Specific heat tells you how much a product "resists" being cooled. At 4.19 kJ/kg·K the specific heat of water is one of the highest values known; that of air is around 1.0, of steel 0.5 and of ice 2.1. Because most foods consist largely of water, their values follow the water content: lettuce and cucumbers 4.0, apples and oranges 3.6–3.8, lean meat and fish 3.3–3.6, fatty meat 2.5–3.0, butter and dry products 1.5–2.5 kJ/kg·K. The higher the water content, the more energy it takes to cool the product.
Below the freezing point the value falls to about half, because the water is now ice: frozen meat and fish 1.7–1.9, frozen fruit and vegetables 1.8–2.0 kJ/kg·K. That is why two separate specific heats are given for every product: above freezing and below freezing. A freezing calculation has three parts: sensible heat down to the freezing point (specific heat above freezing), latent heat during freezing and sensible heat from the freezing point to the final temperature (specific heat below freezing). The largest share belongs to the latent heat.
The calculation is a single line: heat = mass × specific heat × temperature difference. Example: 1,000 kg of apples are to be cooled from 25 °C to 0 °C; 1,000 × 3.65 × 25 = 91,250 kJ, that is, about 25 kWh of heat must be removed. If this is to be done in 20 hours the product load is 1.3 kW; if in 5 hours, 5 kW. Same product, same heat; the shorter the time, the greater the cooling capacity needed. This is the reason why pre-cooling and blast freezing rooms are many times more powerful than storage rooms.
The forgotten item is the packaging. Wooden pallets and crates (about 2.0–2.5), cardboard (1.4–1.7), plastic crates (1.7–1.9) and steel trolleys (0.5 kJ/kg·K) are also cooled along with the product; with heavy wooden crates the packaging can reach 10–15% of the product load. The specific heat values in reference sources are averages; they vary by a few per cent with variety, ripeness and fat content, and in the calculation this difference is covered by the safety margin. When you select the product in the cooling load calculator the specific heat value is filled in automatically; the product data is shared with the food storage conditions guide.