Foundational

Buying and judging green coffee

What to buy when you start roasting at home, how to store it, and what you can and cannot tell from an unroasted bean.

Why this page exists

CoffeeHQ's roasting material tells you how to take green coffee through a roast and says nothing about where it comes from or how to choose it, which is a hole the roasting programme created for itself. Green coffee is also the one part of the chain most home roasters approach with no reference points at all: a bag of unroasted beans gives away much less about itself than a bag of roasted coffee does.

What green coffee actually is

The dried seed of the coffee cherry, processed and hulled, typically around a tenth water by weight. It is hard, smells of hay or fresh grass, and tastes of essentially nothing. Every characteristic anyone associates with coffee is created during roasting from precursors in that seed — which is why roasting can lose the quality of a fine lot and cannot manufacture it in an ordinary one.

What to buy first

Something forgiving, in a quantity you will get through. Washed coffees from Central and South America are a common first choice because they behave predictably in a roaster and because their character is easy to judge — a natural process or an unusual fermentation adds a variable while you are still learning what your roaster does. Buy a small amount of two or three different coffees rather than a sack of one: comparison teaches faster than repetition, and a large sack of green bought early is usually a large sack of green still sitting there a year later.

What the information on a bag tells you

Origin, region, altitude, variety, process and screen size are the usual fields, and they carry different weights. Process is the most immediately useful for roasting, because washed, natural and honey coffees behave differently in the roaster and taste different in predictable directions. Variety and altitude are real information about what the coffee can be, and are frequently over-interpreted. Screen size is a size grading rather than a quality one — it matters to roasting because a mixed-size batch roasts unevenly, more than because larger beans are better. CoffeeHQ's grading and traceability guides cover what these terms do and do not guarantee.

What you can judge yourself

Less than you would like, and more than nothing. Look at uniformity — of size, of colour, of shape — because a batch that is visibly mixed will roast unevenly whatever you do. Look for obvious defects: black or partly black beans, insect damage, sour-looking beans, broken fragments and foreign matter. Smell it: green coffee should smell fresh and hay-like, not musty, fermented or of the sack it travelled in. What you cannot do is taste it, and no amount of inspection substitutes for roasting a small batch and cupping it.

Freshness, which works the opposite way round

Green coffee keeps far longer than roasted, and that is the main reason home roasting is practical at all — a year of coffee can be bought at once without the staling problem a year of roasted coffee would have. It is not indefinite, though. Green coffee gradually loses character and takes on a flat, woody, papery quality, and the process is accelerated by heat, humidity and light. Harvest date matters more than purchase date, and a coffee described as past crop is one from an earlier harvest, which is a statement about age rather than necessarily about quality.

Storing it

Cool, dark, dry and stable, in something that breathes a little rather than something airtight — green coffee still contains moisture and sealing it damp is worse than leaving it open. The specialist bags used in the trade are designed to hold moisture content steady, and for a home roaster a cardboard box or a cloth sack somewhere with a stable temperature is usually adequate. Avoid the two extremes: a warm loft, and a fridge, where condensation is the risk.

How much to buy

Green coffee loses roughly a sixth of its weight during roasting, so a kilo of green gives well under a kilo of roasted. Work backwards from what you actually drink — CoffeeHQ's supply planner does the arithmetic — and remember that early batches are practice rather than stock. Most people over-buy at the start and roast their way through several kilos of learning.

Sources

Technical writing on coffee roasting and extraction
Coffee Quality Institute Q Grader / cupping standards — Coffee Quality Institute (CQI)
The World Atlas of Coffee