Freezing time depends on several factors, including the initial and final temperatures of the product and the quantity of heat removed, as well as dimensions (especially thickness) and shape of product, heat transfer process, and temperature.
“How long will this take to freeze or thaw?” This is a question that is regularly asked, and the short answer is always, “It depends!” I thought I would take an opportunity to build on Kristine’s fantastic article from August and highlight some of the history and science behind solid-liquid transitions as they occur in everyday foods and the complexity of why freezing and thawing can be so challenging.
The specific formulation of a product plays a role in freeze/thaw characteristics as well. When you have pure water, it will freeze at 32 degrees Fahrenheit. When water freezes under normal atmospheric conditions, adjacent molecules form hydrogen bonds and order themselves into a ring structure. This solid structure has lower energy than liquid water. When you have a solution of mostly water with some sugar dissolved in it, you will find the freezing point of the solution to be lower than pure water. Sugar dissolves readily in water and does not want to get out of the way to allow those hydrogen bonds to form. This makes it harder for water to freeze. The new lower freezing temperature will directly relate to the amount of sugar in the water. From the graph below, you can see the influence that dissolved solids concentration has on freezing temperatures. This also explains how in a common freezer a lower brix solution will freeze sooner than one at higher brix.
Just as there are a myriad of food combinations that we could freeze, there are many factors that come into play when we transition between a liquid state to a solid one. The first thing we must consider are the mechanics of heat transfer. There are three distinct types of heat transfer that have been classified based on the interactions required to transfer energy. Of these three, the two most heavily relied upon in the food industry are convection and conduction. Radiation will not be covered in depth here.
Freezing is a method of preservation that we have record of using as far back as 1100 BCE. Egyptians were chronicled to have used evaporative cooling to create ice used to maintain the quality of food during feasts (1). We have long understood the positive impact that reduction of heat energy has on the quality of our fresh and prepared foods. When we freeze or cool a product, we remove heat energy which in turn slows down chemical reactions and stabilizes the current state of fruits and vegetables. This works to reduce the negative effects of spoilage organisms, enzymatic degradation, natural separations, and to preserve beneficial vitamins and minerals.
So how can we know how long something will take to freeze or thaw? While none of the information presented directly answers this question, it should highlight the complexity of freeze/thaw systems and some of the interactions that play major roles in how long it will take to reach a desired state. The easiest way to determine a freeze time is to test it in a real-world scenario. Thermal data loggers can be put into product at various locations and set to record the temperature at given time intervals. Product can then be frozen with these active data loggers and then thawed to yield a good idea of how long it will take to freeze or thaw a product under a given set of circumstances. Keep in mind, if circumstances of your system change – air velocity or temperatures, temperature of incoming product, pallet stacking patterns, package material thickness, and formulation – expect an impact to the answer.
GCSE Chemistry – Factors Affecting the Rate of Reaction #47
FAQ
What can affect the freezing point?
What are the factors affecting freezing point solution?
What is the effect of freezing rate?
What is the cause and effect of freezing?
What factors affect the freezing rate?
Factors affecting the freezing rate include compositional and non-compositional influences. Generally, foods with the higher composition of fat and entrapped air will have lower conductivity. Non-compositional influences include air velocity, product thickness, agitation, degree of contact with the food and cooling medium, and packaging.
What are the effects of having a temperature above 43 degrees Celsius?
Hyperthermia is an elevated body temperature above the hypothalamic set point. It occurs when there is excessive heat production, reduced heat loss, or damage to the thermoregulatory centre in the hypothalamus. Temperatures >41°C or 98. 4°F are rarely the result of infections and usually imply loss of thermoregulation. A core temperature of more than 41°C is usually fatal and is associated with sweating, extreme tachycardia and hyperventilation. Seizures, loss of consciousness, confusion, and pulmonary edema with shock and multiorgan failure occur in advanced cases.
What are the disadvantages of freezing?
Other disadvantages of freezing include the following: • freezing injury of unpackaged foods in slow freezing processes causes cell-wall rupture due to the formation of large ice crystals;
What happens if the freezing rate is too fast?
In general, it holds that the faster the freezing rate the smaller the ice crystal size. Yet for some food materials there is an upper limit for the freezing rate. If freezing is too fast, mechanical stresses are imparted to the food material and freeze fracturing can occur.