Freezing for Slicing Bacon
By Eben van Tonder
Just after we commissioned our high-speed slicer, I did some reading up on the matter of freezing bacon for slicing. Here I share some notes and comments about freezing bacon for slicing.
People want to buy their bacon ready sliced. When producing pre-sliced bacon with a high-speed slicer, slicing temperature is of the greatest importance. If the temperature of the bacon is too low, the blade of the slicer will be subject to excessive wear and the bacon will shatter. If the temperature is too high, the soft bacon sticks to the blade and the fat are torn away from the lean.
There have been many experiments to try and determine the optimum slicing temperature. Salt percentage has a huge influence on the freezing point of the bacon. However, the exact salt percentage varies greatly in bacon, even bacon in the same batch. The other variable is the particular slicer used. Other factors that affect slicing temperature are maturing time, the water content and the blade speed. These variables are so great that a general rule in terms of slicing temperature is impossible. Slicing temperature must be determined experimentally on the ground and adjusted per batch. (Evans, J, 2080: 137, 138)
The slicing manager must develop practical experience and be constantly aware of the temperature of the bacon and the resultant slice quality. He or she will get to know the different slicers and the different bacon cuts (back, belly, leg, neck, shoulder) and will have to adjust the temperature and blade speed in order to achieve the best slicing results.
There is not an exact definition of what tempering is in the meat industry. The term generally refers to either lowering or raising the temperature of meat to prepare it for the next processing stage. It includes thawing meat for processing or setting the meat at an optimal slicing temperature. (James, S. J, et al; 2002: 149)
Single Stage Tempering for slicing
It is important to have the right stiffness in the meat when sliced with a high-speed slicer (800 – 1400 slices per minute). This is achieved by presenting the bacon log to the slicer in a semi-frozen or frozen state. If the temperature is not optimal, meat texture is damaged in slicing which leads to a loss in slicing yield. (James, S. J, et al; 2002: 149) Single-stage tempering is when the bacon joints are put on a trolley, wheeled into a freezer that is set at slicing temperature and it remains there until the bacon has reached slicing temperature, evenly throughout the meat.
In experiments, pork loins were held in a room set at – 18 deg C. After 18 hours the surface was at – 10 deg C, but the center was still well above – 7 deg C. An average weight loss of 1.88% was observed over this time, increasing by another 1.88% if the meat was held for a total of 64 hours (which can happen over week-ends). (Evans, J, 2080: 139)
The biggest problem with the single-stage tempering system is that the single tempering system has to fulfill conflicting roles. It must remove temperature from the bacon and in order to achieve this, a reasonably large temperature difference is required between the bacon and the air as well as air movement. Then, towards the end of the process when the heat has been removed, a small temperature differential and minimal air movement are required to attain an even temperature and to reduce the rate of weight loss. (Evans, J, 2080: 139)
The other large drawback is, of course, that of space. Large refrigeration rooms will be required to perform this step over a long time period.
Two-Stage Tempering for slicing
In this system, the bacon is blast frozen and then placed in an equalizing freezer. The objective of blast freezing is to remove the required amount of heat. (Evans, J, 2080: 139)
Here, a large difference in temperature between the bacon and the air is achieved as well as air movement. (Evans, J, 2080: 139)
An economical objective is to try and have both stages completed under 8 hours. Two factors that will extend this time are if, during the initial blast freezing, either too much or to little heat has been extracted. (Brown, T, et al, 2003: 690 – 697)
The longer the bacon has been in blast freezing, the lower the equalization temperature would be. (Brown, T, et al, 2003: 690 – 697)
Generally, the longer the total processing time, the more the weight loss will be. In the end, the correct slicing temperature is probably more important than the small weight loss brought about by a longer processing time. What is of the utmost importance to the quality of the bacon cuts are at the correct slicing temperature. (Brown, T, et al, 2003: 690 – 697) If the total two-stage processing time is extended beyond the 8-hour target in order to obtain the correct slicing temperature, this is better than not achieving the required temperature in the meat.
“Optimising a two-stage tempering system using a purely empirical technique would be a costly, labour intensive process. Reliable predictive techniques would substantially improve the process.” (Brown, T, et al, 2003: 690 – 697) Such a process must be developed in each factory.
Freezing times and purge
Rate of freezing is one of many factors that impact on the occurrence of purge or syneresis after packaging due to damage of freezing to the muscle structure. (8) Purge is when, after the bacon has been packed and is thawed out to a temperature of between 0 and 5 deg C, there appears a liquid in the packaging. The same is true for thawing which also damages the muscle structure and produces drip loss. (James, S. J, et al; 2002: 278)
Freezing, in general, always reduce the water holding capacity of the meat and therefore increases drip loss. (James, S. J, et al; 2002: 37)
Slow freezing produce large extracellular columns of ice of greater continuity than the small intracellular ice crystals formed during fast freezing (James, S. J, et al; 2002: 278)
At slow freezing the extracellular water freezes first. As freezing continues, the ice crystals grow. This can result in salt crystallization and even pH changes.
Repeated freeze-thaw increases drip loss. (James, S. J, et al; 2002: 39)
Brown, T, et al. 2003. Practical investigations of two-stage bacon tempering. International Journal of Refrigeration 26 690–697.
Daily Telegraph, Launceston, Saturday 2 February 1901. Article: Bacon curing.
Daily Telegraph, Launceston, Tuesday 26 April 1910. Article: Bacon curing.
Evans, J. 2080. Frozen Food Science and Technology. Blackwell publishing.
* James, S. J, and James, C. B. 2002. Meat Refrigeration. Woodhead Publishing Limited.
Kennedy C. J. 2000. Managing Frozen Foods. Woodhead Publishing Limited.
Smith, Edward. 1873. Foods. Henry S King and Co.