In instant-coffee production, aroma can be lost at many points before the final powder is packaged. If only the final powder is analyzed, you can't know whether a compound was lost at extraction, concentration, or drying. The concept of aroma recovery is therefore broader than the drying step's own volatile-retention ability: it asks what portion of the original aroma compounds was retained throughout the whole line.

Aroma can be lost at many streams of the line

Right at the extraction step, not every aroma compound follows the same stream. Some volatile substances can escape the aqueous phase, while less-volatile substances are better retained. Thermal conditions, pressure, and time can change this distribution. Research on pressure-cycling extraction shows different operating configurations affect not only efficiency

Concentration is a sensitive point because water is removed from the liquid and heat is transferred into a stream with increasing solids concentration. As concentration rises, mass-transfer coefficient and viscosity change. If the process creates vapor containing aroma compounds, part of the aroma can be carried along. Industrially, recovering aroma fractions from the vapor stream can be used as a

Recovery needs to be built from mass balance and sampling points

If you only look at the final powder, you know aroma was lost but struggle to know where. Tracking each intermediate stream turns the sensory question into a checkable mass-balance problem.

To calculate recovery, you need a mass-balance basis. You can quantify the target compound in the raw material or initial extract, then measure at intermediate streams and the final product. You don't need to quantify every compound; a marker group can be chosen based on sensory significance and analytical stability. What matters is using the same method and calculation basis

One difficulty is that aroma-compound content is very low and the coffee matrix is complex. GC-MS, GC-olfactometry, or related techniques can be used for identification and quantification, but sample recovery, standards, and repeatability need to be controlled. Otherwise, the difference between two steps could just reflect analytical error.

Aroma recovery also doesn't equal sensory quality. A product with high total volatile-compound amount can still have an unbalanced odor profile. Conversely, some compounds may decrease while high-sensory-value compounds are well retained, potentially creating a better perception. So target-compound selection should be based on odor threshold and role in the aroma profile

High recovery doesn't necessarily create a good aroma profile

Line data should be organized by material stream and aroma stream. For each point, record stream mass, solids, temperature, pressure, and target-compound concentration. When these datasets are linked, you can identify which step causes the largest loss and assess the effect of an operating change.

Recovery of aroma compounds is therefore a traceback problem. It shifts the question from “is the final powder still aromatic?” to “where did the aroma go throughout the whole line?” This view is more useful for process improvement since it lets you find the right point for intervention, while avoiding confusing the concentration effect with genuine aroma recovery.

Tracking the flow network to trace the source of aroma loss

At the technology level, aroma recovery can be viewed as a flow network. Compounds enter from the raw material, are released during extraction, distribute between liquid and gas phase, then continue through concentration and drying. Each step creates its own recovery coefficient. Multiplying these coefficients shows why a small loss repeated across many steps can create a large difference in the final

Vapor and condensate streams can also carry important information. If some marker compounds in these streams are analyzed, you can identify which step is actually the source of aroma loss. This is a more practical approach than simply increasing added aroma at the end of the line without knowing where the loss occurs.

Aroma recovery also needs to assess the stability of the recovered aroma fraction. An aroma-rich fraction that's prone to change during storage doesn't necessarily create a corresponding benefit. So recovery should go together with checking composition, stability, and the ability to reintroduce it into the product stream.

Choosing marker compounds and assessing the stability of the recovered aroma fraction

When designing a study, you don't need to quantify the entire aroma system. You can choose marker compounds representing important odor groups, as long as the reason for selection is clearly stated. This approach reduces analytical complexity while still allowing traceback of meaningful changes.

Some notes when reading the data

When calculating recovery, you need to check whether the total compound amount measured across streams is reasonable relative to the amount fed in. If the discrepancy is too large, the cause could lie in an unsampled stream, loss during sampling, or analytical error. Checking this balance helps avoid attributing the entire shortfall to one technology step.

References

• Fryer et al. (2020), Modeling Mass and Heat Transfer in Multiphase Coffee Aroma Extraction, Industrial & Engineering Chemistry Research, 59, 11099–11112. DOI: 10.1021/acs.iecr.0c01153.
• Mathematical modelling of the steam stripping of aroma from roast and ground coffee (2019), Energy Procedia, 161, 157–164.
• Volatile Aroma Recovery from Roasted Coffee by Steaming and its Effects on Soluble Coffee Products (1992), Journal of the Japanese Society for Food Science and Technology.
• Concentration of aroma compounds from an industrial solution of soluble coffee by pervaporation process (2015), Journal of Food Engineering, 159, 57–65.