Study Organiser: Jian Ma
Study Participants: Brenton Baddeley, Edward Wang
Study Period: 12 August 2026 – 30 August 2026

Research Site: Designer Candy, Melbourne, Australia

Abstract

Objective:
This study investigated the effects of the sugar-to-glucose syrup ratio and final cooking temperature on the appearance, mouthfeel and stability of traditional handmade hard candy under accelerated hot and humid conditions, with the aim of identifying suitable processing parameters for improved product stability.

Methods:
Using raw materials from the same batches, nine experimental batches were prepared using three sugar-to-glucose syrup ratios (10:2.5, 10:3.0 and 10:3.5) and three final cooking temperatures (155°C, 160°C and 165°C). All samples were produced and packed on the same day. For accelerated stability testing, 100 g of candy from each batch was placed in an open bag and stored in a commercial food holding cabinet maintained at 30°C. A water tray was placed inside the cabinet to maintain a relative humidity of at least 60%. Assessment commenced approximately 24 hours after storage and continued until 30 August 2026. Appearance (A) and Mouthfeel (M) were assessed. A batch was considered to have reached its stability endpoint and was withdrawn from further assessment when either A or M first became unacceptable. The original experimental design and assessment criteria were established before testing.

Results:
Clear differences in accelerated stability were observed among the nine processing combinations. Batch 8, produced at a sugar-to-glucose syrup ratio of 10:3.5 and a final cooking temperature of 160°C, showed the best overall stability, remaining acceptable until Day 15. Batches 5 and 6, produced at a ratio of 10:3.0 and final cooking temperatures of 160°C and 165°C respectively, were the next best-performing groups, both reaching the endpoint on Day 11. The results demonstrated that stability did not continuously improve simply by increasing either the glucose syrup proportion or the cooking temperature.

Conclusion:
Within the processing ranges investigated, a sugar-to-glucose syrup ratio of 10:3.5 combined with a final cooking temperature of 160°C provided the best accelerated stability. The study indicates that an appropriate combination of glucose syrup ratio and final cooking temperature is more important than simply increasing either parameter independently.

Keywords: handmade hard candy; glucose syrup; cooking temperature; stickiness; mouthfeel; accelerated stability; hot and humid conditions

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1. Introduction and Objective

Traditional handmade hard candy may undergo moisture absorption, softening, stickiness, deformation and changes in mouthfeel when exposed to warm and humid conditions. In addition to packaging and storage environment, the composition of the candy mass and the cooking process may directly influence product stability.

Glucose syrup is an important ingredient in traditional hard candy production, while final cooking temperature is a key processing parameter affecting the finished candy mass.

The objective of this study was therefore to evaluate the combined effects of sugar-to-glucose syrup ratio and final cooking temperature on the stability of traditional handmade hard candy.

An open-bag accelerated test under controlled warm and high-humidity conditions was used to allow differences between the processing combinations to become apparent within a relatively short period.

2. Materials and Methods

2.1 Raw Materials

The granulated sugar used in the study was purchased from Costco, and the glucose syrup was supplied by Manildra.

All experimental batches were prepared using raw materials from the same respective batches, including glucose syrup from the same production lot. Colourings and other production ingredients were also kept consistent.

All nine experimental batches were produced and packed on the same day to minimise variation associated with raw-material batches, production date and storage commencement time.

2.2 Experimental Design

Each batch contained 3 kg of sugar. Three glucose syrup levels and three final cooking temperatures were combined to form nine experimental groups.

This design allowed cooking-temperature effects to be compared at a constant glucose syrup ratio, and glucose-syrup-ratio effects to be compared at a constant cooking temperature.

2.3 Accelerated Stability Conditions

Production and packing of the experimental samples were completed on 12 August 2026, when the accelerated stability study commenced.

For each experimental batch, 100 g of candy was placed in a packaging bag. The bags were deliberately left open, allowing the candies to be directly exposed to the surrounding atmosphere and facilitating moisture uptake.

The samples were placed in a commercial temperature-controlled food holding cabinet set at 30°C. A tray containing water was placed inside the cabinet to provide continuous moisture through natural evaporation and to maintain a relative humidity of at least 60% (RH ≥60%).

The open-bag design was deliberately selected to reduce the protective influence of packaging and accelerate the development of moisture-related changes, thereby allowing differences associated with formulation and cooking conditions to become apparent.

The first assessment was performed on 13 August 2026, approximately 24 hours after the test commenced, and was designated Day 1.

After eight consecutive days of assessment, there was one day on which no assessment was conducted because no staff were present. The samples nevertheless remained continuously exposed to the accelerated test environment, and this day was therefore included in the total exposure period. Assessments subsequently resumed and the study concluded on 30 August 2026.

2.4 Assessment Criteria and Failure Endpoint

Two principal criteria were used:

A – Appearance:
Assessment of visible deformation of individual candy pieces and whether candies had begun to stick or cake together.

M – Mouthfeel:
Sensory assessment including hardness, brittleness, softening, tooth-stickiness and noticeable changes in flavour.

An acceptable result was recorded as ✓, while an unacceptable result was recorded as ×.

A strict failure criterion was applied: if either Appearance (A) or Mouthfeel (M) became unacceptable, the batch was considered to have reached its accelerated stability endpoint and was withdrawn from further assessment.

Therefore, the stability duration reported for each batch represents the day on which either A or M first became unacceptable.

3. Results

Substantial differences in stability duration were observed among the nine experimental groups under the 30°C and RH ≥60% open-bag conditions.

Table 2. Accelerated Stability Results

The best-performing group was B8 (10:3.5, 160°C), which did not reach the failure criterion until Day 15.

The next best-performing groups were B5 (10:3.0, 160°C) and B6 (10:3.0, 165°C), both of which reached the failure endpoint on Day 11.

B7 (10:3.5, 155°C) reached its endpoint on Day 10, while B9 (10:3.5, 165°C) reached its endpoint on Day 9.

At the lowest glucose syrup ratio of 10:2.5, stability was substantially shorter: B1 failed on Day 1, B2 on Day 6 and B3 on Day 7.

4. Discussion

The relationship between glucose syrup ratio, cooking temperature and accelerated stability becomes particularly clear when the results are arranged as a 3 × 3 matrix.

Table 3. Stability Endpoint by Glucose Syrup Ratio and Cooking Temperature

4.1 Effect of Glucose Syrup Ratio

At a constant cooking temperature of 160°C, increasing the glucose syrup ratio produced a clear increase in accelerated stability:

10:2.5 → 6 days
10:3.0 → 11 days
10:3.5 → 15 days

A similar effect was evident at 155°C, where the 10:2.5 and 10:3.0 groups both reached the failure criterion on Day 1, whereas the 10:3.5 group remained acceptable until Day 10.

These findings indicate that, within the formulation range investigated, a higher glucose syrup proportion generally improved resistance to deterioration under the accelerated open-bag conditions.

4.2 Effect of Final Cooking Temperature

The results also demonstrate that a higher final cooking temperature did not necessarily result in greater stability.

This was particularly evident at the 10:3.5 ratio:

155°C → 10 days
160°C → 15 days
165°C → 9 days

Increasing the final cooking temperature from 155°C to 160°C improved stability considerably. However, increasing it further to 165°C reduced the observed stability from 15 days to 9 days.

At the 10:3.0 ratio, stability increased sharply from only 1 day at 155°C to 11 days at 160°C, but increasing the temperature further to 165°C produced no additional improvement.

These observations suggest that, under the conditions of this experiment, approximately 160°C represented a more favourable cooking temperature than either 155°C or 165°C when considered across the tested formulations.

4.3 Combined Effect of Formulation and Cooking Conditions

The results indicate that neither glucose syrup ratio nor cooking temperature should be considered independently.

The best result was obtained from the specific combination of 10:3.5 glucose syrup ratio and 160°C final cooking temperature, rather than from either the highest cooking temperature or simply one parameter being maximised.

B8 remained acceptable until Day 15 compared with Day 11 for B5 at the same 160°C cooking temperature. This represents approximately a 36% longer accelerated stability period.

Similarly, at the same 10:3.5 formulation, B8 at 160°C remained acceptable for 15 days compared with 9 days for B9 at 165°C—approximately 67% longer under the accelerated conditions.

The findings therefore support the existence of an appropriate formulation–temperature combination for handmade hard candy production.

5. Conclusion

This study evaluated nine combinations of sugar-to-glucose syrup ratio and final cooking temperature under an open-bag accelerated environment of 30°C and RH ≥60%.

Accelerated stability endpoints ranged from Day 1 to Day 15, demonstrating substantial differences among the processing combinations.

The best-performing condition was:

Sugar : Glucose Syrup = 10:3.5
Final Cooking Temperature = 160°C
Accelerated Stability Endpoint = Day 15

The next best-performing conditions were 10:3.0 at 160°C and 10:3.0 at 165°C, both reaching the endpoint on Day 11.

The results also demonstrate that increasing final cooking temperature does not necessarily improve stability. At a sugar-to-glucose syrup ratio of 10:3.5, increasing the temperature from 160°C to 165°C reduced the accelerated stability endpoint from 15 days to 9 days.

Within the experimental range investigated, the combination of 10:3.5 sugar-to-glucose syrup ratio and a 160°C final cooking temperature provided the best overall accelerated stability for traditional handmade hard candy.

Because the test used deliberately open packaging under warm, high-humidity conditions, the measured number of days represents a comparative accelerated stability endpoint and should not be interpreted directly as the normal shelf life of the finished packaged product.