いったん入れてからではミルクをコーヒーから分けることはできない。

once; for a moment; temporarily; one morning

to put in; to let in; to take in; to bring in; to insert; to set (a jewel, etc.); to ink in (e.g. a tattoo); to admit; to accept; to employ; to hire; to accept; to comply; to grant; to adopt (a policy, etc.); to take (advice, etc.); to listen to; to pay attention to; to include; to pay (one's rent, etc.); to cast (a vote); to make (tea, coffee, etc.); to turn on (a switch, etc.); to send (a fax); to call

from (e.g. time, place, numerical quantity); since; from (originator); by; because; since; out of (constituent, part); through (e.g. window, vestibule); after; since

be; is; indicates past or completed action; indicates light imperative

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

milk

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

coffee

to divide (into); to split (into); to part; to separate; to divide up; to classify; to sort out; to divide out; to share; to distribute; to deal out; to dish out; to distinguish; to discriminate; to differentiate (between); to break up (a fight); to mediate; to call a draw; to tie; to push one's way through (a crowd); to sell

thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as

to be able (in a position) to do; to be up to the task; to be ready; to be completed; to be made; to be built; to be good at; to be permitted (to do); to become intimate; to take up (with somebody); to grow; to be raised; to become pregnant