COMPARING INFRARED AND PROBE THERMOMETERS TO MEASURE THE HOT

HOLDING TEMPERATURE OF FOOD IN A RETAIL SETTING

Rohit C., Moos M., Meldrum R., Young I.

School Of Occupational and Public Health, Ryerson University

• The fundamental technical difference between probe and

infrared thermometer is that infrared thermometer

provide the surface temperature of the food item whereas

the probe thermometer offers the internal temperature.

• Food safety regulations in Ontario for the food service

and retail sector requires that potentially hazardous food

that is kept hot must be held at an internal temperature of

≥60°C. This limits the use of an infrared thermometer for

food safety compliance.

• This research examines the relationship between the

internal temperature of the hot holding food measured

via probe thermometer and the surface temperature

measured via infrared thermometer in a retail setting.

BACKGROUND

PURPOSE

• Seven different stores (Store A to Store G) from one

major retail chain in Greater Toronto Area were visited

six times each during February and March 2018.

• Seven different hot held food items (whole chicken,

chicken strips, chicken pieces, breaded chicken wings,

honey garlic chicken wings, potato wedges, ribs) were

sampled twice for internal temperature via probe

thermometer and twice for the corresponding surface

temperature via infrared thermometer during each visit.

• Both types of measurements were taken using a ParTech

TMD (ParTech, Inc. Toronto).

• The sampling time and store cooking time record were

used to calculate a variable ‘elapsed time’ – amount of

time a food product setting in the hot hold unit. Other

variables included in the research were total quantity of

food items in the hot holding unit (number of food

boxes), temperature of the hot-holding unit, and outside

weather temperature (via the Weather Network mobile

app).

• The data were analyzed using Microsoft Excel and SPSS

software.

Figure 1 Figure 2

Figure1: This graph shows probe measurement values for given infrared values at each sample point. At

the lower infrared temperatures (<60°C), the internal temperature is usually higher, and at the higher

temperature level, the effect is inversed. This can be explained by the surface of the food cooling down

faster in comparison to the center of the food.

Figure 2: This graph shows the strong positive correlation between the probe temperature and the

infrared temperature.

MATERIALS AND METHODS

• The Pearson Correlation test shows a significant

positive correlation (r = 0.706, n = 212) between the

probe and infrared measurements.

• The correlation between the probe and infrared

measurements differed among the food items, with

breaded chicken wings having the highest correlation (r

= 0.867, n = 35) and potato wedges having the lowest

correlation (r = 0.592, n = 39)

• The correlation between the two thermometer types

also differed by store.

• The elapsed time variable (preparation time – sampling

time) had a negative correlation with both the probe (r

= -0.261, n = 182) and infrared (r = -379, n = 182)

measurements.

RESULTS

DISCUSSION

• The research showed a strong positive correlation

between the probe and infrared thermometers and that

indicate a possibility of developing a predictive model

to estimate the internal temperature of food via

infrared thermometers.

• Such a model will make the use of infrared

thermometers more reliable for food safety

compliance by the food service industry.

• The elapsed time had a negative correlation with both

the probe and infrared temperatures and the result

suggests that longer the food stays in the hot holding

unit the more likely that it will have lower

temperature.

• The research had some limitations, including use of

only one type of thermometer, one retail chain, and

limited types of food products.

DESCRIPTIVE ANALYSIS OF STUDY

VARIABLES FOR ALL FOOD ITEMS

Mean SD N

Hot Holding Unit

Temp(°C) 74.64 10.69 33

Hot Holding Unit Food

Quantity21.53 9.75 43

Time Elapsed(h:mm) 1:59 1:32 182

Probe Temp(°C) 66.05 6.38 212

Infrared Temp(°C) 64.95 9.19 212

Difference b/w Probe &

Infrared(°C) 5.38 1.10 212

Outside Temp(°C) 1.76 3.30 294

PEARSON CORRELATION BETWEEN EXPLANATORY VARIABLES AND TEMPERATURE

MEASUREMENTS

VariableProbe Infrared

r p N r p N

Hot Holding Unit Temp -0.109 0.171 159 -0.293 0.01 159

Hot Holding Unit Food Quantity 0.021 0.766 212 -0.131 0.58 212

Time Elapsed -0.261 0.01 182 -0.379 0.01 182

Outside Temp 0.053 0.439 212 0.059 0.396 212

CORRELATION BETWEEN THE PROBE AND

INFRARED TEMERATURES, STRATIFIED BY

FOOD TYPE AND STORE LOCATION

Variable r p N

Food Type

Whole Chicken 0.741 0.01 42

Chicken Stripes 0.837 0.01 32

Chicken Pieces 0.756 0.01 36

Breaded Chicken Wings 0.867 0.01 35

Honey Garlic Chicken Wings 0.677 0.01 27

Potato Wedges 0.592 0.01 39

Ribs - - 1

Store Type

Store A 0.569 0.01 35

Store B 0.744 0.01 26

Store C 0.866 0.01 35

Store D 0.531 0.01 28

Store E 0.603 0.01 26

Store F 0.907 0.01 29

Store G 0.719 0.01 31

All data 0.706 0.01 212