After serving 26 cups of Tea you should be able to open one of Layton's Challenges:
Tea Masters House
Professor Layton Likes Tea No 1. 1 Citrus Classic contains: Oasis Leaf - Brisk Berry Sweet - Citriona Seed.
Serve Luke Tea Blend 2 Oasis Berry ( Oasis Leaf, Brisk Berry, & Brisk Berry) during Puzzle Number 32, Its a Wrap.This information is also correct for Professor Layton and Pandora's Box.
Tea for Duke. Duke, (Boy at the gate) Likes Tea No 6. 6. Bitter Fruit: Contains: Brisk Berry, Citronia Seed and Tonic Flower Bitter
x Serve Grinko Tea Blend 12, The Layton Elixir (Joy Root Clover, Peppercherry, & Cinder Horse) during Puzzle number 94, The Mystery Cube.This information is also correct for Professor Layton and Pandora Box.
You would serve Vera (UK) aka Ilyana (USA) Tea Blend 2 Oasis Berry ( Oasis Leaf, Brisk Berry, & Brisk Berry ) during puzzle number 129, The Slobbish Mole (US) The Messy Mole (UK). Links to other questions containing useful information have been added below the answer under related questions.This information is also correct for Professor Layton and Pandora's Box.
Luke's Tea is No 2 = Oasis Berry 2 Oasis Berry Contains: Oasis Leaf - Brisk Berry Sweet x 2.
Serve Gregorio Tea 8 Clover Quencher. Clover Quencher: Smokiness and a sweetness coexist in this peculiar tea. It's perfect for quenching thirst. Brew tea 8 Clover Quencher using Brisk Berry, Joy Root Clover, & Cinder Horse When you talk to Gregorio again you must have solved the Box's Disappearance and Gregorio must not be thirsty.
Serve Tea 04 Root Remedy to Lila 4. Root remedy = Oasis leaf, Joy root clover and Tonic flower bitter.
You will see who is still thirsty as you go around each character, click onto them as you go around solving the puzzles, they will tell you what tea they require.
You must serve Hopper Tea Blend 12, The Layton Elixir (Joy Root Clover, Peppercherry, & Cinder Horse) and also must have solved Beluga's Search Mystery before the information for Puzzle number 102 Disappearing Act 2 is Revealed. A couple of helpful links have been added just below the answer under related questions.This information is also correct for Professor Layton and Pandora's Box.
Serve Tea 1 Belle Classic (Oasis Leaf, Brisk Berry, & Belle Tart Seed) to Derby for Puzzle number 89, Flower Bed Fun. A link to Puzzle number 89 has been added below the answer under related questions.For Professor Layton and Pandora's Box (UK) serve Derby Citrus Classic.
Serve Dogey Cherry Boast with the spicy kick of peppercherry that makes this Tea an ideal pick-me-up if you're feeling a little down. ( You make this tea using Oasis Leaf, Peppercherry, & Peppercherry ) In the UK Dogey is AKA as Dylan. Later in the Puzzle number 112, Turn on the Light, Joesph will be thirsty and you will Serve him Bitter Fruit, Sweet and sour with a subdued, bitter flavor. This complex tea is ideal for discerning adults. In the UK Bitter Fruit Tea is made with Citronia Seed instead of Belle Tart Seed. Both the USA and UK also add Tonic Flower and Brisk Berry.