you consider for example the word suolainen, you have to think what does it refer to? What is the word it takes after?
I'll try to demonstrate here by putting in bold the defining word:
Suolainen pala piirakkaa
Pala suolaista piirakkaa
Pala suolaisesta piirakasta
It's not necessarily expected for a piece of pie. You can refer to the piece as a discrete unit of pie (nominative) or you can refer to you pie piece as an unspecified quantity of pie (partitive). So you can say "Here's my savory piece of pie" or you can say "Here's some savory pie". The former would be "suolainen piirakkapala" and the latter would be "suolaista piirakkaa".
So I guess the other exercise you're referring to just happened to be referring to the pie in that sort of imprecise manner. Maybe the pie piece was cut by the person themselves and it wasn't some standardized quantity like you might get in a separately packaged piece from a grocery store or something.
[EDIT: Basically I think the word "some" is key in English for communicating the same thing as the Finnish partitive. It's not "a coffee" or "a piece of pie", it's "some coffee", or "some pie". You just want some but you're not too fussy about the quantity I guess.]
It's not so uncommon, French doesn't make this distinction and I think neither does Italian.
English doesn't have it's own word for umami and most languages worldwide lack smell descriptors. It's just one of those things that doesn't seem like it's missing unless you're used to having a word for it.
"Suolainen" (nominative case) would be used for a single, countable item, while "suolaista" (partitive case) would be used for non-countable materials, or for a specified quantity of multiple items. For example: "yksi omena" (one apple), "viisi omenaa" (five apples). The partitive case is used in other situations, as well, such as certain verbs demanding a partitive object ("Minä rakastan sinua" for "I love you", the "sinua" is the partitive of "sinä" and that is because the verb "rakastaa" requires it.) Check out the rest of the comments in this thread. There's a more specific discussion of this in relation to this particular question. I hope this helps.