Does the smell of frying linger in the kitchen before spreading to the living room, or does it arrive as soon as cooking begins? A 2008 study fried potatoes in an experimental open-plan living, dining, and kitchen space and tracked changes in the odor people perceived. Under these conditions, odor tended to intensify first in the kitchen with induction heating, while spreading relatively quickly to the living and dining areas with gas.
The main aim was not to rank heat sources, but to develop a method for measuring indoor changes with a human nose that becomes accustomed to odors. The researchers aligned ratings using reference odors, gave noses rest periods, and compared the results with temperature, humidity, and smoke movement.
Using odor samples to establish a shared meaning of strong
The odor evaluated was oil-fume odor from frying potatoes in rapeseed oil. Researchers first analyzed compounds produced by cooking under the same conditions and selected 2,4-decadienal, which they identified as a major constituent, as the reference odor. It has a smell reminiscent of fried food.
The rating scale ran from 0 to 3, from odorless to a strong odor, divided into seven levels at 0.5 intervals. Three people found to have normal olfactory function repeatedly learned reference odors of different concentrations and their corresponding intensities. The intention was to align ratings through shared examples rather than relying only on a word such as strong.
For two participants who underwent more training, the proportion identifying the correct intensity increased from just under 40% initially to over 70% later. The other participant, who completed fewer trials, had a 32% correct-response rate, rising to 63% if an adjacent scale level was accepted. Training helped, but the three participants’ accuracy was not completely aligned.
Resting the nose reduced the decline in ratings
When someone continually smells the same odor, it can seem weaker even while it remains in the room. Having assessors repeatedly leave, however, interrupts measurement and may alter airflow as doors open and close.
The researchers therefore tested a one-minute rest with a cotton handkerchief folded into quarters held over the nose. In a preliminary experiment, ratings after cooking declined less when rest periods were included than when they were not. The sum of post-cooking ratings also differed between 10 records with rest and seven without. These case counts refer to experimental rating records, not a comparison of 17 people.
Longer intervals between rests also tended to produce greater rating declines. In the main experiment, one-minute rests were therefore introduced every two minutes from 15 minutes after the start. The authors considered this an effective way of reducing adaptation to the odor. Because measurement was impossible during rest, however, those intervals were assigned the rating recorded immediately after the handkerchief was removed.
Cooking the same food and tracking it in three areas
The main experiment took place in an open-plan living, dining, and kitchen space in an experimental building in Osaka. The cooking setup involved boiling water and frying simultaneously. Using 1,000 mL of rapeseed oil, researchers fried three 100 g batches of potatoes. There were eight induction-heating experiments and six gas experiments, with oil temperature, heating time, and exhaust airflow standardized. Exhaust airflow was 400 cubic meters per hour.
One of the three assessors was positioned in each of the kitchen, dining, and living areas, with their seated noses approximately 120 cm above the floor. They adjusted a dial to indicate perceived intensity, which the device recorded every two seconds. Ratings concerned odor intensity, not liking or unpleasantness.
Reference-odor checks before and after the main experiment found correct-response rates of approximately 70% for two assessors and approximately 40% for the third. One assessor had a statistically significant difference in rating error before versus after the experiment. Scale alignment offered some help, but could not be said to eliminate individual differences or drift over time.
Induction spread from the kitchen; gas reached adjacent areas quickly
In five of the eight induction experiments, kitchen ratings were high during cooking. In another, kitchen and dining ratings were high while the rise in the living area was somewhat delayed. Although results varied considerably between experiments, odor generally began later than with gas and tended to spread through the kitchen before reaching adjacent areas.
With gas, in five of the six experiments, dining or living-area intensity equaled or exceeded kitchen intensity early after cooking began. Dining-area ratings also remained high after cooking in all six experiments. The researchers suggest an airflow pattern that transports odor quickly into adjacent areas and subsequently allows it to linger around the dining area.
To examine the difference by another method, the researchers measured room temperature and humidity and observed smoke generated under matching conditions using laser light and video. With induction, smoke slowly spread through the kitchen before moving toward the adjacent space. With gas, a strong updraft transported smoke quickly, and smoke not captured by the exhaust fan spread from above into the living and dining areas. It was also seen descending after meeting incoming air and remaining near nose height in the dining area.
Under gas conditions, temperature and humidity increases were greater in the upper part of the room; induction produced relatively uniform temperature changes. The many points of agreement between these observations and the time course of perceived odor provide the main support for the proposed measurement method.
What was measured was dispersion in this particular room
Because each of the three assessors occupied a fixed location, location differences and individual perceptions overlapped. Cooking movements were screened from view, but sound was audible during the main experiment and participants were told beforehand which heat source would be used. Smoke visualization checked airflow rather than directly measuring the concentration distribution of odor compounds.
The comparison also involved one experimental room with standardized ventilation, oil temperature, and heating time. Different layouts, supply-air openings, range hoods, or dishes could change the flow. The speed at which odors arrived here cannot determine whether induction or gas produces fewer total emissions or greater comfort in homes.
Summary
In this experiment, oil-fume odor with induction tended to intensify first in the kitchen. With gas, it reached the living and dining areas quickly and tended to remain in the dining area after cooking. Human ratings corresponded with temperature, humidity, and smoke observations, providing clues for tracking changes in indoor odor.
Methodologically, sharing an intensity scale through reference odors and giving the nose rests were useful. Measuring cooking odors requires attention not only to how odors travel, but also to how the assessor’s nose adapts. That is an important contribution of this study.
Research affiliations: At the time of the research, three authors were affiliated with Kansai Electric Power and two with the Central Research Institute of Electric Power Industry. No separate research-funding or conflict-of-interest declaration was found.
Reference
Igarashi Y, Banba I, Yagi Y, et al. Proposal of Simple Method about Continuous Organoleptic Evaluation of Oil Odor Diffusion on Cooking. Journal of Environmental Engineering (Transactions of AIJ). 2008;73(627):623–630. doi:10.3130/aije.73.623
