Taste the difference between this year's harvest and last year's harvest aged for a more rounded flavor.
20 grams of a 2014 harvested green tea
20 grams of a 2015 harvested green tea
20 grams of a 2016 harvested green tea
Tea products used will be the same product from the same original manufacturer.
It is often said that the fresher a tea leaf is, the better it tastes. This is why tea that has just been harvested, shincha or "new tea", is so highly valued.
As time passes, tea that is not stored very well will mix with the oxygen and moisture in the air and go stale within a few weeks. Temperature changes in the storage environment also play a part in this.
However, with proper storage conditions -- low humidity, low consistent temperature, airtight storage, absence of other odors -- tea leaves will age. The chemicals inside the leaf that make up its flavor will breakdown slowly without oxidizing, creating a more rounded taste. This is in fact how the leaves used to make the highest quality matcha are prepared.
Prior to the invention of temperature control technology, the process of aging tea leaves required extensive preparation as Japanese summers are hot and humid. Today, many "aged" teas are often leaves that were unsold from the previous year since temperature controlled storage used to maintain freshness acts as an environment for aging over the course of 1-2 years.