I cannot find a tea that matches your description, because the combination of Japanese style flavor and color and whole, small leaves is conflicting. I'm trying to find more information about Nepalese and Bhutanese green teas, but unfortunately they're not as well known or documented.
Perhaps we can work together to coax your memory and pin it down more?
I have four immediate questions to help pin it down more:
- Was the brewed tea yellowish at all, or a true green shade (less common)? I'm assuming you meant a true green when you said "green" but it isn't terribly specific.
- Were there any sweetness to the tea?
- What was the "nice aftertaste" you describe like?
- Can you think of any other flavor or smell descriptions that apply?
Here's what I get from your description:
The use of whole leaves, not fragments and not pearls, rule out several categories of green tea, and is probably the most useful information. It is also unusual for Japan, which tends to fragment the leaves and roll them into little spikes called sencha rolls. Many Japanese teas include parts of the tea plant other than just the leaves (buds, twigs, etc).
The lack of a yellow tinge to the brewed tea suggests a Japanese, rather than Chinese, style green tea. This is the result of cooking the leaves in processing using steam (Japan), rather than a hot pan (China), the latter of which produces "aroma molecules characteristic of roasted foods (pyrazines, pyrroles) and a yellow-green infusion" (On Food and Cooking, pg 437). If there were grassier notes, that would further suggest a Japanese tea. Ceylon green teas are kin to assam tea, and tend to be darker in color, so that's right out.
The energetic effect and bitterness suggest a higher caffeine and phenolic compound level than normal for a green tea, and rule out something like Dragonwell which is naturally quite sweet. Which is a shame, because Dragonwell is phenomenal, and varieties can have the color and leave shape you describe.
EDIT: Try sencha!
Based on your description, I think it's the best way to go forward, followed by kabusecha. "Grassy" is a descriptor usually attached to the Japanese way of preparing green teas. I always think of it as the flavor of sencha, although it applies to other Japanese green teas. I think your best bet would be ignoring the problem of leaf rolling (there may be some tea manufacturer with an eccentric way of handling it) and trying a variety of top-quality senchas to see if you can find one with a similar flavor. The best ones will be made from very young, small leaves and buds.
TL;DR = The sweet tea takes longer to cool down because there is a lot more stuff in it to get cold.
When cooling unsweetened tea, you are cooling almost pure water (the tea solids are negligible). A 12 ounce glass of unsweetened tea has about, you guessed it, 12 oz (by weight) of liquid to cool, or 340 grams (mass).
Southern-style sweet tea (if this is the "sweet tea" you are referring to), has a 2:1 ratio (by volume) of tea to sugar. A 12 ounce glass of sweet tea has 12 oz (by weight) of tea, and 5-6 ounces of sugar (by weight - 8 oz of sugar by volume = ~7 oz by weight). This puts the total weight of the beverage at 18 ounces or 510 grams (by mass).
The sweet tea, in this example, has 50% MORE mass than the unsweetened tea! This extra mass will take more time to cool down, because there is a lot more STUFF to get cold. It occupies the same volume, but there are a LOT more molecules to chill.
Compounding factors:
- Heat Capacity vs. Specific Heat: A detail to this is that a solution of sugar and water has a lower specific heat (by MASS unit) than pure water, so the total heat capacity of the sweet tea is not quite 150% of the heat capacity of the unsweetened tea, but somewhere between 100% and 150%. Intuition would put it somewhere in the 130%-140% range. Read the physics.SE question linked above for some details on that calculation. Rest assured, however, that the heat capacity of the sucrose solution is higher than pure water.
- Conductivity: I've ignored the thermal conductivity of the solution, since I'm assuming that the stirring in the tea makes the small conductivity differences between the solutions negligible, but that calculation could be done as well.
- Convection: Unstirred sweet tea will experience less convection than unstirred unsweetened tea. In the unstirred sweet tea, dense sucrose solution will remain at the bottom while the cold water from the melting ice will sit on the surface (you can actually see this visually if the tea is sufficiently colored). This slows cooling by slowing the mixing of the cold liquid with the warm liquid. In unsweetened tea the cool liquid will sink the bottom, promoting convection and self-mixing. However, convection is a side-issue to the primary point, the total heat capacity of the beverage.
And as a final note, explanations like this really make it obvious how annoying it is that US measurements use ounces for both volume AND weight.
Best Answer
Before I answer this question, the focus on small leaves and young buds is mainly relevant for green and white teas.
This category of teas are very lightly processed and are therefore very 'raw'. Using very large leaves would result in a more bitter brew. Therefore small tips and buds are the best and result in more delicate brews.
The smaller leaves are also picked in early Spring. As the temperatures are low, they grow slower and are thus richer in flavor.
These Spring buds have less supply, while there's less demand. As you can imagine, that results in higher prices.