Before refrigeration was widely available, canning, drying, pickling, fermentation, and salting foods were common methods of food preservation. Different food preservation methods were used based on the environment and type of food being preserved. People in warmer climates tended to use fermentation, while those in cooler climates could utilise the cold winter weather to freeze-dry different foodstuffs such as meat. Using sugar as a food preservative dates back to Ancient Greece, where it became popular to drench fruits in honey, mash them into a paste, and store it in containers. This was the precursor to the condiment known as jam today.

Jams, jellies, preserves, marmalades, and fruit butters are all the result of boiling fruit, sugar, pectin, and an acid together. The base for any jam is always the fruit component. Pectin is added to the mixture as a way to bind all the components in a gel-like matrix. The acid lowers the pH of the mixture to set the pectin. If the acid does not adequately adjust the pH, the jam will crystallise instead of gelling. Last but not least, sugar is included in the mixture for several reasons. Sugar sweetens the jam, sets the pectin into a well-textured gel, prevents bacterial growth, and enhances the aesthetics of the product.

Legally, a jam or fruit preserve must contain a minimum of 65% soluble solids in the final product to be considered a jam. The majority of these soluble solids present in jam are from sugar, though salts and other dissolved minerals can also contribute. Soluble solids in jam are expressed in units of percent Brix, a measurement based on grams of sucrose/100 grams of mixture. It is important for those producing jam products to hit the minimum amount of Brix in their product as the appropriate sugar content will stave of microbial growth. Sugar decreases water activity in the product by attracting and binding up water molecules. This makes the water unavailable to microbes and thus inhibits harmful organisms from growing in the food.

Application:

A small company that makes marmalades, jams and fruit spreads had been following a family recipe for making their products.  While their product had been popular locally, they were hoping to start distributing regionally. As a result, they wished to better conform to governmental regulations concerning the labelling distinctions between their products. The customer contacted Hanna Instruments looking for a quick and simple way to test the sugar content of their fruit preserves during production as well as on the finished product. This would allow them to adjust the recipes and to classify the final products for sale.