More+Solid+Than+Liduiq


 * __ More Solid Than Liquid __**

Ever thought of fruit juice as a solid? It may surprise you to know that we can show it's more solid than liquid for a great period of time. Elasticity can be measured with an oscillatory rheology test and //phase angle // is the parameter we use to quantify it. Simply put, an oscillation measurement on a solid will report a phase angle of 0°: purely elastic behaviour. Conversely, a liquid – completely //in //elastic (or //viscous, // as we rheologists call it) – results in a phase angle of 90°. This gives us a scale of “solidity” and therefore a measure of the presence of elastic network structure.

Below is the result of an oscillation stress sweep test on mandarin juice - with phase angle plotted as a function of applied stress:

 

 At low stresses we can clearly see a plateau at a phase angle of around 18°, telling us that the juice, under these gentle, virtually at-rest conditions, possesses a very well developed soft-solid structure. In other words, the juice would be more accurately describe as a solid than a liquid! The reason we don’t see this is that the structure is so weak it is completely disrupted at the slightest disturbance, leading to viscous, liquid-like behaviour. The graphic below shows a comparison of the juice alongside a smoothie and a yoghurt:

<span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%;"><span style="background-color: #ffffff; color: #000000; font-family: 'Times New Roman',Times,serif;"><span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%;">

<span style="background-color: #ffffff; color: #000000; font-family: 'Times New Roman',Times,serif;"><span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%;"> <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt;">As you can see, all three show similar “solidity” at lower stresses, the only differences being in the strength of the structure, which in smoothie and yoghurt are strong enough to make the soft-solid condition noticeable to the casual observer.

<span style="background-color: #ffffff; color: #000000; font-family: 'Times New Roman',Times,serif;"><span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%;"> <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt;">So how can we use this information? <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt;">Well, structure, even extremely delicate ones such as we see in the fruit juice, contributes to many desirable characteristics inother food and beverages as well as pharmaceuticals, cosmetics, paints and many other materials, for example:

<span style="font-family: 'Arial','sans-serif'; font-size: 10pt;">Penetration, sagging and slumping <span style="background-color: #ffffff; color: #000000; font-family: 'Times New Roman',Times,serif;"><span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%;"> <span style="background-color: #00ffff; color: #000080; font-family: 'Comic Sans MS',cursive; font-size: 10pt; lineheight: 115%;">Dear fellow food techies, so now we know that when fruit juice is in the carton on the shelf it is a solid – well, more solid than liquid anyway!
 * <span style="color: black; line-height: normal; margin: 0cm 0cm 10pt; mso-list: l0 level1 lfo1; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt;"><span style="font-family: 'Arial','sans-serif'; font-size: 10pt;">Suspension stability
 * <span style="color: black; line-height: normal; margin: 0cm 0cm 10pt; mso-list: l0 level1 lfo1; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt;"><span style="font-family: 'Arial','sans-serif'; font-size: 10pt;">Texture and appearance
 * <span style="color: black; line-height: normal; margin: 0cm 0cm 10pt; mso-list: l0 level1 lfo1; mso-margin-bottom-alt: auto; mso-margin-top-alt: auto; tab-stops: list 36.0pt;"><span style="font-family: 'Arial','sans-serif'; font-size: 10pt;">Pouring, draining and dripping