Practical Application of the VST Coffee Refractometer in Retail: From Brewing to Roasting – A Complete Workflow at Justin Coffee

Contents:
1. How Justin Coffee Uses VST to Build Consistent Flavor, Data-Driven Extraction, and Roasting Feedback Mechanisms
2. Why Use VST? How Is It Different from a TDS Water Tester?
3. How Justin Coffee Uses VST in Practice
4. Small Details Matter: Temperature & Cleanliness

How Justin Coffee Uses VST to Build Consistent Flavor, Data-Driven Extraction, and Roasting Feedback Mechanisms

In today’s specialty coffee industry, where "flavor expression" is key, we are placing increasing value on consistency and reproducibility in every cup. At Justin Coffee, maintaining the quality of each cup is not just a matter of craftsmanship — it’s a professional commitment. A key tool that helps us achieve this is the VST Coffee Lab III Refractometer, a precision instrument we’ve integrated into our workflow for measuring coffee concentration.

Why Use VST? How Is It Different from a TDS Water Tester?

Basic TDS water testers (conductivity pens) commonly found on the market are affordable and easy to use, but they measure electrical conductivity, which only reflects the total ion content in a solution. These are suitable for checking mineral levels in water — not in coffee. That’s because coffee contains a wide range of non-ionic solubles like sugars and organic acids, which conductivity pens cannot detect accurately.

In contrast, the VST refractometer uses optical refractive index technology to accurately measure the Total Dissolved Solids (TDS) in coffee. It offers precision up to ±0.01%, making it ideal not just for verifying brew accuracy, but also for correlating extraction yield, roast profiling, and flavor mapping — making it a standard tool for professional quality control.

How Justin Coffee Uses VST in Practice

We’ve incorporated the VST into our in-store three-stage quality control loop: Brewing → Cupping → Roasting. Here’s how we apply it at each stage:

1. Standardizing Brew Strength: Ensuring Consistent Quality in Every Cup
Before any single-origin coffee goes on sale, we run a series of brew tests to identify the optimal TDS range for drinking. For example:
Ethiopia Yirgacheffe, Chebesa Village G1, Natural Anaerobic Washed：At 1.25% TDS, apricot and lemon aromas are bright with a balanced sweetness. At 1.15%, jasmine notes are more prominent, but the sweetness is less pronounced.
We set this TDS range as a brewing reference, along with grind size, water temperature, brew ratio, and pour strategy — ensuring that different baristas can follow the same standard, reducing subjective variation and improving consistency.

2. Cross-Verifying During Cupping: Understanding Flavor Through Data
In addition to tasting and aroma, we also measure TDS during cupping to build a flavor–strength correlation. For example, the same bean roasted to different degrees will yield different TDS results: At 1.15% TDS, the profile may be light and fruity. At 1.35%, fruit notes become more concentrated and sweetness more pronounced. These insights help our internal team understand flavor development and also serve as objective references for roast quality control.

3. Backtracking Roast Profiles: Using Cupping Flavor & TDS to Assess Roast Accuracy
During cupping, we measure TDS to determine whether a roast hits the intended profile. Different roast levels affect solubility: Light roasts tend to have lower TDS, with bright, clean flavors. Light-medium roasts yield moderate TDS, with balanced sweetness. Dark roasts usually have higher TDS and can lean bitter. If the flavor is too heavy and the TDS is high, the roast may have gone too deep. If the flavor is thin and the TDS is low, it may indicate underdevelopment or insufficient heat.

By cross-referencing sensory feedback with measurable data, we can more precisely pinpoint roast outcomes and make micro-adjustments for future batches. This “brewing feedback → roast adjustment” loop is a core part of how Justin Coffee maintains flavor consistency.

Small Details Matter: Temperature & Cleanliness

To ensure accuracy, we recommend letting coffee samples cool to around 25°C before measurement, as high heat can affect refractometer readings. Also, always clean the prism surface with pure water and a clean paper towel after each use to avoid residual interference.

Data brings flavor closer to the ideal. For coffee professionals, sensory training is the foundation — but with the help of scientific tools, our judgment becomes more consistent and convincing. At Justin Coffee, the VST Coffee Lab III plays a vital role in our day-to-day operations, from the brewing station to the cupping table and roasting room. With VST, every pour-over and espresso shot becomes more stable and less reliant on luck. It’s our first step toward data-driven quality management in specialty coffee.

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