Coffee does not ripen evenly
One branch will be carrying green, yellow, red and overripe cherries all at the same time. That is just how the plant works, and it is inconvenient for everybody involved.
So there are two ways to harvest. Selective picking means a person walks back to the same tree again and again across the whole season, taking only the cherries that are ready that day. Strip picking means running a hand down the branch and taking everything at once. Strip picking is faster and cheaper and it sweeps up every unripe cherry along with the good ones.
Underripe cherries taste like underripe fruit. Hard, green and astringent. And nothing further down the line removes it.
What the standard demands
The grading standards are strict here. For a lot to grade as specialty it has to have zero primary defects and no more than five secondary ones1. Five, across a whole sample. That is the margin, and it is why selective picking is not optional at this level.
Every specialty coffee you have ever enjoyed was picked by hand, many times over, by somebody who came back to the same tree.
Why the season has a shape
Coffee flowers after rain follows a dry spell. So a farm in a climate with a clear wet season and dry season gets an even flowering, which means an even harvest and a manageable picking window.
Where rain falls scattered through the year, that farm can end up with blossom, unripe green cherries and ripe red ones on the same branch simultaneously. Harvesting that is far harder and far more expensive, and it is one of the quiet reasons some origins cost more than others.
And it is not once a year everywhere
Harvests run roughly on two annual cycles depending on hemisphere and latitude, and some regions get two in a year. Colombia is the famous example, with a main crop and a smaller mitaca. Which is part of why coffee is genuinely seasonal and a roaster’s offerings move through the year.
Try this
Look for a harvest year or crop year on the next bag you buy, not just a roast date. Those two together tell you the whole shape of that coffee’s life. A fresh roast on a two year old crop is a very different thing from a fresh roast on a current one.