The fundamental rheological property that sets a gummy apart from a caramel or a fruit chew is its elasticity relative to its viscosity: the balance between the storage modulus (G′) and the loss modulus (G″). This balance is expressed as the phase angle (δ), or as the ratio tan δ = G″/G′.
Gummies are designed to be elastic gels. Stretch one and it snaps back. The structure is a cross-linked polymer network, gelatin or pectin, that stores energy and resists flow. Under small deformations G′ runs far above G″, so the phase angle δ sits well below 45°. A caramel is a concentrated sugar-glass matrix with fat and milk proteins. It flows under stress instead of recovering: G″ exceeds G′, and δ moves toward 90°. Fruit chews sit between the two, softer and less elastic than a gummy but more solid-like than a caramel, with the rheology tuned to balance chewiness and release.
Measuring that distinction inline
Tan δ is read on a rheometer in the QC lab rather than a sensor in the pipe. A sample of the cooked mass, or a finished piece, is loaded between parallel plates or a cone and plate, and the instrument applies a small oscillation at a controlled frequency and strain. The steps are:
- Small-Amplitude Oscillatory Shear (SAOS): The probe oscillates while the sample stays still, at a strain small enough not to break the gel network.
- Signal decomposition: The instrument calculates G′ (storage modulus) and G″ (loss modulus) from the phase shift between the applied strain and the measured stress.
- Tan δ calculation: δ = arctan(G″/G′) collapses the two moduli into one number. A tan δ far below 1 marks a firm, gummy-like gel; a tan δ above 1 marks a viscous, caramel-like body.
Plants do not get a live G′ and G″ readout on the line. Inline sensors track the variables that set those moduli: a sanitary refractometer reads Brix, or solids concentration, through the cooking step, a process viscometer reads viscosity, and thermocouples track temperature. At a manufacturer like KorNutra, operators adjust cooking time, gelling-agent dose, and cooling rate against those inline signals, and the lab rheometer confirms the result.
Temperature and frequency shift tan δ
A rheometer reports tan δ under one set of conditions, and the number moves when the conditions change. Gels soften and turn more liquid-like as temperature rises; caramel is a clear case, reading more viscous at higher temperature. Frequency matters the same way. A slow oscillation gives the network time to relax, so the material looks more solid, while a fast one reads stiffer, and past a point G′ and G″ cross. A usable texture spec names frequency, temperature, and strain alongside the tan δ target. Holding temperature and solids inline keeps the material on the right part of that curve.
Texture has to stay steady from batch to batch, so operators watch the inline Brix, viscosity, and temperature and adjust before the lab rheometer reports. A drift in those inline readings gets corrected during the run, so the finished piece keeps the snap that separates a gummy from a softer chew or a flowing caramel.