Forty litres of soup and a thermometer that lies
You are making 40 L of vegetable-beef soup for a charity lunch serving 150 bowls between 12:00 and 2:00 p.m. The soup finishes at 9:00 a.m. Two lidded 20 L stainless stockpots sit on the prep table until 10:15, then go into the walk-in (3°C). At 11:45 the first pot is reheated; the fastest you can manage takes 35 minutes and the centre reaches 68°C. It goes into a chafing dish at 11:55 and holds at 57°C. At 12:20 the second pot comes out of the walk-in at 8°C. The only probe thermometer reads 2°C in an ice-water bath. There is no written temperature log anywhere.
1. Evaluate the cooling of the two pots. What do you do with the second pot that reads 8°C at 12:20?
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The clock starts when the soup drops below 60°C. The standard is 60°C to 20°C within 2 hours, then 20°C to 4°C within 4 hours - 6 hours total. A 20 L pot is about 30 cm deep, so the centre cools far more slowly than the edges, and 75 minutes on a table is only harmless while the pot is still above 60°C.
For the second pot at 8°C at 12:20: 8°C is not safe, it is mid-danger-zone. To judge it you need to know when it crossed 20°C. With no log, you cannot show that - and the default when you cannot demonstrate safety is to discard.
The practical decision for the lunch: reheat that pot to 74°C now, use it as the next batch, and do not try to hold a half-cooled pot for later. For future batches, cool in shallow pans no more than 5 cm deep, use an ice bath or an ice paddle, stir, and write the time and temperature down at each stage. A 20 L pot in a full walk-in almost always fails the 2-hour first stage.
2. Evaluate the reheating and hot-holding of the first pot, and give the corrections.
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Reheating. Leftovers and previously cooked food must be reheated to 74°C within 2 hours, once. Reaching only 68°C means the food has spent 35 minutes climbing through the danger zone and still has not hit the target. Correct it by reheating in smaller batches on high heat, stirring, and probing several spots including the centre of the thickest mass.
Hot holding. 57°C is below the 60°C minimum, so the soup is now sitting in the danger zone while it is being served, and the chafing dish is losing the race. Immediate fixes: return the pot to the range and bring it back to 74°C, add fuel or hot water to the chafing dish, hold at 60°C or above, and check and record every 30 minutes. If the setup cannot hold 60°C, serve in smaller batches replenished from the stove rather than holding a large volume at the wrong temperature.
Two rules to state out loud: reheat only once, and any soup that has been through service is discarded - never cooled, stored, and reheated a second time.
3. The probe thermometer reads 2°C in ice water. What does that mean for your decisions, and what do you do?
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An ice-water bath is 0°C, so a reading of 2°C means the thermometer reads about 2°C high. That makes every measurement optimistic: the soup you measured at 68°C was really closer to 66°C, which is further from the 74°C target than it looked. It also means the 57°C holding reading may have been nearer 55°C, and the second pot may have been warmer than 8°C.
What to do:
- Calibrate now using the ice-point method - adjust the nut or record the offset - and re-check against boiling water if you can. Replace it if it cannot be adjusted.
- Sanitize the probe before and after each use, especially between raw and cooked foods.
- Measure the centre of the thickest part, not the edge or the surface.
- Start a written log of cooling, reheating, and holding temperatures with times and initials. Without records, an inspector - or you, three hours later - cannot tell whether the food was safe.
A thermometer you have not checked is worse than none, because it gives false confidence.