Selecting and Preparing Colorants for Endoscopic Swallowing Assessments


Based off the research described below, I recommend using two types of liquid boluses during a standardized FEES protocol: (1) heavily-concentrated white-dyed water; and (2) blue or green, opaque water. As described below, the types of contrasts used during FEES can significantly influence the detection of functional swallowing impairment (pharyngeal residue, penetration, and aspiration). Therefore, it is important to standardize what types of contrasts are used during FEES and SEES to ensure the validity and reliability of the endoscopic swallowing assessment. Three contrast properties that have been previously researched as they relate to detecting pharyngeal residue, penetration, and aspiration during FEES include 'color', 'coating', and 'opacity.'


The effect of color has been studied the most as it relates to detecting of functional swallowing impairments during FEES. Three studies examined the reliability of rating functional impairments as an effect of food dye. Research comparing blue-dyed milk to naturally white (non-dyed) milk found inter-rater reliability to be descriptively higher for the naturally white milk for ratings of pharyngeal residue, penetration, and aspiration (Leder et al., 2005). Research comparing green-dyed milk to naturally white (non-dyed) milk found rater reliability to be greater for the green-dyed milk for ratings of penetration/aspiration (Marvin et al., 2016). Lastly, research comparing reliability of barium water, blue-dyed water, and green-dyed water found reliability to be highest for green-dyed water and barium, and lowest for the blue-dyed water (Curtis et al., 2019).

Three studies have examined the sensitivity of rating functional swallowing impairments during FEES as an effect of color. In a study comparing green-dyed milk to naturally white (non-dyed) milk, more severe penetration-aspiration was observed more frequently for the green-dyed milk compared to the naturally white milk (Marvin et al., 2016). In a study comparing green- and blue-dyed water, no differences in detection rates were observed between blue- and green-dyed water (Curtis et al., 2019). In a study comparing blue-dyed milk to naturally white (non-dyed) milk, pharyngeal residue and penetration-aspiration were seen more frequently with blue-dyed milk compared to naturally white milk (Curtis et al., 2021).

Together, these data suggest that, from a color standpoint, green may the most reliable and sensitive color for assessing functional swallowing impairments during FEES, followed by white and blue respectively - though the differences between colors (i.e., their effect size) appear relatively small.


The effects of coating has been directly researched in one study (Curtis et al., 2021) and indirectly researched in a second study (Curtis et al., 2019). In both studies, liquids containing a coating effect (heavily concentrated white-dyed water, barium water) were seen substantially more frequently compared to other liquids. Coating appears to have a very large effect on the detection of pharyngeal residue, penetration, and aspiration during FEES, compared to the relatively small effects of color and opacity. Therefore, data suggest that coating is the most important contrast property for assessing functional swallowing impairments during FEES. Because of this, it is important to ensure that each swallow condition examined during FEES includes at least one trial using a contrast that possesses a coating effect.

So, what types of liquids contain a coating effect? Our 2021 study compared heavily concentrated white-dyed water, barium water, naturally white milk, blue-dyed milk, and blue translucent water to identify which types of liquid boluses exhibited a coating effect most frequently. This study found heavily concentrated white-dyed water exhibited a perceived coating effect for ~96.7% of thin liquid swallows, compared to 80% of barium water swallows, 13.3% of blue water swallows, 6.7% of white milk swallows, and 0% of blue milk swallows.


The effect of opacity on the detection of pharyngeal residue, penetration, and aspiration has been directly studied in one study whereby blue-dyed milk (opaque) was compared to blue-dyed water (translucent/non-opaque) (Curtis et al., 2021). The effects of opacity have indirectly research in several other studies whereby dyed-waters were compared to dyed milk or barium but where opacity wasn't a central research question (e.g., Curtis et al., 2019; Butler et al., 2018). Together, these studies found small effects of opacity on the detection of functional swallowing impairments, with pharyngeal residue, penetration, and aspiration observed more frequently for liquids that were opaque compared to non-opaque.


Coating is the most important contrast property for detecting pharyngeal residue, penetration, and aspiration during FEES. It is reliable and sensitive and demonstrates a large effect size. Color and opacity also influence the detection of functional swallowing impairments, albeit to a lesser extent than coating.


A standardized FEES protocol should include multiples trials for each swallowing conditions. Given the above research, I recommend having one trial within each liquid swallowing condition be heavily-concentrated white dyed water and another trial within each liquid swallowing condition be a colored-opaque liquid with minimal-to-no coating effect.

Having one trial within each swallowing condition be a heavily concentrated white-dyed water will maximize sensitivity and reliability of detecting pharyngeal residue, penetration, and aspiration. However, one problem with coating effect liquids is that over time the dye/barium can coat ("gunk") the camera lens, significantly impacting visualization. Furthermore, it can be difficult to discern if coating residue is new or old. Because of that, you may consider including sips of clear water to assist in clear coating. You may also consider alternating bolus with coating with boluses that have minimal-to-no coating effect, and also altering between different colors to help discern which residue is from which bolus trial.

For opaque-colored liquids, I recommend using water, green or blue dye (to give it color), and a little bit of white dye (to make it opaque). Limiting the white dye to just a few drops should not elicit a significant coating effect. Using water avoids pragmatic issues associated with using milk (e.g., dietary restrictions, refrigeration, costs). Using opaque-colored liquids with minimal-to-no coating effect will help to wash away coating on the mucosa and camera lens from previous trials. Because the bolus is colored green/blue, it will be easier to discern new residue is new (blue/green) from coating-related residue (white). And because the bolus is opaque, it will maximize the sensitivity and reliability compared to using something completely translucent. You may also consider integrating sips of clear water between liquid trials to clear residue from previous swallows an ultimately enhance accuracy of FEES interpretation.

For puree boluses, I recommend using pudding, since this more closely resembles the consistency also used during VFSS. Chocolate pudding may be avoided since it is darker and more difficult to visualize. Vanilla pudding is more easily visible, but can be difficult to discern from thick secretions or white liquid residue. Therefore, you may consider adding food dye to help discern pudding residue from secretions and liquid residue.


(Standardized recipe last updated January 30th, 2022)


  • Chef-O-Van Food Coloring, Green

  • Chef-O-Van Food Coloring, Blue

  • Chefmaster Liquid Whitener Food Color, White Liquid; or AmeriColor Soft Gel Paste Food Color, Bright White

  • Two eyedropper bottles

  • Snack Pack Vanilla Pudding (3.25 ounce cups)

  • Saltine crackers

  • Food scale

  • 8-ounce Measuring cups

  • Medicine Cups

  • Syringes

Thin Liquids (IDDSI 0)

      • Fill one 8-ounce cup up with 148 mL of water, then add 1 mL of white dye and 20 drops of green dye (this is ~1 mL, or ~2 full plunges from the eyedropper)

          • This will be for 10 mL, 20 mL, and patient-preferred volume thin liquid sip swallowing conditions

          • This will be liquid that is colored, opaque, with minimal coating effect

      • Fill a second 8-ounce cup with 144 mL of water, then add 6 mL of white dye

          • This will be for 10 mL, 20 mL, and patient-preferred volume thin liquid sip swallowing conditions

          • This will be a heavily-concentrated white-dyed liquid that is opaque with prominent coating effect

      • Fill a third 8-ounce cup with 87 mL of water, then add 3 mL of white dye

          • This will be for a 90 mL, serial liquid swallow condition

      • After adding the colorants, stir each cup with syringe for ~2-3 seconds, then complete at least five plunges with a syringe for each cup. Stir and plunge additionally as needed until well mixed.

      • Stir and plunge each cup immediately before administering during the FEES, especially if a few minutes have lapsed between setup and start time, to ensure the coating property is "activated"

      • Alternate between the “white coating” and the “green opaque” liquid boluses to help discern residue patterns between each trial

Thickened Water (IDDSI 2-3)

  • Add thickening powder to cup

  • Then add 1 mL of white dye and 20 drops of blue or green dye

  • Then slowly add 150 mL of running water into the cup while stirring continuously (this should take about 10-20 seconds)

  • Continue stirring for 15 seconds, followed by 15 seconds of plunging

Extremely thick (IDDSI 4)

  • Open a 3.25 ounce container of vanilla pudding – we use the SnackPack Vanilla Pudding

      • We use pudding as opposed to applesauce, because we’ve found applesauce consistency can vary significantly across brands (ranging from very thick to a bit waterier)

      • We use pudding because it is also more representative of barium pudding used for videofluoroscopy (i.e., greater generalization between FEES and VFSS)

  • Add 20 drops (~two full plunges from an eyedropper) of blue dye

      • We use vanilla pudding because it is white, making it more easily visible on endoscopy compared to chocolate pudding

      • We color the vanilla pudding with blue/green dye to help distinguish it from secretions, white dyed liquid, and saltines

      • If dying the water blue, then you may consider using green dye for the pudding to avoid confusion with liquid residue. If using green dye for water, then you might use blue for the pudding.

  • Stir with a smooth until the color is mixed well with the pudding

Additional Notes

  • I typically add white dye directly into a 10 mL syringe, then I syringe the 1, 6, and 3 mL of white dye into each cup from the same syringe

  • I do not endorse or have any financial relationship with the products outlined above, however for transparency and reproducibility, we are being specific with what we use and what you may consider also using

  • The concentration of food coloring could change across brands, so be aware of this if using brands other than what we’ve highlighted here

  • Consider purchasing a large amount of food coloring (e.g., 16 ounce), and pouring into smaller eye droppers for quicker and more efficient use during preparation


  1. Curtis, J. A., Seikaly, Z. N., Dakin, A. E., & Troche, M. S. (2021). Detection of aspiration, penetration, and pharyngeal residue during flexible endoscopic evaluation of swallowing (FEES): comparing the effects of color, coating, and opacity. Dysphagia, 36(2), 207-215

  2. Curtis, J., Perry, S., & Troche, M. S. (2019). Detection of airway invasion during flexible endoscopic evaluations of swallowing: comparing barium, blue dye, and green dye. American journal of speech-language pathology, 28(2), 515-520

  3. Butler, S. G., Stuart, A., Markley, L., Feng, X., & Kritchevsky, S. B. (2018). Aspiration as a function of age, sex, liquid type, bolus volume, and bolus delivery across the healthy adult life span. Annals of Otology, Rhinology & Laryngology, 127(1), 21-32

  4. Marvin, S., Gustafson, S., & Thibeault, S. (2016). Detecting aspiration and penetration using FEES with and without food dye. Dysphagia, 31(4), 498-504.

  5. Leder, S. B., Acton, L. M., Lisitano, H. L., & Murray, J. T. (2005). Fiberoptic endoscopic evaluation of swallowing (FEES) with and without blue-dyed food. Dysphagia, 20(2), 157-162.