candy research
Preliminary Comparative Study on the Effect of Aqueous White Colour Slurry and Direct White Colour Powder Addition on the Stability of Traditional Handmade Hard Candy
Study Organiser: Jian Ma
Study Participants: Brenton Baddeley, Edward Wang
Research Site: Designer Candy, Melbourne, Australia
Study Period: 12 August 2026 – 30 August 2026
Abstract
Objective:
To investigate whether the method of adding white food colour—either as a freshly prepared aqueous slurry or by direct addition of dry powder—affects the stability of traditional handmade hard candy under accelerated hot and humid conditions, and to preliminarily assess the potential influence of the additional water introduced during colour preparation.
Methods:
Batches B2 and B10 from the same accelerated stability study were selected for comparison. Both batches contained 3 kg of sugar and 750 g of glucose syrup, corresponding to a sugar-to-glucose syrup ratio of 10:2.5. The same type and quantity of white colour, as well as the same other colours, were used in both batches. In B2, the white colour was freshly prepared with water at the standard production ratio to form a slurry before addition, and the final cooking temperature was 160°C. In B10, the same quantity of white colour was added directly as dry powder without preparation as an aqueous slurry, and the final cooking temperature was 158°C.
All samples were produced and packed on the same day. A 100 g sample 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 used to provide a high-humidity environment of RH ≥60%. Appearance (A) and Mouthfeel (M) were assessed during the study. A batch was considered to have reached its stability endpoint when either A or M first became unacceptable.
Results:
B2, in which the white colour was added as an aqueous slurry, reached the failure endpoint on Day 6. B10, in which the same white colour was added directly as dry powder, reached the failure endpoint on Day 11. Under these accelerated conditions, the observed stability period of the dry-powder batch was 5 days longer, representing an increase of approximately 83% compared with B2.
Conclusion:
Under the conditions of this preliminary comparison, direct addition of white colour powder was associated with a substantially longer accelerated stability period than the conventional aqueous white colour slurry method. Although the final cooking temperatures differed by 2°C, B2 was cooked at the higher temperature, which would theoretically favour greater moisture removal, yet it still reached the failure endpoint earlier. These findings support the hypothesis that additional water introduced during colour slurry preparation may adversely affect the stability of traditional handmade hard candy. A strictly temperature-matched single-variable comparison would be required to confirm this effect.
Keywords: traditional handmade hard candy; white food colour; colour slurry; moisture; dry powder; hygroscopicity; accelerated stability
1. Introduction and Objective
In traditional handmade hard candy production, some food colours are prepared with water at a standard ratio before use. This produces a colour slurry that facilitates dispersion and practical handling during candy production. At Designer Candy, the white colour slurry is prepared fresh for each production batch according to a standard formulation.
Hard candy production, however, relies on high-temperature cooking to remove water from the sugar mass. Preparing a colour slurry with water subsequently introduces a small additional quantity of water into the candy mass. Although this quantity is relatively small compared with the total batch weight, it is reasonable to investigate whether such additional moisture may influence subsequent moisture absorption, softening, sticking, caking or mouthfeel stability.
During the previous accelerated stability study examining glucose syrup ratios and final cooking temperatures, B2 and B10 were produced using the same sugar-to-glucose syrup ratio and the same type and quantity of white colour, but with different methods of white colour addition.
The present study therefore compares B2 and B10 as a preliminary investigation of the effect of standard aqueous white colour slurry preparation versus direct addition of dry white colour powder on the accelerated stability of traditional handmade hard candy.
2. Materials and Methods
2.1 Study Personnel
The study was organised and coordinated by Jian Ma, with Brenton Baddeley and Edward Wang participating in sample production, observation and assessment.
2.2 Materials
The sugar used in the experiment was obtained from Costco, and the glucose syrup was supplied by Manildra. The two batches were produced using the same batches of principal raw materials, including glucose syrup from the same lot.
The same white food colour and the same quantity of white colour were used in B2 and B10. Other colours and production materials were also kept the same between the two batches.
For normal production, the white colour slurry was freshly prepared with water according to the established standard ratio before use. In B10, this slurry-preparation step was omitted, and the same quantity of white colour was added directly in dry-powder form.
2.3 Comparative Design
| Parameter | B2 – Aqueous Slurry | B10 – Dry Powder |
|---|---|---|
| Sugar | 3 kg | 3 kg |
| Glucose syrup | 750 g | 750 g |
| Sugar : glucose syrup | 10:2.5 | 10:2.5 |
| White colour | Same | Same |
| Quantity of white colour | Same | Same |
| Other colours | Same | Same |
| White colour addition | Freshly prepared aqueous slurry at standard ratio | Direct dry-powder addition |
| Final cooking temperature | 160°C | 158°C |
| Production date | Same | Same |
| Accelerated environment | 30°C, RH ≥60% | 30°C, RH ≥60% |
The principal difference of interest was therefore the method of white colour addition. However, there was also a 2°C difference in final cooking temperature between the two batches. This difference was taken into account when interpreting the results, and the comparison was not treated as a strictly controlled single-variable experiment.
2.4 Accelerated Stability Study
The samples were produced and packed on 12 August 2026, and accelerated testing commenced on the same day.
A 100 g sample of candy from each batch was placed in a bag that was left completely open, allowing direct exposure of the candy to the hot and humid test environment.
Samples were stored in a commercial food holding cabinet set at a constant temperature of 30°C. A water tray was placed inside the cabinet to provide moisture through natural evaporation and maintain a high-humidity environment of RH ≥60%.
The first assessment was conducted on 13 August 2026, approximately 24 hours after the samples were placed in the cabinet, and was designated Day 1. The study continued until 30 August 2026.
2.5 Assessment Criteria and Failure Endpoint
Two parameters were used to assess stability:
A – Appearance: assessment of whether the candy pieces showed deformation, sticking or caking.
M – Mouthfeel: assessment of hardness, brittleness, softening, tooth-stickiness and changes in flavour.
If either A or M became unacceptable, the batch was considered to have reached its stability endpoint and was withdrawn from further assessment.
3. Results
The two batches showed clearly different stability periods under the same open-bag, hot and humid accelerated conditions.
| Batch | White Colour Addition | Final Cooking Temperature | Failure Endpoint |
|---|---|---|---|
| B2 | Aqueous white colour slurry | 160°C | Day 6 |
| B10 | Direct dry white colour powder | 158°C | Day 11 |
B2, produced using the conventional aqueous white colour slurry, reached the failure endpoint on Day 6, whereas B10, produced by direct addition of dry white colour powder, remained acceptable until Day 11.
The observed accelerated stability period of B10 was therefore 5 days longer than that of B2.
Relative to the 6-day stability period of B2:
(11 − 6) ÷ 6 × 100% ≈ 83%
Thus, under the conditions of this study, the observed accelerated stability period of the dry-powder batch was approximately 1.83 times that of the aqueous-slurry batch.
4. Discussion
4.1 Effect of White Colour Addition Method
B2 and B10 were produced using the same sugar-to-glucose syrup ratio and the same type and quantity of white colour. The principal processing difference of interest was that B2 used the standard aqueous white colour slurry, whereas B10 used direct addition of the white colour in dry-powder form.
B10 reached its stability endpoint on Day 11, compared with Day 6 for B2, giving a difference of 5 days.
This observation suggests that, although the quantity of water used to prepare the white colour slurry represents only a small proportion of the total candy mass, the additional water introduced during colour preparation may influence the subsequent stability of traditional handmade hard candy under hot and humid conditions.
4.2 Influence of the Difference in Final Cooking Temperature
An important factor in interpreting this comparison is the 2°C difference in final cooking temperature.
B2 was cooked to 160°C, whereas B10 was cooked to 158°C. From a practical candy-processing perspective, the higher final cooking temperature of B2 would be expected to favour greater moisture evaporation and could therefore partially compensate for the additional water introduced through preparation of the aqueous white colour slurry.
If higher final cooking temperature were the dominant factor determining the difference between these two batches, B2 would not be expected to be at an obvious disadvantage.
The experimental result, however, was the opposite: B2 reached its failure endpoint on Day 6, whereas B10, despite being cooked 2°C lower, remained acceptable until Day 11.
The longer stability of B10 therefore cannot simply be explained by a higher cooking temperature or greater moisture removal during cooking. Instead, the observation provides additional support for the possibility that eliminating the water introduced during preparation of the white colour slurry may have contributed to the improved stability of B10.
Nevertheless, because the final cooking temperatures were not identical, the entire 5-day difference cannot be attributed solely to the water introduced through the colour slurry on the basis of the present study.
4.3 Nature and Limitations of the Study
This study was conducted under practical handmade candy production conditions rather than as a laboratory-based, fully controlled single-factor experiment.
Its strength is that both batches were produced using the same principal raw materials, on the same production day, and were subsequently exposed to the same accelerated environment and evaluated using the same acceptance criteria.
However, B2 and B10 differed by 2°C in final cooking temperature, and the present comparison consisted of one aqueous-slurry batch and one dry-powder batch without independent replicate batches produced under completely identical processing conditions.
The findings should therefore be regarded as a preliminary comparative observation rather than definitive proof of a causal relationship.
5. Conclusion
Under open-bag accelerated conditions of 30°C and RH ≥60%, B2, produced using the conventional aqueous white colour slurry, reached the failure endpoint on Day 6, whereas B10, produced using the same white colour and quantity but added directly as dry powder, reached the failure endpoint on Day 11.
The dry-powder batch therefore showed an accelerated stability period 5 days longer, corresponding to an approximately 83% increase compared with the aqueous-slurry batch.
Notably, B10 had a final cooking temperature of 158°C, which was 2°C lower than the 160°C used for B2. Although the higher cooking temperature of B2 would theoretically provide more favourable conditions for moisture evaporation, its observed stability period remained substantially shorter.
The findings therefore support the hypothesis that:
Additional water introduced during preparation of an aqueous white colour slurry may adversely affect the stability of traditional handmade hard candy under hot and humid conditions, while direct addition of dry white colour powder may improve product stability by reducing the introduction of external moisture.
Because the two batches differed by 2°C in final cooking temperature and no strictly temperature-matched replicate comparison was performed, this finding should be regarded as preliminary process evidence rather than definitive proof of the effect of water introduced through colour slurry preparation.
A future controlled comparison using the same final cooking temperature, formulation, colour quantity, raw materials and production conditions, with the white colour addition method as the only variable, would provide a stronger test of the effect observed in this study.
The original experimental design documents the formulation, cooking temperatures and dry-powder condition for B2 and B10, while the accelerated stability records document their observations within the same study.