How to use the LINK Density Tube

The LINK sample roaster is a cutting-edge tool designed to simplify and refine the roasting process for coffee professionals and enthusiasts alike. Developed by Nucleus Coffee Tools, the LINK roaster combines advanced technology with user-friendly design to deliver precision roasting for coffee samples between 50 and 100 grams. A key feature of the LINK system is its use of green coffee density measurements, which form the foundation for its highly accurate roasting profiles.

Density plays a vital role in coffee roasting because it directly affects how beans absorb and respond to heat. Denser beans tend to roast more slowly due to their compact structure, while less dense beans roast faster and require a gentler heat application. To make density measurements more accessible, Nucleus Coffee Tools included the density tube with every LINK roaster. This tool allows users to take consistent, reliable density readings of green coffee, which can be input into the LINK App to generate precise roast profiles tailored to the coffee’s characteristics.

In this article, we’ll cover what the density tube is, why density measurement is critical to the LINK roaster’s functionality, and how to differentiate between the two types of density tubes available.

What is a 'Density Tube', and how does it work?

The density tube is a compact, calibrated container that enables users to measure the “volume by weight” density of green coffee beans. By capturing this data, the LINK roaster can recommend roast profiles that align with the specific density of the coffee being roasted.

Using the density tube is straightforward. First, fill the tube with green coffee beans, ensuring the beans are level with the top of the container. Avoid compressing the beans, as this can affect the accuracy of the measurement. Once the tube is filled, weigh it on a scale to determine the density value. This weight is entered into the LINK App, which calculates a roasting profile designed to optimise heat application and development time for your coffee.

The density tube’s precise measurements are especially useful for coffee professionals working with diverse origins and processing methods, as it accounts for subtle differences in bean structure and composition.

Why the LINK uses density measurements

Density is a critical variable in coffee roasting because it influences how heat transfers through the beans. Beans with higher density, often grown at higher altitudes, contain tightly packed cellular structures that require more energy to reach optimal development. Conversely, beans with lower density roast more quickly due to their looser structure.

Nucleus Coffee Tools selected density as a core metric for the LINK roaster because it provides a reliable and measurable way to adapt roasting profiles to different coffees. While factors such as processing method and variety also impact roasting behaviour, density offers a direct link to the coffee’s physical properties.

The LINK App integrates density readings seamlessly into its workflow. After measuring the density with the tube, users can input the value into the app alongside details about the coffee’s processing method and variety. The app’s algorithm then suggests a roasting profile tailored to the coffee, ensuring optimal flavour development and consistency.

This approach not only simplifies the roasting process for beginners but also enhances precision for seasoned professionals, allowing them to replicate results across batches.

Different Density Tubes and how to differentiate between them

During the production of the LINK density tubes, two distinct versions were created: Type 1 (formerly V1) and Type 2 (formerly V2). Neither is newer, or better – they’re simply two different versions of the same thing.

Additionally, the LINK App allows users to select their tube version in the “Preferences” tab. This ensures the profiling algorithm adjusts for any differences in tube design, providing accurate recommendations regardless of the version.

While both versions function effectively with the LINK roaster, they differ slightly in weight and texture, which can influence the app’s profiling recommendations. Here’s how to identify which density tube you have:

Type Density Tube

• Weight with lid: 57–65g
• Weight without lid: Above 36g
• Texture: Polished and smooth to the touch
• Base shape: Slightly rounded, slightly thicker walls

Type 2 Density Tube

• Weight with lid: 51–57.8g
• Weight without lid: Below 32-37g
• Texture: Slightly textured to the touch, grainy
• Base shape: Squarer, slightly thinner walls

If you’re unsure which tube you have, you can also perform a water test. Fill the tube (without the lid) with water until a meniscus forms at the top, then weigh it. The water weight will confirm whether you’re using a Type 1 or Type 2 tube:

Type 1 water-filled weight: Below 98-99g

Type 2 water-filled weight: 98–101g

If your tube has inconsistent data (eg. the weight with lid indicates Type 1, but the texture indicates Type 2, the Base Shape is the best indicator for your Tube type. For more information on this, see the video below.

How to set up the LINK Density Tube for roasting

To get started with your density tube, follow these steps:

1. Prepare Your Green Coffee: Weigh out 80–100g of green coffee beans and ensure they are free of defects or impurities.
2. Calibrate Your Scale: Tare your scale with the empty density tube to ensure an accurate reading.
3. Fill the Density Tube: Add your coffee beans gently, ensuring the tube is slightly overfilled. Avoid compressing the beans.
4. Level the Beans: Use the inverted lid to scrape off excess beans, ensuring a flat surface at the top of the tube.
5. Weigh the Filled Tube: Place the filled tube on the scale and record the weight. This is your coffee’s density measurement.

Enter this measurement into the LINK App under the “Profile Selector” tab. Along with other inputs, such as processing method and variety, the app will generate a roast profile optimised for your coffee.

The density tube is more than just an accessory for the LINK roaster—it’s a gateway to precision and consistency in coffee roasting. By incorporating density measurements into the roasting process, Nucleus Coffee Tools empowers users to unlock the full potential of their green coffee. Whether you’re working with high-altitude Ethiopian beans or naturally processed Brazilians, the LINK system ensures that every roast is tailored to the coffee’s unique characteristics.

For further guidance on using the LINK roaster and density tube, browse the Nucleus Coffee Tools website, consult the user manual, or chat with our Virtual Roast Assistant, Marv on our website or the LINK App.