Hurdle Technology for Functional Drinks: pH, Water Activity, Preservatives and Heat (2026)
PhD (Food Science) · Director of New Product Development, Food Research Lab
✓ Technically reviewed by FRL Editorial · Last reviewed: 5 November 2026 · Next review: May 2027
5 November 2026
Last checked
5 November 2026
Reading time
10 min
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12
- Hurdle technology combines mild controls (pH, water activity, preservatives, heat) instead of one harsh one.
- pH 4.6 is the US line: low-acid foods acidified to 4.6 or below fall under 21 CFR 114; above 4.6 in a sealed pack, 21 CFR 113.
- Acid alone can fail: Alicyclobacillus grows at pH 2.5 to 6.0.
- Preservatives can replace heat only against organisms of non-health significance in acidified foods.
- Benzoate plus vitamin C can form trace benzene, so test preservative systems with the actives in.
What is hurdle technology for functional drinks?
Hurdle technology is the deliberate combination of several preservation factors, or hurdles, so that together they keep a food microbially stable and safe. The classic hurdles are temperature, water activity (aw), acidity (pH), redox potential, competitive microorganisms and preservatives.[1] Because the factors are combined, each can be used at a less severe level, which helps protect nutritional and sensory quality; reviews credit the approach with making many perishable foods stable at ambient temperature.[2]
Leistner, who developed the concept, describes how hurdles disturb the internal balance (homeostasis) of microorganisms. Hurdles that hit different targets in the cell at the same time work better than one large hurdle, which he calls multitarget preservation.[1] For a functional drink this matters because the actives, such as vitamins, polyphenols, botanicals or proteins, are often the first casualties of a harsh single treatment.
Why one control is rarely enough
A single control has to be strong, and strong controls cost quality. Acidity is the standard example: Alicyclobacillus acidoterrestris, a heat-resistant, spore-forming spoilage bacterium, grows at pH 2.5 to 6.0 and is a known spoiler of acidic juices such as apple juice.[7] A low pH alone will not stop it, so an acidic drink needs a second hurdle, and the process has to be designed with that organism in mind.
The key hurdles in a shelf-stable functional drink
pH and acidity
pH is the first lever in most drinks, and in the US it also decides which rules apply. Under 21 CFR 114, acid foods have a natural pH of 4.6 or below, while acidified foods are low-acid foods with added acid or acid food that reach a finished equilibrium pH of 4.6 or below and have a water activity above 0.85.[3] Where the finished equilibrium pH is above 4.0, it must be measured with a potentiometric (pH meter) method.[3] Acidity also makes some microbes more sensitive to other treatments: one juice study used a lower pH specifically to make Saccharomyces cerevisiae more sensitive to pulsed electric fields.[7]
Water activity (aw)
Ready-to-drink beverages almost always have a water activity well above 0.85, so aw is rarely the main hurdle in the bottle. It matters more in syrups, concentrates, shots with high solids and powders. It also sets the regulatory scope: both the acidified-food and low-acid-food definitions apply to foods with aw above 0.85.[3][5] Measure pH and water activity together on the finished formula rather than relying on ingredient specifications.
Preservatives
Preservatives such as sorbates and benzoates add protection without heat. Sorbic acid and potassium sorbate are generally recognized as safe (GRAS) when used in line with good manufacturing practice.[9] Sodium benzoate is GRAS as an antimicrobial at levels not exceeding good manufacturing practice, and FDA notes that current usage results in a maximum of 0.1% in food.[10] Any chemical preservative must be declared on the label by its common name together with its function, for example “preservative”.[11]
Preservatives interact with the rest of the formula. Benzene can form at very low (parts-per-billion) levels in some beverages that contain both benzoate salts and ascorbic acid or erythorbic acid, and heat and light can promote it.[12] That is a direct concern for vitamin C-fortified functional drinks, so test benzoate systems with the full active load, or choose a different second hurdle. Natural antimicrobials are also being studied: in one clear apple juice study, mild heat (54 °C for 10 minutes) or pulsed electric fields were combined with essential oil components (carvacrol, citral, limonene) against spoilage yeasts and Leuconostoc bacteria.[7]
Heat and non-thermal hurdles
Heat remains the backbone of most shelf-stable drinks, and it has a cost. In one study, pasteurizing tropical fruit juice blends at 85 °C for 30 seconds left total polyphenols and antioxidant activity unchanged but reduced ascorbic acid by 7%.[7] The goal is the mildest heat that still delivers the required lethality. Non-thermal steps can add to or partly replace heat: in apple juice, pressure pretreatment at 600 MPa for 15 minutes followed by 60 minutes of power ultrasound gave a 4.2-log reduction of Alicyclobacillus spores.[7] Treatment times like these are laboratory conditions, not a commercial process. Redox potential and competitive microflora are recognized hurdles,[1] but they matter more in fermented and fresh products than in most clear functional drinks.
How hurdles work together
Combining hurdles is designed, not assumed. The effect depends on which targets each hurdle hits in the microorganism,[1] and on the matrix: the same mild heat step, for example, gave different reductions of E. coli O157:H7 in guava and mango juices.[7] Plant-based drinks show the same pattern. In an almond beverage, thermosonication at 45 °C for 40 minutes left no detectable yeasts, molds or aerobic mesophilic bacteria, but higher temperatures and longer times raised viscosity and could harm sensory scores, and all of the plant-beverage ultrasound work reviewed was at laboratory scale.[8]
Table 1. Common hurdles in functional drinks: what each does and where it falls short
| Hurdle | What it does | Where it falls short |
|---|---|---|
| pH and acidity | Slows or stops many microbes; 4.6 is the US regulatory line[3] | Acid-tolerant spoilers such as Alicyclobacillus and yeasts[7] |
| Water activity | Limits growth in syrups, concentrates and powders[1] | Little effect in high-aw ready-to-drink products[3] |
| Preservatives | Add protection without heat[9][10] | Must be declared on the label;[11] benzoate with ascorbic acid can form benzene[12] |
| Mild heat | Reduces microbial load[7] | Can reduce heat-sensitive actives such as vitamin C[7] |
| Non-thermal (HPP, ultrasound) | Adds lethality with less heat[7][8] | Spores are hard to kill; much of the data is lab scale[7][8] |
US rules that set the minimum hurdles
In the US, the hurdle system is not only a quality choice. The finished pH, water activity, storage and juice content decide which FDA process rules apply, and those rules set the minimum. Our functional beverage FDA regulations FAQ covers classification, labeling and claims; this section covers the process side.
Table 2. Which FDA process rule applies to a shelf-stable drink
| Drink profile | Rule | What it requires |
|---|---|---|
| Low-acid ingredients plus added acid; finished equilibrium pH 4.6 or below; aw above 0.85; not refrigerated | 21 CFR 114, acidified foods[3] | A scheduled process set by a qualified person; pH control and records; facility registration and process filing with FDA[3][4] |
| pH above 4.6 and aw above 0.85, in a hermetically sealed container (for example a neutral plant-based drink) | 21 CFR 113, low-acid foods[5] | A thermal scheduled process set by qualified persons, including for aseptic processing and packaging[5] |
| Contains juice (sold as juice or used as an ingredient) | 21 CFR 120, juice HACCP[6] | A HACCP plan with at least a 5-log reduction of the pertinent microorganism, unless an exemption applies[6] |
Three details matter for functional drinks. First, part 114 excludes carbonated beverages and foods stored, distributed and retailed under refrigeration, so a refrigerated cold-pressed shot and an ambient one with the same recipe face different rules.[3] Second, acidified foods must be thermally processed enough to destroy vegetative cells of public-health significance; permitted preservatives may replace heat only against organisms of non-health significance.[3] Third, juice processors already covered by part 113 or 114, or using a single thermal step sufficient for shelf stability, are exempt from the 5-log requirement but must keep that process in their written hazard analysis.[6] Confirm the classification of your product with a process authority before you lock the formula.
For a neutral, low-acid drink that has to be shelf-stable, the heat hurdle usually means retort or aseptic processing. Our pilot retort trials let brands test that heat step on pilot-scale batches of real product before a commercial run.
Designing a hurdle system for your beverage
For functional beverage development, the hurdle system is part of the recipe, not an add-on. Decide the storage claim and target pH first, choose a second hurdle that covers acid-tolerant spoilers, then set the lightest heat step that meets the safety requirement and keeps the actives. Our hub guide, how to formulate a functional beverage, places this step in the full development path.
Table 3. Checklist for a functional drink hurdle system
| Step | Check |
|---|---|
| 1. Storage and pack | Ambient or refrigerated; carbonated or still; hermetically sealed or not, decided first[3][5] |
| 2. pH and aw | Finished equilibrium pH and aw measured on the full formula; pH meter if pH is above 4.0[3] |
| 3. Rule | Part 114, 113 or 120 (or none) confirmed with a process authority[3][5][6] |
| 4. Second hurdle | Preservative, aw or mild heat chosen to cover acid-tolerant spoilers;[7] benzoate checked against ascorbic acid[12] |
| 5. Heat | Mildest step that meets the scheduled process or lethality target, with active retention measured[7] |
| 6. Validation | Challenge and stability testing of the finished drink in the final pack and storage conditions |
| 7. Records and label | Scheduled process, pH records and filings kept;[3][4] preservatives declared with their function[11] |
Formulator’s note: each hurdle can pass on its own and the system can still fail. Run challenge and stability tests on the finished formula with the actives in it. Our beverage stability testing guide sets out the physical, chemical and microbial tests, and the Slimsy squash recall analysis shows what spoilage yeast can do when the hurdles are not enough.
Worked example: a heat-stable plant beverage
Starch-rich plant drinks show the trade-offs clearly. Heat is needed for safety, but it can gelatinize starch and thicken the drink, as our article on plant-based beverage stability after heat treatment explains. FRL’s own Inside the Lab oat milk trial aimed for a ready-to-drink oat milk with no added sugar and no preservatives, which leaves heat and process design to carry the preservation load; the lab trials went well and further stability trials were planned. Our heat-stable plant beverage worked example walks through that kind of product step by step.
Conclusion
Hurdle technology replaces one harsh control with several gentle ones, which suits functional drinks that carry heat-sensitive actives. In the US, the finished pH, water activity, storage and juice content also decide which FDA process rules apply, so settle those first. Then add a second hurdle for acid-tolerant spoilers, keep heat as light as the scheduled process allows, check how the preservative interacts with the actives, and confirm the whole system with challenge and stability testing before launch. For budgeting that work, see our functional beverage development cost guide.
For brands & formulators
Food Research Lab’s beverage formulation service helps US brands design the hurdle system for a shelf-stable functional drink: target pH and acidulant, preservative choice and label impact, and the lightest heat or non-thermal step that keeps the actives. For low-acid drinks we can run pilot retort trials, and our shelf-life study service covers stability and challenge testing, which we run or arrange through accredited partner laboratories.
Send us your concept, target claims and storage plan through our contact page.
In this series
This guide is part of FRL’s functional beverage development series for the US market.
- Functional beverage development cost guide: budget and timeline by development stage.
- How to formulate a functional beverage: the hub guide, from target profile to shelf-stable batch.
- Hurdle technology for functional drinks (you are here): pH, water activity, preservatives and heat, and the FDA rules behind them.
- Heat-stable plant beverage worked example: one product taken through formulation and processing.
- Functional beverage FDA regulations FAQ: US classification, labeling and process questions answered.
- Beverage formulation service: work with FRL on your drink.
- ✓Decide the storage claim and pack first: ambient or refrigerated, carbonated or still.
- ✓Measure finished equilibrium pH and water activity on the full formula, then confirm whether 21 CFR 113, 114 or 120 applies.
- ✓Add a second hurdle for acid-tolerant spoilers and check benzoate against any added vitamin C.
- ✓Set the mildest heat step that meets the scheduled process, and measure active retention.
- ✓Validate the combination with challenge and stability testing in the final pack, for example through our shelf-life study service.
What is hurdle technology in functional drinks?
Hurdle technology combines several preservation factors, such as pH, water activity, preservatives and mild heat, so that together they stop microbial growth even though each is used at a gentler level.[1][2] In functional drinks it helps keep a product safe and stable while protecting heat-sensitive actives such as vitamins and polyphenols.
Is a functional drink with a pH of 4.6 or below an acidified food?
Only if it is a low-acid food made acidic by adding acid or acid food, with water activity above 0.85.[3] Drinks with a natural pH of 4.6 or below are acid foods. Carbonated beverages and foods kept under refrigeration through distribution and retail are excluded from the acidified-food rule in 21 CFR 114.[3]
Can preservatives replace heat in a shelf-stable functional drink?
Only partly. Under 21 CFR 114, acidified foods must be thermally processed enough to destroy vegetative cells of microorganisms of public-health significance.[3] Permitted preservatives may be used instead of heat only against organisms of non-health significance. Preservatives therefore usually reduce the heat a drink needs rather than removing the heat step.
Why can an acidic functional drink still spoil?
Some spoilers tolerate acid. Alicyclobacillus acidoterrestris, a heat-resistant spore-former, grows from pH 2.5 to 6.0 and spoils acidic juices, and spoilage yeasts such as Saccharomyces cerevisiae withstand low pH and preservatives better than many bacteria.[7] That is why a low pH is usually paired with a second hurdle, such as a preservative or a validated heat step.
Is hurdle technology better than heavy pasteurization for functional drinks?
It can be, because several mild hurdles can reach the same stability with less heat, which protects flavor, color and actives; one study found 85 °C for 30 seconds cut vitamin C in tropical juice by 7%.[7] The right combination depends on the drink and must be validated by challenge and stability testing.
Can I use sodium benzoate in a vitamin C functional drink?
With care. Sodium benzoate is GRAS at levels within good manufacturing practice, with current usage up to 0.1%.[10] FDA reports that benzene can form at very low levels in drinks containing benzoate salts and ascorbic acid, especially with heat and light.[12] Test the full formula in its final pack, or choose another preservative.
- Leistner, L. (2000). Basic aspects of food preservation by hurdle technology. International Journal of Food Microbiology, 55(1–3), 181–186. https://doi.org/10.1016/S0168-1605(00)00161-6 (cited for the hurdle concept, the main hurdles (temperature, aw, pH, redox potential, competitive flora, preservatives), microbial homeostasis and multitarget preservation).
- Abdullahi, N., & Dandago, M. A. (2021). Hurdle technology: Principles and recent applications in foods. Indonesian Food and Nutrition Progress, 17(1), 6–11. https://doi.org/10.22146/ifnp.52552 (cited for combining preservation factors at less severe levels to protect nutritional and sensory quality, and many perishable foods now being ambient-stable).
- U.S. Food and Drug Administration. (2026). 21 CFR Part 114: Acidified foods. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-114 (cited for §114.3 definitions of acid, acidified and low-acid foods, the pH 4.6 and aw 0.85 thresholds and the exclusions (carbonated beverages, refrigerated foods); §114.80 thermal processing, preservatives in lieu of heat only for organisms of non-health significance, potentiometric pH above 4.0; §114.83 scheduled process by a qualified person).
- U.S. Food and Drug Administration. (2026). 21 CFR 108.25: Acidified foods (emergency permit control; registration and process filing). Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-108/subpart-B/section-108.25 (cited for registration of acidified-food processors and filing of scheduled processes with FDA).
- U.S. Food and Drug Administration. (2026). 21 CFR Part 113: Thermally processed low-acid foods packaged in hermetically sealed containers. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-113 (cited for the low-acid food definition (pH above 4.6, aw above 0.85), aseptic processing and packaging, and scheduled processes set by qualified persons (§113.83)).
- U.S. Food and Drug Administration. (2026). 21 CFR Part 120: Hazard Analysis and Critical Control Point (HACCP) systems [juice]. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-120 (cited for §120.1 applicability to juice sold as such or used as a beverage ingredient; §120.24 5-log reduction and the exemptions for part 113/114 processors and single thermal shelf-stability steps).
- Putnik, P., Pavlić, B., Šojić, B., Zavadlav, S., Žuntar, I., Kao, L., Kitonić, D., & Bursać Kovačević, D. (2020). Innovative hurdle technologies for the preservation of functional fruit juices. Foods, 9(6), 699. https://doi.org/10.3390/foods9060699 (cited for Alicyclobacillus acidoterrestris growth at pH 2.5–6.0; 7% ascorbic acid loss after pasteurization at 85 °C for 30 s; 4.2-log spore reduction with 600 MPa for 15 min then 60 min ultrasound; mild heat or PEF with essential oil components in apple juice; pH used to sensitise yeast to PEF; matrix-dependent mild-heat reductions in guava and mango juices).
- Sotelo-Lara, D. M., Amador-Espejo, G. G., Álvarez-Araiza, D. F., Cordero-Rivera, A. K., Millán-Quintero, K. G., Campos-Vega, R., & Velázquez-Estrada, R. M. (2024). Ultrasound and thermosonication as promising technologies for processing plant-based beverages: A review. Food Technology and Biotechnology, 62(4), 538–552. https://doi.org/10.17113/ftb.62.04.24.8624 (cited for thermosonication of an almond beverage at 45 °C for 40 min (no detectable yeasts, molds or aerobic mesophiles; viscosity and sensory effects at higher temperature and time) and the laboratory scale of the work reviewed).
- U.S. Food and Drug Administration. (2026). 21 CFR 182.3640 Potassium sorbate; 182.3089 Sorbic acid. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-182/subpart-D/section-182.3640 (cited for GRAS status of sorbic acid and potassium sorbate under good manufacturing practice).
- U.S. Food and Drug Administration. (2026). 21 CFR 184.1733 Sodium benzoate. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-184/subpart-B/section-184.1733 (cited for GRAS antimicrobial use at levels not exceeding good manufacturing practice; current usage maximum 0.1% in food).
- U.S. Food and Drug Administration. (2026). 21 CFR 101.22: Foods; labeling of spices, flavorings, colorings and chemical preservatives. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-101/subpart-B/section-101.22 (cited for §101.22(j): declaration of a chemical preservative by name and function).
- U.S. Food and Drug Administration. (2022). Questions and answers on the occurrence of benzene in soft drinks and other beverages. https://www.fda.gov/food/process-contaminants-food/questions-and-answers-occurrence-benzene-soft-drinks-and-other-beverages (cited for benzene formation at ppb levels in beverages with benzoate salts and ascorbic or erythorbic acid, promoted by heat and light).
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