Viscosity is defined as the “interaction between the different molecules in a fluid – this can be also understood as friction between the molecules in the fluid” and can be measured with various types of viscometers and rheometers using the measurement of centipoise (cP). When creating produce for consumption, manufacturers need to understand the effect created by food and beverage viscosity, which can be affected by the conditions within which it’s used, and are an important consideration when determining manufacturing methods.
Examples of different food and beverage items and their approximate viscosities are noted in the below table:
| Product (at room temperature unless specified) | Viscosity (centipoise cP)
|
|---|
| Acetate glue | 1200-1400 |
| Anti-freeze | 15 |
| Baby food | 1400 |
| Balsamic vinegar | 1.05 - 1.30 |
| Black liquid soap | 7,000 |
| Bleach (household 5 - 6 % sodium hypochlorite) | 1.53 |
| Brewers yeast | 368 |
| Butter fat @ 43°C | 42 |
| Caster oil | 250 - 500 |
| Citrus fruit pulp | 600 |
| Chocolate (49°C) | 17,000 |
| Chocolate syrup | 10,000 - 25,000 |
| Cocoa butter (60°C) | 50 |
| Condensed milk (75% solids) | 2,160 |
| Corn syrup | 2,000 - 3,000 |
| Fabric conditioner | 1,500 - 2,000 |
| Face cream | 100,000 |
| Glucose | 4,300 - 8,600 |
| Hair shampoo | 3,000 |
| Honey | 2,000 - 3,000 |
| Jam garnish | 8,500 |
| Laundry detergent | 1,500 |
| Liquid soap | 82 |
| Mayonnaise | 20,000 |
| Metallic auto paints | 220 |
| Milk | 2 |
| Milk condensed | 40 - 80 |
| Olive oil | 40 |
| Orange Juice Concentrate - 30 Brix | 630 |
| Orange Juice Concentrate - 60 Brix | 2,410 |
| Peanut butter | 150,000 - 250,000 |
| Printers Ink | 550 - 2,200 |
| Resin solution (from 18°C to 24°C) | 880 - 7,140 |
| Salad cream | 1,300 - 2,600 |
| Tomato ketchup | 50,000 - 70,000 |
| Toothpaste | 70,000 - 100,000 |
| Varnish paint | 140 |
| Water | 1 |
| Yoghurt | 152 |
Depending on the viscosity of the product, the pressure and flow rate needed to propel the produce out of its primary container and into its intended location will differ. For example, a thicker, more viscous product will require an increased force versus that of a runnier, more water-like product. The latter is generally easier to transfer because it can be helped by gravity and has less resistance. For many products, however, consumer perception is that the ‘thicker’ a product is, the more superior it is, as it is perceived to have been made with higher quality ingredients. This leads to many products being more viscous than they may actually need to be due to consumer perception driving sales, especially for example, beauty products like creams, hair conditioner or shower gel; and even household products like bleach, washing up liquid or laundry detergent.Working with high viscosities is usually far more challenging for flow-control engineers who need to move fluids through manufacturing lines, ensuring that the liquid is transferred at the correct speed, without damage and without waste. But it’s not just the baseline viscosity of the produce that needs to be taken into consideration, there are a few scenarios that can impact the viscosity and therefore change the properties of the product:
- Temperature – a colder temperature significantly increases the viscosity of a product making it more solid and less smooth/runny
- Head-height – should a product need to be propelled upwards, it’s working against gravity and will need a higher level of force to move it versus if it was to be released downwards or from above
- Molecular levels – gases and liquids hold different levels of viscosity and generally speaking, fluids with larger, more complex molecules or long-chain polymers (e.g proteins, starches, hydrocolloids or gums, etc) will also have higher viscosities
- Consistency – fluids with larger, more complex and inconsistent-sized ingredients will have higher viscosities e.g soup with ‘chunky’ components versus water
- Pressure – the lower the pressure applied to expel a food or beverage item, the slower it will run and the harder it is to drive and maintain the continuous momentum of the product
- Freshness/age – if not sealed aseptically, produce can deteriorate and break down either making the produce ‘runnier’, or it could solidify/crystallise to cause blockages.
- Rheology – some fluids shear thicken or shear thin as their flow velocity increases. Ketchup is a good example of shear thinning where it takes a lot of energy to start the fluid moving and then it becomes thinner. This is why you need to shake the bottle vigorously and then it suddenly pours out. Cornflower slurry is an example of shear thickening – the faster you stir it the stiffer it gets.
The optimal achievement of any pump is a near-vacuum (1 Bar negative pressure) so for a pump to self-prime the fluid must have a sufficiently low viscosity so that it can supply the inlet of the pump. The output of a pump is not constrained and may be several Bar. For extremely viscous liquids the fluid needs to be supplied to the pump using an independent pressure source.Overall, the key to moving viscous fluids is to choose the right pump. There are not many pump designs that can handle highly viscous fluids with precision. Quantex pumps use a positive displacement rotary action, so fixed volumes of fluid (boluses) are carried from inlet to outlet around a rotor – which produces inherently accurate doses and is much less sensitive to variables such as line pressure, fluid viscosity and flow rate. The positive displacement rotary action generates a high inlet vacuum and high pressure on the outlet. This means that, unlike other pumps, Quantex is able to transfer highly viscous liquids such as ketchup and mayonnaise, sour cream, jam, face cream, hair conditioner and even relish etc whilst being self-priming and with better bag evacuation and less waste. Quantex can even manage very thick fluids such as peanut butter with particulates, but it is necessary to encourage the fluid to the inlet side of the pump as the fluid is too thick to self-prime.The below videos show different solutions at various viscosity levels being expelled with the aid of a Quantex pump:
At Quantex, we understand the importance of viscosity, especially during manufacturing or within a retail or food service environment. And to serve these markets, we’ve developed a range of pumps to suit different flow rate ranges, viscosity levels and dispense applications and the technology holds over 100 global granted patents. Our High-Speed Eco Pumps use air pressure to activate the diaphragm and seal the pumps instead of a silicone spring, so they are more easily recycled, and can run almost three times as fast as our standard or high-pressure pumps.You can learn more about our pump range here:
If you’d like to learn more or discuss how a Quantex pump could work for you, please email Quantex.GeneralSupport@psgdover.com or call +49 (2065) 89205-0.