Kaolid: Lid-type Olfactory Interface to Improve
Taste of Beverages with Ortho-Retronasal Smell
Daiki Mayumi1 , Yugo Nakamura2 , Yuki Matsuda1 , Kentaro Ueda1 , Shinya Misaki1 , Keiichi Yasumoto1
1

Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
Email: {mayumi.daiki.mb9, yukimat, yasumoto}@is.naist.jp
2
Kyushu University, Fukuoka, Fukuoka 819-0395, Japan
Email: y-nakamura@ait.kyushu-u.ac.jp

Abstract—There are two nasal pathways through which weperceive odors: “orthonasal smell,” which comes from the tip ofthe nose, and “retronasal smell,” which comes from the mouthand exits through the nose. In particular, the retronasal smell
is known to be more critical in influencing perceived taste thanthe orthonasal smell. In this study, we propose a smart lid called
Kaolid that changes the taste of beverages by presenting scentinformation as retronasal smell. Kaolid achieves retronasal smell
by equipping a small, lightweight straw- or cup-type olfactory
device with a sensor that senses drinking behavior and theamount of water in the cup. The straw-type device injects thescent into the tube through the middle of the straw, delivering
the scent to the user’s mouth simultaneously as the beverage isbeing consumed. The cup-type device injects the scent into thecup through the lid and delivers the scent to the user’s mouth
at the beginning of drinking to achieve in-mouth scenting. The
concept of Kaolid is to promote water consumption, considered
insipid, by altering the sense of taste through a scent presented
when drinking the beverage.
Index Terms—Olfaction, Olfactory Interfaces, Olfactory display, Scents, Taste evaluation, Smell, Olfactory Perception

I. I NTRODUCTION
Sweetened beverages have become a major source of sugarin our diets. Sugar-sweetened beverage consumption has increased dramatically, particularly in developing countries [1],[2], resulting in a significant annual increase in the number ofdiabetic patients worldwide [3].
Several methods have been proposed to help people reduce
their sugar intake [4], [5]. These methods can temporarily
encourage the selection of less-sugar soft drinks to reducesugar intake. However, less-sugar or unsweetened water isoften unpalatable. Therefore, a temporary intervention will
not last long and will likely result in a return to the previous
lifestyle of regularly drinking sugary drinks. From a well-being
perspective, finding solutions to gradually reduce the amountof sugar consumed is essential, as extreme reductions in sugar
intake can lead to emotional distress for the user [6].
In recent years, various types of olfactory devices have been
proposed along with interactions in using these devices [7]–[11]. These studies propose wearable devices worn around theneck and on-face olfactory devices worn on the face in theform of earrings or necklaces, which can be used in daily life.
There are also studies that have developed digital devices thatmimic actual beverages by activating electrical and olfactory(scent) stimuli together [12], [13]. However, the approach toFig. 1. Overview of Kaolid ((a)Straw-Type Device, (b)Cup-Type Device)scent is limited to the orthonasal smell, and the effect ofthe different nasal pathways used to perceive scent on theperceived taste is unclear.
There are two types of scents that we perceive: the “orthonasal smell,” which comes from the tip of the nose, andthe “retronasal smell,” which is the smell of food in the mouththat passes through the nose, and each smell is processed by
the brain in a different way [14]–[16]. In particular, retronasal
smell, which contributes to the flavor of food and beverages,
is known to be strongly related to the sense of taste [17].
Focusing on the fact that scent accounts for the majority ofwhat is perceived as taste, we have been developing a mugtype olfactory device that amplifies the perceived sweetnessby presenting a sweet smell when drinking a beverage [18].
However, the approach is limited to the presentation of orthonasal smell and does not present retronasal smell, which
may be insufficient in promoting changes in taste perception.
In this study, we propose a smart lid called “Kaolid”* thatchanges the taste of beverages by targeting the retronasal
smell in presenting scent information when the beverage isconsumed. Kaolid is either a straw or cup-type small andlightweight olfactory device as shown in Fig. 1. To promotewater consumption, Kaolid uses a straw-type device for drinking cold water or water at room temperature and a cup-typedevice for drinking plain hot water. The straw-type device
injects the scent into the tube through the middle of the straw,
delivering the scent to the user’s mouth simultaneously as thebeverage is being consumed. The cup-type device injects thescent into the cup through the lid and delivers the scent tothe user’s mouth at the beginning of the drinking operation toachieve in-mouth scenting.
* Inspired from “Kaori” meaning smell in Japanese.

Fig. 2. Device Design of Kaolid

II. OVERVIEW OF K AOLID
A. Approach
Consumption of sugar-free beverages is important for reducing sugar intake. However, people who are used to sugarsweetened beverages are likely to be uncomfortable withodorless, tasteless water.
Therefore, following the finding that a considerable partof taste perception is influenced by scent [19], to change
the taste of water, we present scent information in a welltimed manner in conjunction with drinking movements. The
proposed olfactory interface called “Kaolid” is equipped witha sensing function for the act of drinking and a presentation
function for scent information that changes the sense of taste.
B. System Design
1) Mechanism of Scent Injection: A pneumatic pump
(MZB1001T02† ) was used as the mechanism to inject thescent. The pneumatic pump is a device that draws air fromone side and discharges air from the other side. The pneumatic
pump used in this study is based on the principle of apiezoelectric diaphragm pump and achieves high pressure andflow rates despite its small size and thin profile by applying
ultrasonic vibration.
As shown in Fig. 2, a pneumatic pump and a circuit driving
the pump are installed inside a container created by a 3D
printer. The power source voltage is boosted by a buck-boost
converter to drive the pneumatic pump. In the pneumatic
pump, the output pressure varies depending on the input
voltage. The input voltage is proportionally related to the airpressure of the pneumatic pump mounted on this device. In
this device, the input voltage to the pneumatic pump is set to
15 V, and the air pressure is approximately 1.6 kPa. This airpressure is sufficient for producing a faint scent at a distanceof approximately 30 cm from the device. Aroma oil is used as
the scent, and the container is filled with cotton that has been
soaked with the scent. The pneumatic pump is used to inject
the scent that has been filled in the container.
2) Prototype of Kaolid: In this study, we created a strawtype device and a cup-type device to change the taste ofbeverages by presenting scent information to the mouth. The
straw-type device, shown in Fig. 1 (a), has a separate opening† https://www.murata.com/ja-jp/products/mechatronics/fluid/overview/lineup/microblower mzb1001t02

Fig. 3. Experimental resultsfrom the center of the straw, which injects scent into the straw.
As a result, the device can deliver scent to the mouth andproduce a retronasal smell. The cup-type device, shown in
Fig. 1 (b), has a device that injects scent into the upper partof the cup to deliver scent into the mouth during drinking,thus producing a retronasal smell.
3) Experiment: To investigate the effect of Kaolid on taste,
a preliminary experiment was conducted on 11 participants (7males and 4 females), ranging in age from 10 to 70 (mean= 37.3). Pineapple, orange, and muscat were used for scent,and room temperature water was used as the beverage. To
prevent possible bias arising from the order of the devices usedin the experiment, six different experiments were conducted,
each with a different order of devices. After each experiment,
the participants were asked to answer a questionnaire about
their tasting experience. The questionnaire, utilizing a 9-point
hedonic scale, asked respondents to answer the following
four items (Q1: taste satisfaction, Q2: taste sweetness, Q3:
taste preference, Q4: taste difference). In Q4, we evaluatedthe change in the taste of the water drank with Kaolid
compared to water without scent. Therefore, Q4 could not
be evaluated in the experiment without scent. Fig. 3 shows
the mean and standard deviation of the questionnaire results.
It was confirmed from Q2 that the sweetness of the taste wasconsiderably amplified by the use of Kaolid compared to water
without scent. From Q3 and Q4, it was confirmed that the tasteof the straw-type device was more changeable, but there was apreference for the cup-type device over the straw-type device.
This is presumably because the mechanism of the straw-typedevice, sending air into the straw, is difficult to use.
C. Implementation
Kaolid consists of a mechanism that sprays scent, abeverage-sensing mechanism, and a sensor that detects theamount of water in the cup, as shown in Fig. 2. The sensing mechanism of the beverage is equipped with an IMU

sensor (MetaMotionR+: sensors – 100 Hz quaternion threeaxis accelerometer/gyroscope; dimensions - L29 × W18 × H6
mm; weight - 5.7 g), as shown in Fig. 2. The IMU sensor
signals are transmitted to the gateway device via Bluetooth
Low Energy (BLE). The gateway device analyzes the IMU
sensor signals and recognizes the user’s drinking behavior.
It performs time-series signal processing and controls themechanism that sprays the scent. First, the attitude angle ofthe device is calculated from the acceleration and gyro signals
obtained from the IMU sensor. The system recognizes threeactions (lifting the cup, drinking, and releasing the cup), as
constituting beverage behavior, based on the acceleration dataand gyroscope sensor data. Currently, the beverage drinking
time is determined by a threshold value, but in the future, amachine learning model that recognizes timing will be used.
The signal from the IMU sensor recognizes the beveragedrinking time and activates the pump so that the scent issprayed. The device also has a water level sensor that detects
the amount of water in the cup. A variable resistor is mounted
on the water level sensor with the resistance value changing
according to the amount of water. Specifically, the change inthe sensor is inversely proportional to the depth to which
it is immersed in water. This mechanism logs the numberof beverages consumed by the user throughout the day. In
the future, the system will be equipped with a module thatrecognizes the kind of beverage poured into the cup [20].
Checking the beverage log by the user contributes to a better
understanding of healthy beverage intake.
III. K AOLID DEMONSTRATIONIn the demonstration, the participants experience how theKaolid changes the taste of water. As shown in Fig. 1, an inmouth aroma is produced, and the scent achieves the change
in taste. Scents are selected from a group of 10 odors thathumans can perceive, with the citrus group considered to becompatible with water [21]. Kaolid enables users to easilychange scents and experience a variety of tastes depending on
the type of scent. By changing the taste according to the scent,the user feels satisfied with the tasteless water and is expected
to increase the amount of water consumed. Kaolid can also
estimate the amount of water in the cup using a water levelsensor. The user can check the water intake log to see whenand how much beverage has been consumed over medium tolong term. Kaolid is expected to contribute to the developmentof healthy and adequate hydration habits.
ACKNOWLEDGMENT
This work was supported by JST, PRESTO Grant Number
JPMJPR21P7, Japan.
R EFERENCES[1] World Health Organization, “Diabetes,” Available online:
https://www.who.int/news-room/fact-sheets/detail/diabetes,
accessed:
2022-02-25.
[2] M. B. Schulze, J. E. Manson, D. S. Ludwig, G. A. Colditz, M. J.
Stampfer, W. C. Willett, and F. B. Hu, “Sugar-sweetened beverages,
weight gain, and incidence of type 2 diabetes in young and middle-aged
women,” Jama, vol. 292, no. 8, pp. 927–934, 2004.

[3] W. H. Organization, “Diabetes,” https://www.who.int/news-room/factsheets/detail/diabetes, 2021, accessed: 2022-02-25.
[4] J. Hoenink, J. Stuber, J. Lakerveld, W. Waterlander, J. Beulens, andJ. Mackenbach, “The effect of on-shelf sugar labeling on beverage sales
in the supermarket: a comparative interrupted time series analysis of anatural experiment,” ISBNPA, vol. 18, no. 1, pp. 1–11, 2021.
[5] K. Villinger, D. Wahl, K. Engel, and B. Renner, “Nudging sugar
portions: a real-world experiment,” BMC nutrition, vol. 7, no. 1, pp.
1–5, 2021.
[6] J. S. Gonzalez, S. A. Safren, E. Cagliero, D. J. Wexler, L. Delahanty,
E. Wittenberg, M. A. Blais, J. B. Meigs, and R. W. Grant, “Depression,
self-care, and medication adherence in type 2 diabetes: relationships
across the full range of symptom severity,” Diabetes care, vol. 30, no. 9,
pp. 2222–2227, 2007.
[7] T. Yamada, S. Yokoyama, T. Tanikawa, K. Hirota, and M. Hirose,“Wearable olfactory display: Using odor in outdoor environment,” inIEEE Virtual Reality Conference (VR 2006). IEEE, 2006, pp. 199–
206.
[8] J. Amores and P. Maes, “Essence: Olfactory interfaces for unconscious
influence of mood and cognitive performance,” in Proceedings of the2017 CHI conference on human factors in computing systems, 2017,
pp. 28–34.
[9] D. Dobbelstein, S. Herrdum, and E. Rukzio, “inscent: A wearable olfactory display as an amplification for mobile notifications,” in Proceedingsof the 2017 ACM International Symposium on Wearable Computers,
2017, pp. 130–137.
[10] Y. Wang, J. Amores, and P. Maes, “On-face olfactory interfaces,”in Proceedings of the 2020 CHI Conference on Human Factors in
Computing Systems, 2020, pp. 1–9.
[11] Y. Choi, R. Parsani, X. Roman, A. V. Pandey, and A. D. Cheok, “Soundperfume: building positive impression during face-to-face communication,” in SIGGRAPH Asia 2012 Emerging Technologies, 2012, pp. 1–3.
[12] N. Ranasinghe, G. Suthokumar, K.-Y. Lee, and E. Y.-L. Do, “Digitalflavor: towards digitally simulating virtual flavors,” in Proceedings ofthe 2015 ACM on international conference on multimodal interaction,
2015, pp. 139–146.
[13] N. Ranasinghe, M. N. James, M. Gecawicz, J. Bland, and D. Smith,“Influence of electric taste, smell, color, and thermal sensory modalities
on the liking and mediated emotions of virtual flavor perception,”in Proceedings of the 2020 International Conference on MultimodalInteraction, 2020, pp. 296–304.
[14] S. Heilmann and T. Hummel, “A new method for comparing orthonasal
and retronasal olfaction.” Behavioral neuroscience, vol. 118, no. 2, p.
412, 2004.
[15] D. M. Small, J. C. Gerber, Y. E. Mak, and T. Hummel, “Differential neural responses evoked by orthonasal versus retronasal odorant perception
in humans,” Neuron, vol. 47, no. 4, pp. 593–605, 2005.
[16] V. Bojanowski and T. Hummel, “Retronasal perception of odors,”
Physiology & behavior, vol. 107, no. 4, pp. 484–487, 2012.
[17] P. Rozin, “” taste–smell confusions” and the duality of the olfactory
sense.” Perception & psychophysics, 1982.
[18] D. Mayumi, Y. Nakamura, S. Misaki, Y. Matsuda, and K. Yasumoto,“Aromug: Mug-type olfactory interface to assist in reducing sugar
intake,” in The 5th International Workshop on Computing for Well-Being(WellComp ’22), 2022.
[19] B. Lyman, A psychology of food: More than a matter of taste. Springer
Science & Business Media, 2012.
[20] Y. Huang, K. Chen, Y. Huang, L. Wang, and K. Wu, “Vi-liquid: unknown
liquid identification with your smartphone vibration,” in Proceedings ofthe 27th Annual International Conference on Mobile Computing and
Networking, 2021, pp. 174–187.
[21] J. B. Castro, A. Ramanathan, and C. S. Chennubhotla, “Categoricaldimensions of human odor descriptor space revealed by non-negative
matrix factorization,” PloS one, vol. 8, no. 9, p. e73289, 2013.