How Does Temperature and Humidity Affect the Physical State of Hard Candy During Storage?
Katherine M. Labuza St. John The Baptist School New Brighton, MN; P. Zhou and T.Labuza, Food Science & Nutrition, Univ. of Minnesota USA
Procedures
Abst
ract
Hard Candies are formed from boiled sugar solutions (≥ 250°C)
which are poured into a mold and cooled, forming a glassy hard
mass. Such candy is subject to development of stickiness due to
both temperature and humidity increases. This study was
conducted to determine both the temperature and humidity effect on
a hard candy. Altoids ® purchased from a food broker were stored
for three days at four constant relative humidities (11%, 33%, 45%
and 75%) both open and closed with and without the original seal.
These were then introduced into abuse temperature conditions of
35, 45, 55 and 65 °C for 12 hours (all closed). The Altoids ® were
evaluated by rating each can (duplicates) using a tactile sensory
scale (1 to 5). Digital images were taken to document the score. A
glass transition curve and melt curve was determined by DSC as a
function of the %RH of original storage. The results demonstrated
that below the glass transition curve, the Altoids ® candies did not
change state and came easily out of the can. At room temperature
the hard candy remained stable at ≤ 33% RH, above that they
became sticky with the sealed can giving slightly more protection
than an open can. Temperature abuse above the glass transition line
caused the candy to get sticky at all conditions. At 55 and 65 °C,
possible in an closed car in the sun, the candy structure collapsed
and flowed to form a single hockey puck in the can. Thus the
warnings on Altoids ® to “Store in a cool dry place” and “Replace lid
between use” have real meaning, ie. don’t leave them in a closed
car in the sun during the summer. The results suggest that
temperature has a greater effect than humidity.
Background
Hard candy is made by boiling a solution of sugar
and corn which is then rapidly cooled in a mold
without crystallizing to form a hard candy. This candy
in in a physical state as a hard non-sticky amorphous
solid at room temperature and low humidity. However,
if the candy is abused by a high temperature or
humidity or both, the product becomes sticky and
lumps together, a consumer complaint. For example
the Altoids® label says it should be stored in a “cool,
dry place,” indicating that Altoids are not completely
stable at high temperatures and high humidities. A
question to form from this information is which causes
more damage to the product, high temperature (T) or
high humidity (%RH). For example data from the
literature shows that cars left in the sun (Figure below,
McLaren and others) can increase to almost 60°C.
Labuza and Labuza (2004) indicated that the glass
transition curve ( Tg vs %RH representing the change
from an amorphous glassy (hard candy) to a rubbery
or sticky state) is a good map for indicating where
stickiness, collapse and flow (not true melting) of a
candy material, in this case cotton candy can occur.
Although the concept Tg vs %RH has been applied to
high sugar containing powders like infant formula, no
one has studied the effect of %RH and T abuse. In
this case if the surface of the candy goes above the
Tg line adverse effects should begin to occur.
Vehicle Temperature Rise Over Time
Hypot
hesi
s
Increasing the temperature and/or humidity during
storage will change the physical state of hard candy
adversely affecting the quality of the product. The extent
of change will be controlled by the position above the
glass transition temperature line (Tg vs %RH).
1 .Obt
ai
n1 0 0
f
ood
broker.Creat
ef
ourhumi
di
t
ychambers(
1 1 , 3 3 , 4 5 , and7 5 %
rel
at
i
ve humi
di
t
y)usi
ng speci
f
i
csat
urat
ed sal
tsol
ut
i
ons.
Pl
ace 1 0 seal
ed, 1 0 unseal
ed(
removalofpl
ast
i
cwrappi
ng
f
rom around l
i
d)butcl
osed and1 0 unseal
ed andopen
cont
ai
nersoft
he hard candyi
nt
ot
he f
ourrel
at
i
ve humi
di
t
y
chambers.
2 .Eval
uat
et
he ef
f
ect
ofhumi
di
t
yabuse over
at
hreedayperi
od of
t
i
me and documentby
t
aki
ng pi
ct
uresand
usi
ng t
he f
ol
l
owi
ng
t
act
i
l
e sensoryscal
e
f
ordat
a.
Di
scussi
on Poi
nt
s
3 .St
udyt
he ef
f
ectof
t
emperat
ure abuse af
t
era
t
wel
ve hourperi
odatf
our
di
f
f
erentt
emperat
ures(
35,
4 5 , 5 5 , and 6 5 °C)by
f
ol
l
owi
ng t
he same t
act
i
l
e
scori
ng asi
n procedure2 .
Altoids in storage Humidity
Chambers at 11%, 33%, 58%,
and 75% RH for ~ 3 days
Resul
t
s
2
Very sticky
but will fall
out
3
In the results shown above, the sensory tactile score at each T-%RH
condition was indicated on top the the Tg curve. In reviewing this and the true
melt plot it is observed that:
1. Hard candies like Altoids ® are an amorphous glassy material, which
initially shows a state in which the candies are free flowing and can be easily
picked out of a can. Initial aw of candy ~ 0.11
EXAMPLE HUMI
DI
TY EFFECT
1 1 % RH 2 3 °C
7 5 % RH 2 3 °C
SENSORY TACTI
LE SCORI
NG SCALE
Loose
Somewhat
and Dry Sticky
1
5 . Revi
ew t
he resul
t
sofphysi
calchangesascompared t
o publ
i
shed dat
a on i
nsi
de
t
emperat
ure ofaut
omobi
l
eson hotsummerdaysasnot
ed above aswel
last
he
sci
ent
i
f
i
cdat
a ofcol
l
apse and cryst
al
l
i
zat
i
on ofcot
t
on candy, anot
herconf
ect
i
onery
Labuza and Labuza, 2 0 0 4 )
.Det
ermi
ne i
fhumi
di
t
yor
productmade f
rom sugars(
t
emperat
ure changecausesa great
eref
f
ecton t
he i
nst
abi
l
i
t
yofhard candy.
cansofhardcandy(
Al
t
oi
ds®)f
rom
Extremely Flows together
Sticky and so that structure
will not fall is completely
out
gone
4
2. Such candies are subject to stickiness when exposed to abuse
temperatures and when stored at higher humidities or both . This can occur
when stored in a closed car directly exposed to the sun where temperatures can
increase the inside air temperature up to 55 °C to 65 °C
Score= 1
Score= 4 .5
Open cans@ 2 3 °C f
or3 days
3. The glass transition curve (Tg vs. %RH) can be used to define the dividing
line for optimal storage conditions where below this line the candies are
separate and non sticky while above the line the hard candies go through
various sticky and flow states.
TEMPERATURE EFFECT @ 3 3 % RH
5
35 C
score= 1
45 C
score= 4
55 C
score= 4
65 C
score = 5
Procedures 2
and 3:
Showing the
testing of
humidity and
temperature
abuse.
4. Closed cans with or without the original seal gives some protection to
humidity at 33% RH but increases in temperatures to ≤ 45 C, they become a
little sticky but shaking the can separates the individual hard candies. However
unopened cans with or without a seal demonstrates that temperature rise to 55
or 65 °C, has a greater detrimental effect than an increase in %RH to 75
5. At all %RH, storage temperatures of 55 °C (131° F) and 65 °C ( 149 C),
which is possible in a closed car in the sun during summer, cause a serious
physical state change including complete flow and collapse to form a hockey
puck like structure, well below the crystal melt temperatures of 110 to 120°C.
Concl
usi
on
4 .W orkwi
t
h Dr.Peng Zhou att
he Uni
versi
t
yofMi
nnesot
at
ol
earn
how t
o do Di
f
f
erent
i
alScanni
ng Cal
ori
met
ry(
DSC)on t
he candy
sampl
esst
ored att
he di
f
f
erentpercent
age rel
at
i
ve humi
di
t
i
esat
room t
emperat
ure condi
t
i
onst
o det
ermi
ne amorphousversus
l
i
ne st
at
e change ofmat
t
er. From t
hi
sprepare t
he gl
ass
cryst
al
t
ransi
t
i
on curve.To do t
hi
s, t
he procedurewasasf
ol
l
ows:To
ve Al
t
oi
ds® were
det
ermi
ne t
he gl
asst
ransi
t
i
on t
emperat
ure, Tg, Fi
humi
di
f
i
ed at1 1 , 3 3 , 4 3 , 5 3 and 7 5 % RH f
or3 days.Att
hi
spoi
nt
t
he surf
ace ofeach wasscrapped of
fi
nt
oa beaker.Then, 1 0 -1 2
mg waswei
ghed i
nt
ot
he al
umi
num pans, whi
ch were t
hen cri
mped
t
o seal
.The panswere t
hen i
nt
roduced i
nt
ot
he i
nst
rument (
Perki
n
El
merDSC-7 )whi
ch wasrun f
rom -4 0 C t
o ~ 1 5 0 C wi
t
ha
mi
nut
e.The dat
a were st
ored i
nt
o an
t
emperat
ure ri
se at1 0 °C/
he
Excelf
i
l
e.The program aut
omat
i
cal
l
ydet
ermi
nest
he Tg and t
he onset
, mi
dpoi
ntand
mel
tt
emperat
ure f
oreach sampl
e.ForTg, t
endpoi
ntare aut
omat
i
cal
l
ydet
ermi
ned and f
ormel
tt
he peaki
s
recorded.
The relation between glass transition temperature and RH for sugar
candy
Tg onset
Tg end
Tg half
50.0
40.0
30.0
20.0
10.0
0.0
-10.0
-20.0
-30.0
0
10
20
30
40
50
60
70
80
RH (%)
The relation between melting temperature and RH for sugar candy
Ref
erences
140
120
100
80
60
0
10
20
30
40
RH (%)
50
The above f
i
gure and observat
i
onssummari
zest
he sensoryt
act
i
l
eresul
t
s
combi
ned wi
t
h t
heTg curve.Asseen athumi
di
t
esbel
ow t
he Tgend
poi
nt(
onl
y3 t
estcondi
t
i
ons)t
he Al
t
oi
ds® remai
ned i
n ast
abl
el
oose st
at
e.
Above t
hatt
heybecame st
i
ckyand at5 5 and6 5 °C t
hey“mel
t
ed”(
f
l
ow)t
o
f
orm a sol
i
d hardmasswhen cool
ed.Thust
heTgcurve wasa good
predi
ct
i
ve t
oolf
orst
i
ckyonset.The resul
t
soft
hi
sst
udywhere Al
t
oi
d®
hard candi
eswere st
ored open and unopenedatdi
f
f
erentt
emperat
urehumi
di
t
ycondi
t
i
onsshowed t
hatbot
ht
emperat
ure andhumi
di
t
yabuse
above t
hegl
asst
ransi
t
i
on l
i
ne f
ort
he candyresul
t
ed i
n sl
i
ghtt
o ext
reme
st
i
cki
nesssupport
i
ng t
he hypot
hesi
s.Theresul
t
ssuggestt
hatt
emperat
ure
hasa great
eref
f
ect
.
60
70
80
Bell, L. and Labuza, T.P. Moisture Sorption: Second Edition. St. Paul:
American Association Cereal Chemists, 2000.
Labuza, T.P. and P. S. Labuza. “Influence of Temperature and Relative
Humidity on the Physical States of Cotton Candy.” Journal of Food
Processing Preservation. 2004: 28: 274-287.
McLaren, C. and others. “Heat Stress From Enclosed Vehicles:
Moderate Ambient Temperatures Cause Significant Temperature Rise in
Enclosed Vehicles.” Pediatrics. 2005: 116: e109-e112.