Key Coffee Terms Explained: From Defects to Frost Damage

Ever wondered why your cup of coffee tastes off, or what those industry terms really mean? Whether you're a home roaster or just curious about coffee lingo, understanding key terms like 'defects,' 'screen size,' and 'frost damage' can transform how you evaluate and talk about coffee.

This guide covers seven essential coffee terms every enthusiast should know—from identifying problematic beans to understanding how weather and processing shape the final cup. We break down each concept with precise details, including numbers, ratios, and historical context.

What Are Coffee Defects?

Defects refer to flawed green coffee beans mixed in with good ones. These include moldy beans, dead beans, black beans, underripe beans, and fermented beans. If these aren’t hand-picked and removed before or after roasting, they’ll ruin the coffee’s flavor. Even a few defects can drastically alter taste profiles.

How Are Coffee Beans Classified by Origin?

The New York Futures Exchange categorizes coffee into four types based on origin. One of these is 'Colombian Bright-Type Coffee,' which includes beans from Colombia, Kenya, and Tanzania. The other three categories are washed (other bright-type), unwashed (non-washed Arabica), and Robusta. Global coffee futures trading revolves around these four classifications.

What Is Coffee Leaf Rust?

Coffee leaf rust is a disease that commonly affects coffee trees in rainy regions. It occurs when fungus attaches to the leaf’s stomata, creating spots. Highly contagious, it once wiped out all Arabica plantations in Sri Lanka (formerly Ceylon) and Indonesia, forcing a switch to the more disease-resistant Robusta variety.

How Does Coffee Bean Screening Work?

Screening sorts green coffee beans by size using perforated sieves. The holes are measured in 1/64-inch units. For example, an 18/64-inch sieve retains beans larger than 18/64 inch and lets smaller ones pass. The higher the sieve number, the larger the beans. This process ensures uniformity in roast profiles and helps identify physical bean quality.

What Defines Specialty Coffee?

There’s no strict global definition, but specialty coffee generally refers to beans with distinct, memorable flavors that mark them as high quality. Standards vary by country and specialty coffee association. Historically, terms like 'Old Number Coffee' and 'Platinum Coffee' also fell under this umbrella.

Why Do Coffee Farmers Plant Shade Trees?

Shade trees, often bananas or mangoes, are planted among coffee plants to protect them from direct sunlight. They also help mitigate risks from frost and pests. This traditional practice supports healthier coffee growth and can improve cup quality by regulating microclimates.

What Happens During a Coffee Frost?

Frost damage occurs when freezing temperatures harm coffee trees. A notable example is the 1975–76 frost in Brazil’s Paraná state—the worst in 50 years—which destroyed 915 million coffee trees. Brazil, which then accounted for a third of global production (25 million bags), saw output plummet to 8.2 million bags. This caused international green coffee prices to skyrocket from around 60 cents to $3.36 per pound, a historic high.

What Is Double Roasting?

Double roasting means roasting coffee beans twice. The process involves removing the beans from the roaster, cooling them, and roasting them again. This can address issues like uneven drying or smooth out rough bean surfaces. However, while it may improve appearance, double roasting often results in a duller flavor profile.

Frequently Asked Questions

What counts as a coffee defect?

Coffee defects include moldy beans, dead beans, black beans, underripe beans, and fermented beans. These flawed beans, if not removed before or after roasting, can significantly degrade the flavor of the final cup.

How are coffee beans sized for roasting?

Coffee beans are sorted by size using screens with holes measured in 1/64-inch units. An 18/64-inch sieve, for instance, keeps beans larger than 18/64 inch. Higher sieve numbers mean larger beans, ensuring more uniform roasting.

What is the New York Futures Exchange coffee classification?

The exchange classifies coffee into four types: Colombian Bright-Type (including Colombia, Kenya, Tanzania), washed (other bright-type), unwashed (non-washed Arabica), and Robusta. Futures trading uses these four categories.

What causes coffee leaf rust and what are its effects?

Coffee leaf rust is a fungal disease that thrives in wet conditions, attacking coffee leaves and causing spotting. It’s highly contagious and previously decimated Arabica crops in Sri Lanka and Indonesia, leading to a shift to Robusta.

Why did Brazilian coffee prices spike in the 1970s?

In 1975–76, a severe frost in Brazil’s Paraná state destroyed 915 million coffee trees. As Brazil produced a third of the world’s coffee, output dropped from 25 million to 8.2 million bags, causing prices to surge from 60 cents to $3.36 per pound.

Does double roasting improve coffee flavor?

Double roasting involves roasting beans twice to fix issues like uneven drying. While it can improve bean appearance, it often leads to a flatter, less vibrant flavor compared to single roasting.

Recommended FrontStreet Beans for Defect Awareness

Explore FrontStreet Coffee’s single-origin offerings to better understand defect-free beans: try the Ethiopia Yirgacheffe for bright floral notes, the Colombia Huila for balanced caramel and citrus, or the Kenya AA for bold blackcurrant acidity. Each showcases what high-quality, defect-screened beans should taste like. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.