Food tech advancements help feed astronauts on space stations and folks on Earth who are hungry at 3 am. We’ve figured out ways to keep milk fresh for months, cook rice faster, and dehydrated mummy’s pav bhaji so it’ll last through lonely semesters abroad. Here are some of the processes behind the most common preserved foods.
Dehydration: Every culture in history has figured out that leaching moisture from a food item can make it last longer. This began as a way to preserve certain foods through ingredient-scarce winters or during long journeys. Sundried tomatoes, air-dried fruit and cured fish and meats all started out this way. Electric and microwave dryers use the same principle to create soup mixes, noodle garnishes, long-life spice and trail mixes. Some dehydrated foods, raisins for instance, can last years if properly dehydrated.
Spray-drying: Used most commonly for milk and coconut milk powder, it exposes the liquid to a blast of hot gas to quickly let the moisture (but not the fat) evaporate, leaving a fine-particle powder behind. Dried eggs, instant coffee, fruit juice and honey powders and flavourings are made in much the same way, and shelf lives range from weeks to years.
Freeze-drying: High-tech, but really simple. Food is frozen to a low temperature to turn its moisture into ice. The water is then sublimated, turning the ice directly into vapour that is sucked away. What’s left is room-temperature food that retains most of its nutrients, with taste, colour and shape intact too. Most freeze-dried foods can last years. This method is most commonly used for fresh fruit and vegetables, and pet food.
Flash-freezing: As the name suggests, fresh food, fish or meat is put into an air- or brine-based freezer. Commercial versions do the freezing in as little as two minutes. Speed is essential; it prevents the food from forming ice crystals that might break down its cellular structure, compromising on flavour and texture, and drying it out. Most flash-freezing is done immediately after harvest, yielding foods that are fresher than the ones sitting on supermarket shelves.
Reconstituted food: These are the dried foods that you “just add water to” to revive. Think of preserved mushrooms, instant oats, noodles. Potato reconstitutes well too — it’s what makes mashed-potato mixes and instant-aloo-sabzi kits so popular in fast-food kitchens. Most packages last 18 months.
Irradiation: This no-heat process can kill bacteria, mold and pests that would have made fresh meats and farm produce rot faster. The World Health Organization and Food and Agriculture Organization have declared it to be safe. But there aren’t enough studies on the long-term effect of this ionising method on humans, so several countries, particularly those in the European Union, prohibit its use.
Retort: The tech was developed in the US to feed astronauts during long spells in space. There’s no heat, no chemicals, no exposure to gas, just filtered water and extreme pressure. Cooked food is sealed in flexible, multilayer pouches and sterilised under pressure (in a process called Pascalization) to destroy microorganisms but retain nutrients. Food in these pouches can last more than a year at room temperature. It started out being better suited for Western food – oils and spices don’t take well to the process. But recipes for biryani and curries have since been developed, allowing for more diversity.
Modified atmosphere: Another way to preserve food is to replace or deplete the oxygen around it. Oxygen helps microbes grow; in preservation, the less of it there is, the better. This is why salad greens are often packed with dry ice at the bottom, slowly increasing carbon dioxide levels in the container. It’s why food is vacuum-packed. And why potato-chip packets are inflated with nitrogen.
Ultra-Pasteurisation: Sure, boiling milk makes it last longer. But new dairy processes take it a step further. They boil milk to 137° Celsius for just a few seconds and then rapidly cool it, which kills more bacteria. This, along with sterile packaging, creates long-life milk, which can last six months outside a refrigerator, unopened.