For food processing suppliers or system integrators, the safety of cooling devices directly impacts your compliance and brand risk. Glycol chillers are one of the most widely used cooling devices, so one concern is: Is a glycol chiller safe for food? The answer is Yes, but under specific conditions. Now, let’s explore this topic further.
What Is a Glycol Chiller?
The glycol chiller is an efficient industrial cooling system. It uses glycol (usually propylene glycol) and water as a medium to remove heat from your production process.
A glycol chiller is usually combined with a compressor, an evaporator, a condenser, and a water pump. It operates through a refrigeration cycle within these components. First, it cools this mixture of glycol and water to an extremely low temperature. Next, the cold liquid flows through pipes to the equipment that needs cooling, absorbs heat, and warms up. Finally, the warmed liquid flows back to the water chiller to be cooled again.
Is Glycol Itself Safe for Food?
Glycol plays a critical role in chiller systems because it allows the system to operate below zero degrees without freezing. Without it, the pure water (as a medium) will freeze at 0 °C and burst the pipes. Besides, high-quality glycol contains corrosion inhibitors, which can lubricate the pump body and prevent rusting.
Therefore, an important part of assessing the safety of a glycol chiller is to judge the safety of glycol itself.
Types of Glycol
Whether a glycol is safe for food depends on its type. Generally, glycols can be divided into two types: propylene glycol and ethylene glycol.
Propylene Glycol
Propylene glycol is the only glycol type permitted in the food and beverage industry. It has been classified by the US FDA as GRAS (Generally Recognized as Safe).
For food-grade propylene glycol, even though there is a small amount that leaks and mixes with food during the chiller operation, it usually does not harm human health (but contamination is still unacceptable in most regulated food processes).
Ethylene Glycol
Ethylene glycol is commonly used as an antifreeze in cars and in industrial cooling systems. It is forbidden to apply to any food processing due to its toxicity! Even a very small amount ingested can cause damage to the central nervous system, kidney failure, and even death in humans.
When Is a Glycol Chiller Safe for Food Applications?
When choosing a glycol chiller that is safe for food application, you have to consider the following factors.
Use Correct Cooling Medium
You only need to purchase USP-grade (pharmaceutical-grade) or food-grade propylene glycol as the heat-transfer medium.
Never use industrial antifreeze containing ethylene glycol in the food industry.
Use Food-Grade Material
The side of the heat exchanger (plate type or shell-and-tube type) that comes into contact with food must be made of food-grade stainless steel, such as 304 or 316. It is resistant to corrosion and is easy to clean, and it does not react with acidic foods.
You should also use a food-grade lubricant in the compressor and use a lead-free and cadmium-free coating, ensuring that everything in contact with your food is safe.
Apply Closed-Loop System
A food processing chiller that applies a closed-loop system can largely improve the safety of your glycol chiller.
No Direct Contact
In the closed-loop system, the cooling medium is always sealed and circulates within the pipes, pumps, and heat exchangers. As long as the pipeline is not damaged, the glycol cannot contact your food.
Prevent External Contamination
An open-circuit system (such as a cooling tower) is exposed to the air and is prone to being mixed with dust, insects, leaves, breeding legionella bacteria, etc. In comparison, a closed-loop system is sealed, so external impurities cannot enter the cooling cycle. This prevents the cooling medium from becoming a breeding ground for bacteria.
Maintain Chemical Stability
Glycol in the closed-loop system is less prone to oxidation because it is not exposed to air. This can protect the pipes from corrosion, and the water does not evaporate, ensuring the long-term stability of anti-freezing protection.
Equip Physical Isolation Mechanism
It’s safer for you to employ an “indirect cooling” design to ensure that there are at least two physical barriers between the cooling fluid and your food. Here are two kinds of physical isolation configurations.
Jacketed Vessels
By using a jacketed vessel design, you can control glycol flows in the outer wall jacket of the fermentation tank or mixing tank, not in direct contact with the food inside.
Plate and Frame Heat Exchangers (PHEs)
You can use high-quality stainless steel plates as a secondary heat exchanger to separate the food fluid (such as milk or juice) from the glycol fluid.
Complying with Specific Industry Standards and Regulations
There are some regulations that strictly define a safe glycol chiller.
- The glycol and system lubricants used in your chiller must comply with the regulations for food contact materials, such as FDA/NSF.
- It is necessary for you to regularly conduct pH value tests and maintain corrosion inhibitors (to prevent acidic corrosion from allowing heavy metals to seep into the food) and pressure tests (to prevent cracks from causing large-scale leaks).
- You need to add food-grade dyes into the coolant so that workers can immediately identify product contamination by visual inspection in case of a leak.
What Can Lead to the Unsafety of a Glycol Chiller in Food Applications?
Except for the solutions proposed above to ensure that your glycol chiller is safe for food, some factors can also compromise the safety.
Cross-Contamination
- Heat Exchanger Perforation
Long-term operation can lead to wear, pressure shock, or acidic corrosion, causing micro-cracks in plate heat exchangers or jacketed tanks. The chiller is always operating under certain pressures, so the glycol may be forced into the food side from these cracks.
- Sealing Components’ Aging
If the sealing rings of pumps and valves are not made of food-grade materials or fail due to aging, they can also lead to leakage.
Solution
- To prevent physical barrier failure, you can apply the double-wall heat exchangers (which we have proposed above).
- Regularly conduct high-pressure tests on the glycol circuit and the food circuit separately, observing whether there are invisible micro-cracks.
- Always ensure that the pressure on the food side is higher than that on the glycol side. In this way, even if the barrier is damaged, the food will flow into the glycol pipeline.
- Install a sensor at the outlet of your food pipeline to monitor conductivity. If there’s a leakage, the conductivity will change, and the sensor will alarm.
Microbial Growth
- Insufficient Glycol Concentration
If the concentration of glycol drops below 25%, it not only loses its antifreeze effect but also promotes microbial growth. If such contaminated liquid leaks, it will bring a huge hygiene risk to your production environment.
- Liquid Accumulation
If the pipes are not designed properly and there is liquid accumulation left in dead zones, bacteria can easily grow.
Solution
- Always maintain a high concentration of glycol above 25%. We recommend that you use a refractometer to inspect the concentration every month.
- Use food-grade additives containing disinfectants.
- Let your chiller operate for a while (about 15 – 30 minutes) even during nonproduction seasons. This can prevent static liquid deposition and bacterial proliferation.
- Use high-purity water to prepare the coolant.
- Clean your chiller entirely once a year. That includes removing internal deposits with food-grade pipe cleaning agents and replacing a brand-new propylene glycol solution.
FAQ
How to Calculate the Cooling Capacity of a Glycol Chiller?
To calculate the cooling capacity of a glycol chiller, you need to measure the data of material quality (m), specific heat (cₚ), temperature variation (ΔT), and cooling time (t). Then you can figure out the cooling capacity with the formula: Q = m × cₚ × ΔT/t.
In practice, you have to take additional heat load (pump heat, environmental loss, heat release reactions, etc.) into consideration, so 20%-25% redundancy should be added.
How to Deal With a Glycol Chiller Leakage?
If you find there is a leakage, you need to shut off your chiller pump immediately and cut off the valves.
If the leakage enters the food, you need to extract samples for conductivity, pH value, or chromatography analysis to confirm the degree of contamination. Food products contaminated with propylene glycol usually must be abandoned.
If the leakage is external to the ground, you need to clean it with absorbents. Remember to put on rubber gloves and goggles to prevent slipping. Finally, you can inspect to find and repair the leaks.
How to Determine the Concentration of Glycol Required by the System?
Too low a concentration of glycol can freeze your pipeline, and too high a concentration can reduce the cooling effect. In the food system, the concentration should range from 25% to 50%. Usually, the most common glycol concentration applied in food applications is about 30%.
Ethylene glycol vs. Propylene Glycol Chillers: What’s the Difference?
Ethylene glycol is toxic and is forbidden to be applied to food processing, pharmaceuticals, or any system that may come into contact with water. It has higher heat transfer efficiency and lower viscosity. Its production cost is lower. So an ethylene glycol chiller is an industrial glycol chiller that is always used in industrial manufacturing, heating, HVAC, skating rinks, etc.
Propylene glycol is food-grade, with higher viscosity and lower heat transfer efficiency. A propylene glycol chiller always has a higher price because of its high safety features, and it can be applied in environments with a risk of food contact.
What are the Advantages of Glycol Chillers Applied in Food Applications?
Compared with ordinary water-cooling systems or direct-cooling equipment, glycol chillers have lots of advantages. It can cool your food below zero degrees without freezing. The inhibitors in glycol can protect the interior of the system from rusting. And with the highly sensitive temperature control system, the glycol chiller can control the temperature difference within a very small range.
Final Thoughts
From the content above, you can now understand that the safety of a glycol chiller is determined by lots of factors. It is not just about the fluid but about reliability, sealing, and compliance. Chillerone has profound experience in manufacturing food-grade glycol chillers with stable cooling performance. Contact us, and you can get a cooling solution tailored to your food application!
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