Inexpensive hand held refractometers are a convenient means of determining the end point of jam making.
Fig 1 shows a hand held refractometer suited to jam making. It has a range of 58°Bx to 90°Bx, with Automatic Temperature Compensation and calibration thumbscrew.
Refractometers can be calibrated using a known calibration liquid. Calibration oils with refractive index equivalent to around 70°Bx are expensive and difficult to obtain.
Virgin olive oil is specified by the UN FAO in CODEX STANDARD FOR OLIVE OILS AND OLIVE POMACE OILS CODEX STAN 33-1981 (Rev. 2-2003) to have a refractive index from 1.4677 to 1.4705 at 20°C which corresponds to 71°Bx to 72°Bx.
Whilst virgin olive oil is not as accurate as calibration oils, it is quite adequate as a calibration standard for the purpose of jam making, and should indicate between 71°Bx to 72°Bx.
Recipe FAQLast modified 19 November 2014 20:09.
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