AA GRADE COFFEE

 

The AA Grade: Why Screen Size 18 Matters for Your Perfect Coffee Roast

 

The world of specialty coffee is rich with terminology, but few labels carry the weight and the price tag of AA Grade coffee. Often associated with premium, high-altitude crops from celebrated origins like Kenya and Papua New Guinea, the "AA" label is often misunderstood. It doesn't strictly guarantee a superior flavour; rather, it is a precise measure of physical bean size. Specifically, it denotes a bean that is large enough to be retained by a screen size 18 sieve (approximately 7.2 mm).

Yet, this simple physical grading is intrinsically linked to the complex, desirable flavours roasters and consumers crave. This in-depth guide explains the vital role of this screen size, explores the most famous AA origins, and provides the expert roasting tips you need to unlock the maximum potential of these impressive large beans.

The Science of Bean Sorting: Consistency is King

For any professional or home coffee roaster in the Australian coffee scene, uniformity is the foundation of quality. Whether you're producing a large batch for a busy café or a small lot in your garage, every bean needs to roast at the same rate. This is precisely the function of the coffee grading system.

Grading is a mechanical process that occurs at the dry mill after the coffee cherries have been processed and dried. Green beans are passed through a series of woven metal screens with circular holes of specific diameters. To earn the AA classification, a bean must be retained by a screen size 18 (an opening of 18 / 64 of an inch, or 7.14 mm).

This sorting is essential for quality control because uniform size ensures even heat transfer during roasting. If your batch contains a mix of small and large beans, the small ones will over-roast, leading to burnt or smoky flavours, while the large ones will remain under-developed or 'baked' in the centre. Buying AA grade coffee is therefore a primary guarantee that you are working with large, consistently sized beans.

Need a dependable roasting foundation? Explore our selection of Green Coffee Beans that are meticulously graded for superior roasting consistency.

Why Bigger Beans Often Taste Better: Size, Density, and Altitude

The notion that a bigger bean automatically means better coffee is an oversimplification. A massive bean grown quickly at a low altitude may taste flat and earthy. However, the strong correlation between AA size and premium flavour is rooted in the physics of coffee cultivation: high altitude.

Coffee cherries grown at higher elevations (often above 1,500m) mature much slower than those at lower elevations. This slow development is crucial, as it allows the bean to absorb significantly more sugars, complex acids, and nutrients from the coffee plant. The result is often a physically larger bean, and more importantly, a bean with higher cellular density.

Density is the secret to unlocking complexity. Dense beans can endure a higher application of heat without scorching and hold more volatile, flavour-carrying compounds. Since AA beans are the largest of the crop, they frequently overlap with the densest beans from the most desirable, high-altitude microclimates. This is why a premium AA lot is so often synonymous with a superior cup profile, suggesting the bean had the ideal time and conditions to fully develop.

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The World's Most Famous AA Origins

While many countries sort their coffee by size, two origins are universally revered for the quality and reputation of their AA classification:

Kenya AA: The Benchmark for Complexity

Kenya AA is arguably the most famous grading term in the specialty coffee industry. The Kenyan coffee system, particularly its government-run auction process, rewards both quality and size, creating strong incentives for producers to achieve the AA standard.

Kenyan coffee is celebrated for its intense, vibrant flavour profile, often described as having a sparkling, bright acidity. Typical flavour notes include:

• Blackcurrant and Grapefruit

• Tomato and Wine-like complexity

• Potent, syrupy body

The AA designation here promises a bold, evenly cooking bean that is ready to release these potent aromatics, making it a jewel for roasters offering a high-end Single Origin Coffee.

Papua New Guinea (PNG) AA: Smoothness Closer to Home

Closer to Australia, Papua New Guinea AA coffee has long been a staple for both blends and single-origin menus. PNG's growing environment, with incredibly fertile volcanic volcanic soil and high-altitude smallholder farms produces exceptional beans.

While the PNG grading system has recently been modernised (with 'AA' now often denoted as '18+'), the tradition of classifying large, clean beans as AA remains. Unlike the sharp acidity of Kenyan beans, PNG AA often delivers a softer, smoother cup:

• Buttery, silky body

• Notes of Milk Chocolate and Tropical Fruit

• Clean, balanced, and sometimes herbal finish

Because of our proximity, Coffee Hero often sources some of the freshest screen size 18 coffee from this region. You can often find a spectacular PNG AA in our premium PNG X - Single Origin Medium Dark Roast Coffee Beans offering.

AA vs. AB and Peaberry: Understanding the Grades

When you see a price difference on a coffee menu, it helps to know what you’re comparing. The AA grade is part of a larger, country-specific system of classification.

The difference between AA vs AB coffee beans is simply size. Both can come from the same tree and taste equally good, but AA is rarer, visually more appealing, and commands a premium.

Peaberry is a natural mutation where the coffee cherry develops only one rounded seed instead of two flat-sided ones. Though smaller than AA beans, their round shape and incredible density make them roast differently, often resulting in a concentrated, vibrant cup profile.

Expert Roasting Tips for AA Grade Coffee

Roasting AA grade coffee is a joy because the uniformity allows you to focus purely on development. However, their size and density demand a calculated approach to heat management.

Because AA beans are large and dense, heat requires more time and energy to penetrate to the core. A gentle approach risks "baking" the coffee and flattening the flavour profile. A too-hot, too-fast approach can scorch the exterior while leaving the inside raw.

Here is a streamlined profile strategy for getting the most out of your screen size 18 beans:

1. High Charge Temperature: AA beans have a lot of mass. Start with a slightly higher initial (charge) temperature than you would for smaller beans to ensure a powerful thermal push gets energy into the core.

2. Monitor the Turning Point (TP): The temperature dip when the beans are added (TP) needs to be managed carefully. If it's too sluggish, increase your gas/heat application to prevent a slow, baked roast start.

3. Extended Maillard Reaction: The Maillard phase (where beans turn yellow/brown) should be slightly extended for large, dense beans. This extra time allows for flavour development and Body-building without losing the desirable acidity.

4. Anticipate First Crack: Large beans release a massive amount of moisture during the first crack, which can rapidly cool the drum and stall the roast (crashing). Be ready to increase your airflow and/or gas to power through the crack.

5. Check Development: After the roast, break a bean open. The colour must be uniform from the outside to the centre a visual sign of a perfectly developed, evenly cooked AA bean.

Ready to master your own roast? Learn more about the factors that influence bean quality in our detailed guide: HOW TO FIND HIGH-QUALITY COFFEE BEANS.

Take the Next Step in Your Coffee Journey

AA grade coffee is a testament to the pursuit of excellence and consistency in the world of specialty coffee. By understanding that the screen size is a powerful indicator of potential quality, and by applying the right roasting techniques, you can reliably unlock the complex, vibrant flavours these beans are famous for.

Strengthen Your Expertise with Credible Sources

To solidify your understanding of the global coffee supply chain and the nuances of high-quality classification, we recommend exploring these authoritative resources:

• Specialty Coffee Association (SCA) Grading: For official standards on quality, cupping, and the 100-point scoring system that complements size grading, visit the SCA Resources page 

• International Coffee Organization (ICO) Quality Standards: To understand how bean density, defects, and grading systems are used globally by regulatory bodies, explore the ICO Market Development Resources 

Ready to Taste the AA Difference?

1. For Home Enthusiasts: Stop settling for inconsistent roasts. Shop our latest Single Origin AA offerings today and taste the uniform quality of screen size 18 for yourself!

2. For Commercial Roasters: Demand the best for your customers. Contact us for wholesale pricing on bulk green AA lots and elevate your entire menu.

3. Level Up Your Knowledge: Want to truly understand flavour? Read our complete guide to What Is Single Origin Coffee?, which is often where the highest grade AA beans are found.