The United States’ Food and Drug Administration (FDA) recently banned Red Dye No. 3 and is working to phase out even more dyes in the future. With the added scrutiny, many food and beverage processors have started the process of finding alternatives.  

Natural, plant-based colorants such as beet juice, sweet potatoes and blue carrots are gaining traction. However, for those new to natural dyes, there are important considerations that can impact the final product. How natural pigment is concentrated can affect taste, shelf life and efficiency of use. The latest technological advances in heat technology offer more options than ever before.

Transitioning to Natural Colorant Concentrates 

Natural food colorants are significantly more sensitive to heat degradation and color loss compared to their artificial counterparts, which makes the processing and concentration of these products more critical. 

The food and beverage industry almost exclusively uses natural pigments in a concentrated form. This allows the pigments to be easily transported and incorporated into the end product without having a significant impact on taste, quality or total volume in the recipe. Plant-derived pigments come in a variety of options to suit operators' needs. For example, beet coloring concentrations range from 2% to 70% solutions, with options including liquid or powder.  

The stability of extracted pigments depends on environmental and chemical factors that can occur during processing or storage, such as pH, exposure to light, the presence of metal ions, oxygen and enzymes. However, research shows they are most affected by high temperatures. As a result, evaporators and spray dryers must operate at low temperatures and low residence times to minimize color degradation of the pigment.

Equipment Options 

To concentrate colorants, their solvent — typically water — must be removed, usually by boiling the liquid. For example, manufacturers could take a blue pigment solution at a 5% concentration and remove the water until it reaches a 65% concentration of pigment in the solution. The concentration method can vary depending on the type of evaporator used: falling film plate evaporators, rising film plate evaporators, or other styles of tubular evaporators.  

Evaporators for processing pigments will operate under low vacuum to minimize thermal degradation to the product. They will also typically run in a forward feed configuration (if multiple effects are present) to reduce the temperature the product is exposed to when it is most concentrated.  

Plate evaporators are typically preferred over tubular options thanks to their low installation height and smaller footprint.  

When deciding between plate evaporators like falling film or rising film, time and temperature are vital factors.

Evaporation Considerations 

Residence time, or the amount of time the pigment is subjected to processing, is a critical aspect for the resulting concentration and can vary based on equipment choices. Choosing an option that minimizes holdup time is best, as prolonged exposure to high temperatures can degrade a heat-sensitive product like pigments. For this reason, rising film, forced recirculation and rising falling film evaporators are all poor choices for pigment concentrators.  

Falling film evaporators minimize residence time by distributing evenly across the perimeter of the plate or tube, creating a thin film as it travels down the length of the heat transfer surface. As vapor forms, it accelerates the movement of this liquid film, further reducing its residence time in the evaporator. Falling film plate evaporators still maintain a slight advantage over tubular evaporators in terms of residence time due to their shorter height, creating the same amount of heat transfer surface area by expanding laterally rather than vertically with taller tubes.  

In a falling film evaporator, the feed material is introduced at the top of the plate or tubesheet. Therefore, unlike the rising film design, there is no hydrostatic head to overcome. By eliminating the effect of the hydrostatic head on boiling temperature, it allows falling film evaporators to operate with a very low temperature difference. That means you can run each effect with very low temperature differences, creating a more efficient design with lower steam side temperatures. The result is less thermal degradation.

Concentration Impacts 

Evaporation methods have a significant effect on pigment concentrations and their end product. Impacts on product quality from concentration methods can include:

• Taste: If the pigments are subjected to high temperatures or cooked for too long, it can result in a stringent flavor.
• Shelf life: Light and heat exposure can break down a product and cause it to spoil faster. The length of time colorants are processed will affect their ability to preserve color intensity during extended shelf life. Quicker processing will keep the color brighter for longer.
• Uniformity and consistency: Inconsistent concentration quality can cause discrepancies in end product color.  
• Efficiency: Concentration amounts must remain stable to ensure ratio amounts are consistent within a recipe. Additionally, if more pigment is required, costs can increase.  

The downstream impacts of concentration methods can affect both consumer satisfaction and a business’s bottom line. Understanding the differences in evaporation methods is crucial for transitioning to food coloring made with natural ingredients.