Thawing, cooking, cooling and reheating

Between the walk-in and the plate, food goes through the steps where most temperature mistakes happen. Frozen food has to thaw without warming up on the outside while the centre is still frozen. Raw food has to be cooked hot enough, for long enough, to kill the pathogens in it. Cooked food that will not be served right away has to cool quickly enough that spores cannot wake up and grow. And food that was cooked and cooled earlier has to be reheated fast and hot. Each step has limits, and the kitchen has to meet them on a Saturday night as well as on a quiet Tuesday.

Thawing

Frozen food thaws from the outside in. If a frozen turkey breast is left on the counter, its surface reaches room temperature and spends hours in the danger zone while the middle is still frozen solid. Bacteria on the surface, which survived freezing, start to grow long before the food is ready to cook. That is why thawing at room temperature is never allowed. There are four safe methods.

• In the cooler, at 4 °C or colder. This is the safest method but the slowest; a large roast or a case of chicken can take a day or two, so it needs planning. Thaw on a tray on the bottom shelf, below ready-to-eat food.
• Under cold running water, with the food in its wrapping or a sealed bag, fully submerged, and the water running fast enough to carry away loose particles. The water must be cold, and the sink must be cleaned and sanitized before and after.
• In a microwave, but only if the food will be cooked immediately afterwards, because microwaves thaw unevenly and leave warm spots.
• As part of cooking, such as frozen fries going straight into the fryer or frozen burger patties going straight onto the griddle, as long as the food reaches its full cooking temperature.

Vacuum-packed frozen fish needs extra care. Clostridium botulinum type E, which is found in fish, can grow and make toxin at cooler temperatures than most pathogens and grows without air. Fish labelled to be kept frozen until use should be taken out of its vacuum package before it thaws, or thawed in the cooler and opened immediately, never left sealed and thawing in a warm place.

Cooking

Cooking is the step that kills the pathogens that came in with raw food, and it is one of the few steps where a single number decides whether food is safe. The right number depends on the food: poultry, which often carries Salmonella and Campylobacter throughout, needs a higher temperature than a whole steak, whose inside is normally sterile and whose bacteria are on the surface. Ground meat is in between, because grinding spreads surface bacteria through the whole batch.

Juniper's line cooks probe every chicken dish, every burger and every egg dish that is held, and record a sample of readings on the cooking log at each service. Steaks and fish cooked to order are usually judged by experienced cooks by touch, but a probe settles any doubt. Colour is not a reliable sign of doneness: ground beef can turn brown before it is safe, and poultry juices can run clear while the meat is still too cool.

Why time matters as well as temperature

Heat kills bacteria gradually, not all at once. At any given temperature, a fixed share of the bacteria die every second, and the hotter the food, the faster they die. That is why cooking standards sometimes pair a temperature with a time, and why a whole roast can be made safe at a lower temperature if it is held there long enough. Food scientists describe the goal as a log reduction: a 7-log reduction of Salmonella in poultry, for example, means that only one cell in ten million survives. The single numbers in the table are set high enough that the reduction happens almost instantly, which is why a cook only needs to see the probe reach the number.

Sous vide cooking, in which vacuum-sealed food is cooked for a long time in a precisely controlled water bath, uses the same principle to cook chicken safely at temperatures well below the usual standard. It is a legitimate technique, but it combines low cooking temperatures with packaging that removes air, which favours Clostridium botulinum, so restaurants need a written process with time and temperature tables, fast chilling and strict storage limits, approved by the health authority. Juniper does not cook sous vide; if it ever starts, the process will go into the food safety plan first, as Lesson 11 describes.

Partial cooking

Some kitchens partly cook foods in advance to save time during service: blanching fries, par-roasting chicken wings or searing burger patties to finish later. Partial cooking is risky because it warms the food into the danger zone without killing everything in it. It is allowed only under a written procedure: the initial heating lasts no longer than an hour, the food is cooled immediately using the two-stage limits, it is stored cold and labelled as partly cooked, and it is cooked to its full temperature before it is served. Juniper's wings are fully cooked, cooled and then reheated and crisped to order, which is simpler to control.

Undercooked foods on the menu

Many guests want a rare steak, a soft-poached egg or a tuna tartare, and restaurants can serve them with care. Whole cuts of beef can be served rare because the inside of an intact steak is normally free of bacteria and the outside is seared. Ground meat is different: BC health authorities expect hamburgers to be cooked to 71 °C, and a restaurant that wants to serve undercooked burgers needs a special process, such as grinding whole cuts in-house after searing their surface, written into a food safety plan and approved by the health authority. Raw fish must be frozen for parasites, as Lesson 3 described. Juniper's menu tells guests which dishes are served raw or undercooked so that people at higher risk can choose something else.

Cooling

Cooling is where many of the worst restaurant outbreaks begin. A big pot of chili, stock or braised beans is cooked properly and then left to cool on the range or in a deep container in the walk-in. The outside cools; the centre stays warm for many hours. Clostridium perfringens and Bacillus cereus spores, which survived the cooking, germinate and multiply, and by morning the batch can make dozens of people sick. Because large masses of food cool very slowly on their own, the rules set strict limits on how fast cooling must happen.

BC uses two-stage cooling, as written into food safety plans such as Island Health's: cooked food must cool from 60 °C to 20 °C within 2 hours, and then from 20 °C to 4 °C within a further 4 hours, for a total of no more than 6 hours. The first stage is shorter because bacteria grow fastest between about 20 °C and 50 °C. If the food has not reached 20 °C within 2 hours, it is reheated to 74 °C and the cooling starts again, or it is thrown out; if it has not reached 4 °C within 6 hours, it is thrown out.

Cooling methods that work

• Divide it. Pour soups, sauces and stews into shallow pans no more than about 5 cm deep, and cut large roasts into pieces no bigger than about 2.5 kg.
• Use an ice bath. Set the pot or pans in a sink of ice and water, and stir often so the warm centre moves to the cold edge.
• Use ice paddles. Plastic paddles filled with water and frozen can be stirred through a pot of stock to pull heat out from the inside.
• Add ice as an ingredient. For a soup or sauce made with water, cook it with less water and add the rest as clean ice at the end.
• Use a blast chiller. Juniper bought one in its second year, after the rehearsal dinner, and it cools a full pan of braised short rib to below 4 °C in about 90 minutes.
• Leave it uncovered at first. Food that is still cooling goes on the top shelf of the walk-in, loosely covered or uncovered, with space around it, and is covered once it is cold.

Cooling is a critical control point in Juniper's food safety plan, so every batch of soup, stock, sauce, braised meat, beans and cooked grains is logged: the time it came off the heat and its temperature, then readings at about one, two and later hours until it is cold. The program below checks three entries from the cooling log against the two-stage limits.

# Check invented cooling logs against two-stage limits (BC): 60 -> 20 C in 2 h, -> 4 C by 6 h.
logs = {
    "chicken stock (shallow pans, ice bath)": [(0, 62), (1, 38), (2, 18), (4, 7), (5.5, 4)],
    "short rib (blast chiller)":              [(0, 66), (1, 24), (1.5, 3)],
    "black beans (deep pot, walk-in)":        [(0, 61), (1, 49), (2, 36), (4, 22), (6, 13)],
}

def temp_at(log, hour):
    """Latest reading taken at or before the given hour."""
    readings = [t for h, t in log if h <= hour]
    return readings[-1] if readings else None

for name, log in logs.items():
    stage1 = temp_at(log, 2)
    final = temp_at(log, 6)
    problems = []
    if stage1 is None or stage1 > 20:
        problems.append(f"stage 1 failed ({stage1} C at 2 h): reheat to 74 C and restart, or discard")
    if final is None or final > 4:
        problems.append(f"not at 4 C by 6 h ({final} C): discard")
    print(name)
    print("   " + ("PASS" if not problems else " / ".join(problems)))

chicken stock (shallow pans, ice bath)
   PASS
short rib (blast chiller)
   PASS
black beans (deep pot, walk-in)
   stage 1 failed (36 C at 2 h): reheat to 74 C and restart, or discard / not at 4 C by 6 h (13 C): discard

The stock in shallow pans and the short rib in the blast chiller both pass. The black beans, cooled in a deep pot in the walk-in, fail the first stage, and because nobody acted at the two-hour check, they also fail the second. At the two-hour mark, the cook could have reheated them and restarted the cooling in shallow pans; by the six-hour mark, the only safe choice is to throw them out. That is the value of the log: it turns a hidden problem into a clear decision while there is still time to make it.

Reheating

Food that was cooked and cooled properly and is being reheated to be held hot must be reheated quickly: to an internal temperature of 74 °C within 2 hours, as Island Health's food safety plan template sets out. Reheating slowly in a steam table or a warming cabinet is not allowed, because the food would spend too long in the danger zone. Juniper reheats on the range, in the combi oven or in the microwave, probes the food, and only then moves it to the hot holding unit. Leftovers are reheated only once; anything left after that service is thrown out.

For supervisors: planning for safe batches

• Make batches no larger than you can cool. A 40-litre stockpot of chili is easy to cook and very hard to cool; two 20-litre batches made at different times, or one batch split into shallow pans, are much safer.
• Schedule cooling for when people are around. A batch that comes off the heat at 9:30 p.m. needs someone to check it at 11:30 p.m. and later. If nobody will be there, cook it earlier or use the blast chiller.
• Thaw by plan, not by panic. A thawing schedule on the walk-in door, filled in when the next day's prep list is written, keeps cooks from reaching for the counter or a hot water tap.
• Probe and log, then train with the log. The cooling and cooking logs show which batches cause trouble and which cooks need help.