One way to picture taster: one mouthful, taken before the rest. Around that single mouthful stand three things — the person who takes it and judges, the little cup or spoon it sits in, and the small portion handed to you so you can decide whether you want the whole. Taste plus -er lets the word land on any of the three, and the sentence around it tells you which one is meant.
From the word’s history
The supplied source records taster as coming from Middle English taster, equivalent to taste plus the ending -er. That ending can attach to a person or to a thing, which is why the same word covers the one who tastes and the cup the taste is poured into.
來源資料記的是：taster 來自中古英文 taster，相當於 taste 加上字尾 -er。這個字尾可以落在人身上，也可以落在東西上。所以同一個字既能指嚐的人，也能指盛那一口用的小杯，這一點在組字的方式裡就已經留好了空間。
Wiktionary entry supplied in the evidence packet (source_ref kaikki:3f6f69a190036ae4:625401569)
登入就可以看每一支怎麼連回核心畫面。