Food safety is something the home cook thinks they understand, but probably you probably want a bit more information on the subject. It would be my feeling that a home economics class in this would make more sense than cooking french toast.
Food needs to be handled with care as well as respect. While we have have seen the food industry get better about food safety, it is still a few times a year we hear of an outbreak of some sort of food borne illness. I will go into detail on that later, but you need to learn the biggest potential problem that exists, and its what we call time and temperature abuse.
NOTE: all apologies to my Celsius contingent. All temps are in Fahrenheit, I will put a Celsius break down at the bottom,
THE LOWS ( less than 41° )
Food has two states when it is under 41°, it is refrigerated or frozen with a freezer typically at 0° or less. Refrigeration works best when there is room for air to move around products and cool it evenly. It also is best not to throw something hot, right in your refrigerator because it will have to work overtime to cool the entire space. We will go into rapid cooling in a bit.
Freezers need to be kept very cold, this is so that product freezes fastest and the food can survive the defrost cycles. I know we all like our ice cream soft, but its worth it, trust me.
THE HIGHS ( more than 140° )
In the Thermometer article we discussed the final cooking temperatures, and they do stand as a guide along with this. You will not that the temps all tend to be above 140° which is the top end of the zone.
( 41° – 140° )
Now what is left? The space between is called the Danger Zone. Why is it named for a Kenny Loggins song? well, its not, it is named because this is the zone when bacteria growth is optimized and given the perfect conditions to grow. Bacterial can double in number in as little as 20 minutes. So, in the course of 3 hours 100 bacterium would become 25,600 and it gets exponential from there. Leave it out overnight? how about 838,860,800?
HYPER ZONE ( 72°-90° )
Now there is one section where it is prime time for Bacteria, and that is called the Hyper-Danger Zone. This is when growth is maxed out and bacteria will flourish. Keep food out of this zone.
You can see in the above example that temperature is half of the problem. Surely when you cook something from frozen it has to travel through the danger zone, right? Well just as if you were in a city, and had to get through a bad part of town, you would pick the shortest route through there right? You are not exactly going to hang out and go sight seeing while the dangerous elements gather, right?
The other thing to take into account is that time goes both ways. This applies to cooking as well as cooling. You must cool food quickly in order to keep it safe. Leaving that pot of soup on the stove to cool down after cooking is not a good idea.
So, knowing that it takes both time and temperature to cause bacteria to grow, what can you do about it? Well the answer is follow some simple guidelines.
- Invest in a decent pocket thermometer to test items quickly
- Always minimize time product has to be in the danger zone by cooking rapidly when possible
- Some food is more prone to bacterial growth than others. a mayonnaise based salad might be more prone to growth than say a steak. Just because it is not a cooked product does not mean this does not apply!
- Never leave food in the danger zone more than 4 hours; and the Hyper Danger Zone no more than hours. An important note, that timer is reset when food is reheated back up to its final cooking temperature and held for 15 minutes.
- Time is accumulative. That is to say if you leave it out for 1 hour, take it to a picnic that is 2 hours away, and leave it out for an hour, you have maxed out your time! Plan ahead, and be safe.
This really is important when it comes to thawing food. The best practice is to plan ahead and thaw under refrigeration entirely. To speed things up you can keep a thermometer on things and when you see the temp getting near 35°, put it back in the fridge and let it finish out in there.
If you must thaw under pressure, the method I recommend is the one from the scallop article.
“under cool water (72 degrees or less) and wrapped in plastic zip top bags so water does not touch the flesh. I double bag mine just to be sure. The scallops should remain under water at all times with the water running into the container at all times. This can thaw them in quick order, about 15-30 minutes.”
Cooling is just as important as cooking, and in most cases, even more so. One needs to make sure they can cool the product as fast as possible. When I am making a soup for instance I will actually throw some stock “ice Cubes” I have in my freeze into the soup when I pack it up to help cool it faster.
Another method is to place what you are cooking in a pan that will have the most surface area and spread it out the most, so when you put it in the fridge, it will cool the fastest. You can then put it in its long term container. Stir any of the products frequently. Ideally, you want to cool a product down to 72° in 2 hours and then below 41° in a total of 4 hours.
RUN A TIMER USE A THERMOMETER
When it comes to safety, err on the side of common sense. I would even have a timer set to make sure I am cooling something that might not cool as fast as I would like. An example would be when I make a gallon of tomato sauce at home. I usually will pour it into a flat pan, like a cake pan and cool it with plenty of circulation.
I have even been known to put things outside, well covered of course, when the temps are below 30° (in the shade, mind you). Why tax my refrigerator when the outside is willing to do the hard work!
FOR THE CELCIUS INCLINED (taken from here)
“Most of the pathogenic bacteria in food multiply rapidly between 10° to 60° Celsius (the “danger zone”). That is the reason why cold food always should be stored lower than 7 degrees in the fridge. This slows down the growth of bacteria. Cooked food should at least be heated to 70 degrees Celsius in the centre for 2 minutes. Cooking at temperatures between 70° and 100°C kills most bacteria but some spores can survive and can give rise to growth of bacteria if food is later stored below 60°C”
A great resource : http://www.foodsafety.gov/