Simply put, cooking under vacuum reduces the boiling point of the mass being cooked. The higher the vacuum applied, the lower the temperature required to drive off moisture.
Why is this important? There are several reasons, but the primary one is to minimize degradation of ingredients processed at high temperatures.
The atmospheric boiling point of a water/sucrose solution varies depending on the % solids. A 75% sugar solids solution begins boiling at about 225° F, whether it’s sucrose or sucrose and corn syrup. As water evaporates off, the solids increase and the boiling point also increases. The ideal % solids for a typical hard candy is 97 – 98%. This occurs at about 300° F, which is also the temperature where sucrose begins to decompose or “caramelize.”
The classic example of the above is stove-top cooked hard candy. Cooking a hard candy formula atmospherically to 300° – 305° F on an electric range will typically result in a darkened base with a “scorched” or “burnt” flavor note. However, by cooking under vacuum to a final cook temperature of 240° – 285° F, the same residual moisture can be achieved with no discoloration, and the mass will have a clean flavor profile.
If your new product challenge involves controlling moisture, delivering a clean flavor profile, and retaining functional attributes of key ingredients, vacuum cooking may be the solution.