SOP: Determination of Total Solids by Vacuum Oven Drying

GIFSQ — Global Institute for Food Safety & Quality

Principle

The total solids content is the residue left after the complete removal of water from the sample. Drying under vacuum at 70 °C drives off the moisture without caramelizing the sugars or decomposing heat-sensitive constituents of the juice.

Apparatus required

• Vacuum oven (capable of holding 70 °C)
• Flat-bottomed drying dishes with tight-fitting lids
• Desiccator
• Analytical balance

Procedure

Weigh a known quantity of the well-mixed sample into a tared drying dish

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Dry in the vacuum oven at 70 °C until a constant weight is reached

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Cool in a desiccator and weigh the dried residue

Calculation

Total solids, % (w/w) = (Weight of dried residue / Weight of sample taken) × 100

Precautions

• Mix the sample thoroughly before weighing so the portion taken is representative.
• Do not exceed 70 °C; higher temperatures can caramelize sugars and falsify the result.
• The book’s determination is a single line (“Determine by drying in a vacuum oven at 70 °C”); the apparatus list and calculation above are the standard laboratory setup.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.