Caramel Batch Grains After Scale-Up

The endpoint temperature was copied, but the heat and mass transfer were not. A 600 L batch has a much smaller surface-to-volume ratio than a 20 kg open pan, and a jacketed scraped kettle removes water mainly at the surface and through the jacket. The batch took 55 minutes instead of 15, so the same 118°C endpoint did not deliver the same solids: 11.5% moisture versus 8–9% means the caramel is under-evaporated. Residual water softens the matrix and, at warm storage or wrapping tension, produces stickiness and cold flow.

Graining is a separate crystallisation problem. Sucrose can crystallise if crystals are present as seeds or if the sucrose is not fully dissolved before boiling. Fine granulated sugar added to a large batch can remain undissolved at the bottom or on the kettle wall; scraped surfaces can also leave dried sugar crystals that seed the mass. The long cook then concentrates the syrup around those crystals. Glucose syrup normally inhibits sucrose crystallisation, but it cannot compensate for undissolved seed crystals or a badly balanced sugar solids ratio. The higher moisture also keeps the mass fluid longer, allowing crystals to grow before the caramel sets.

First fix dissolution: charge water, glucose syrup, and sucrose together, heat with agitation to a clear solution before adding milk and butter, and filter or strain if necessary. Do not dust dry sugar into a hot concentrated mass. Rebalance the recipe so glucose syrup solids are a deliberate proportion of total sugar solids, not simply scaled; confirm the 42 DE syrup specification and adjust if a different DE is supplied. Because the kettle evaporates more slowly, cook to a target solids rather than only to 118°C: use a refractometer or moisture check and expect a higher endpoint temperature, or use vacuum to hit 8–9% moisture without excessive heat exposure.

In-process checks: verify full dissolution before boiling; record batch depth, steam pressure, agitation, and cook time; check boiling point or refractometer readings at intervals; measure final moisture on a cooled sample; and record the cooling regime. Rapid cooling after the endpoint helps set the texture and limits crystal growth. Hold the first production batch for a 10-day texture check before releasing the full order. If graining persists, examine the glucose syrup DE and dose, and check for crystal seeds from utensils, scrapers, or recycled trim.

Use a controlled trial rather than assuming. Retain samples of the newly opened glucose syrup and the sucrose, and run small pilot batches with the original 20 kg method: one with the current glucose syrup, one with a known-good syrup, one with the current sucrose, and one with a known-good sucrose. Keep the cook endpoint and cooling identical, then evaluate graining at 10 days and measure moisture. If the current sucrose grains in the pilot, check for undissolved crystals, particle size, and storage conditions. If the current glucose syrup grains only in the pilot, check DE, dry substance, pH, and whether the drum was diluted or contaminated.

Also inspect the 600 L kettle: scraper condition, dead zones, temperature distribution, and whether dried caramel or sugar crust from a previous batch was left on the wall. Review the batch record for charge order and agitation during dissolution. If the pilot batches are smooth but the production batch grains, the fault lies in the kettle process, not the ingredients. Document the trial in the corrective-action record and update the scale-up procedure with a dissolution step, solids endpoint, and verification check.