It is preferable to use glass jars with new metal lids. Paper, polythene or cloth lids can also be used, but they look less professional and there is more risk of spoilage. Plastic containers with foil lids can also be used if available as these tend to be cheaper than glass.
All equipment must be thoroughly cleaned each day to prevent contamination by insects and micro-organisms.
Preparation of 5 SAG pectin working solution:
- 30g of 150 SAG pectin
- 150g sugar
- 720ml water
- Mix the pectin and sugar thoroughly.
- Heat the water to 70-75°C and slowly add the sugar/pectin, mix with constant stirring.
- If a small electric stirrer is available there will be less chance of lumps forming.
- Heat to boiling and boil for 1 minute, again with constant stirring.
- Hold at 50-60°C (a double saucepan is useful here).
Sugar has two main roles: to set the preserve and to prevent microbial spoilage. The final concentration has to be high enough (>68%) to prevent fermentation by moulds or yeasts, but low enough (<72%) to prevent crystallization.
Refined, granular, white sugar should be used, but even this will often contain small amounts of material (black specks) which reduce the value of a preserve. The sugar should be dissolved in water to make a strong syrup and then filtered through muslin cloth or a fine mesh.
The fruit must have a high level of acidity (pH 3.0-3.3) to enable the pectin to form a gel. This is not a problem with most fruits but melon, papaya and banana are all low-acid fruits that need citrus juice or citric acid to be added.
Citric acid, malic acid or tartaric acid are added to adjust the pH of the fruit pulp to 3.0-3.3. Citric acid is usually used as this one is most widely available.
Calculation of Yield
Total yield = Total soluble solids (TSS) of raw materials / Percentage of total soluble solids in final product x 100
Determination of Total Soluble Solids
The soluble solids content of a solution is determined by the index of refraction. This is measured using a refractometer, and is referred to as the degrees Brix. It is widely used during fruit and vegetable processing to determine the concentration of sugar in the products.
Sugar concentration is expressed in degrees Brix. At 20°C, the Brix is equivalent to the percentage of sucrose (sugar) in the solution (60° Brix is equivalent to a sugar content of 60%). The measurement must be made at 20°C to get an accurate value.
Measurement of Degrees Brix
- Ensure the solution is at a temperature of 20°C.
- Place one or two drops of sample onto the prism and close the prism carefully. The sample should be evenly spread over the surface of the prism.
- Hold the refractometer near a source of light and look though the field of vision.
- The line between the dark and light fields will be seen in the field of vision. Read the corresponding number on the scale. This is the percentage of sugar in the sample.
- Open the prism and remove the sample with a piece of paper or clean wet cotton.
For more information, contact:
BLTD Technology Resource Center
2nd Flr. Jacinta 2 Bldg., EDSA, Guadalupe Nuevo, Makati City
Email: [email protected]
Telephone: (02) 822-5087;
Truckline: (632) 822-54-18 loc. 207, 204 & 201