Food & Brewing Density Meter Selection Guide

Steps

1. Brewing (bubbles and dark colour)

   Wort and beer combine dissolved extract with dissolved CO2 and, in places, active fermentation. Recommended: PS7110 refractometer, because the critical-angle method reads only the thin layer at the prism face and is therefore unaffected by dark colour, turbidity or bubbles — the exact combination that defeats most other optical approaches. This is the property that makes it the default for brewing. Note that in fermenting wort, alcohol and extract both change refractive index, so a single refractive reading gives apparent rather than true extract; where both are needed, that requires either a second independent measurement or a spectral method. State which you need at enquiry.

2. Spirits and rice wine (alcohol plus sugar)

   A two-component problem in disguise. Alcohol lowers density while sugar raises it, so a density reading alone cannot resolve both, and two liquids of very different composition can share a density. If the process holds sugar effectively constant, the system reduces to binary and a sound-speed instrument such as the PS7020 gives fine resolution on alcohol content. If both vary independently, use a spectral method (PS7100) or accept that an independent input is required. This is worth settling before purchase — it is a physical constraint, not a calibration exercise.

3. Sugar refining (high Brix with crystals)

   High-Brix syrup with suspended crystals in massecuite service. Recommended: PS7110, which resolves 0.02 Brix and is specified at ±0.15 Brix, with direct traceability to a laboratory refractometer so plant and lab agree on the number rather than arguing about it. The important caveat: a refractometer reads dissolved solids at the prism face, so in massecuite it reports mother-liquor purity rather than total solids including crystal. That is often exactly what the crystalliser control needs — but it must be the intent, not a surprise. Fouling of the prism shows as slow drift, so specify a self-cleaning position or a wash provision.

4. Condiments (soy sauce, vinegar, fish sauce)

   Dark, high-salt, sometimes with suspended solids, and often produced in batch. Recommended: PS7110 for the same reason as brewing — colour does not blind it. Salt and dissolved organics both affect refractive index, so calibrate on the actual product rather than on a generic curve, and recalibrate when a recipe changes. High chloride also constrains materials: confirm wetted parts against the salt concentration at process temperature, since a stainless steel that is fine on vinegar may pit on high-salt fish sauce.

5. Beverages and juice (with pulp)

   Juice with suspended pulp is the case where reading a thin layer at a window can differ from the bulk, since pulp content varies and may not be represented at the prism face. Recommended: PS7110 where the specification is dissolved-solids Brix — which is usually what the product standard is written against — and be explicit in the specification that this is dissolved solids, not total solids. If total solids including pulp must be controlled, that is a different measurement and needs a different principle. Also confirm behaviour through the deaeration step, since dissolved gas is managed differently upstream and downstream of it.

6. Dairy (strict CIP / SIP)

   Dairy is where the cleaning regime, not the measurement, tends to decide the instrument. Milk and cream are emulsions of fat globules, so fat content and total solids both matter and they influence density differently. Specify against the CIP/SIP cycle first: peak temperature, chemical concentrations and cycle frequency, plus any SIP steam condition. Then confirm that the process connection drains completely in the installed orientation — a fitting that holds a few millilitres of product is a hygiene finding regardless of how well it measures. Confirm food-contact documentation for every wetted material including seals, not just the main body.

7. Edible oils and custody transfer

   Vegetable and edible oil transfer is a commercial measurement, so the requirement moves from process control to metrology: what matters is the traceability of the calibration and the stability of the reading over months, not a single accuracy figure. A Coriolis instrument such as the PS7200 gives density and mass flow from one sensor, which removes the reconciliation between two instruments with two calibration histories. Two cautions: oils are viscous, so pressure drop through bent tubes is a real hydraulic cost worth checking against the pump, and entrained air from tank filling will corrupt a Coriolis reading badly — mount so that gas cannot collect and confirm the line runs full. If the transfer is contractual, establish which metrology approval the counterparty requires before selecting, because that requirement can eliminate otherwise suitable instruments.