That none should perish, but have eternal life — Perishable foods

There’s no use crying over spilled milk — it’ll spoil eventually anyways.

This is second post in a series on the 5 kinds of food. You can read the first part and introduction here.

For reference, here are the five categories of food. We’re going to start with Perishables and work our way to the right.

The first and most abundant type of food is perishable food. Perishable food is different from non-perishable food because, well, it perishes. Perishable foods have a limited shelf-life and generally need to stay cold to be preserved. Even when refrigerated, perishable foods often have a shelf life on the order of days, weeks, or months. Microbes are present in perishable foods and over time, grow and spoil it. Microbial growth is however strongly dependent on temperature and most begin to die at temperatures about 55°C.

A peach is a terrible thing to waste. This one has been left out for a few days to see what happens. The peach itself is losing moisture to the environment, meanwhile, mold spores on the peach’s surface are slowly growing and eating what’s left of the fruit. Mold spoilage is the most common kind of microbial spoilage and it doesn’t make food unsafe, just really nasty. (Image: http://oer.nios.ac.in/wiki/index.php/Food_Spoilage)

There are a lot of different strategies to kill microbes in food but the most common and time-tested method is: Heat. Heating foods to certain temperatures for certain lengths of time kills microbes that could cause spoilage or illness, preserving foods for longer or making foods safe to eat. Heat, however, does not always kill everything. Some bacteria and fungi are able to survive fairly high temperatures (they’re appropriately called “thermophiles”) and some, form hard, impenetrable coatings called ‘spores’. Spores take some considerable extra effort to kill and we’ll discuss them when we get to another category of foods — low acid canned foods.

This amazing electron microscope image shows a Clostridium spore germinating into a cell. The image is colored for clarity (I’m not sure what color exactly is at a 100 nm scale). The part that looks like a burlap sack is the spore coat, a tough coating which can protect the cell inside from drying for millennia. We’ll talk about spores and Clostridium in due time. (Image: https://www.sciencedaily.com/releases/2015/05/150513102754.htm)

By weight, water is the main ingredient in just about all perishable foods. (You can read more about water and its importance here). This means there’s abundant water in these foods to support microbial growth but it also means that these foods are difficult to heat to temperatures above 100 C. This is important because bacterial ‘spores’ are only killed by heat at temperatures greater than 100 C so using heat to kill all microbes (spores and the regular kind, called ‘vegetative cells’) is only possible if the food is cooked under pressure. Pressure allows us to increase the boiling point of water above 100 C so we can cook foods at higher temperatures without drying them out. We’ll see just how important this is when we discuss low acid canned foods.

Microbes are not too different from us. They need three things to grow and flourish: water, food, and a hospitable environment. Perishable foods don’t totally deprive microbes of any of these. They have available (unbound) water, nutrients, and aren’t inhospitable. As we’ll see from the other kinds of foods, this makes them unique.

Microbes need the same things we do for survival: food, water, and shelter (some also need air). Non-perishable foods deny microbes one of these key elements, denying them a place to grow and spoil food.

Because microbes can easily grow in perishable foods they often need to be cooked before eating. Perishable foods are easy to contaminate with fresh microbes so they have to be properly handled (all food does, but this category especially). This can pose higher risks, particularly for perishables that are eaten raw.

Now the exact definition of ‘perishable’ can change in the context of perishable foods. Raw potatoes and raw milk are both perishable foods but have substantially different time-scales. Potatoes, if properly stored could last months or even a year; raw milk might last hours to days. To be clear, cooked foods are still perishable too. Non-perishables must deny microbes at least one item required for growth and maintain that condition until the food is consumed. In general, perishable foods lack a control mechanism that the other categories have.

The fact that perishable foods spoil is their key drawback. In many parts of the world where refrigeration and distribution are not well established, perishable foods can be an enormous contributor to food waste. Even in developed countries, perishable foods still contribute enormously to food waste. As much as half of the produce grown in the US can go straight in the trash for reasons as silly as cosmetics. Preserving foods gives us a way to store foods in times of abundance for leaner times and processing foods can often find a home for ingredients that are perfectly delicious, but maybe a bit ugly. Food preservation a critical part of our shared humanity and a reason why humans have been so successful at surviving hard times.

I have no f’ing clue how non-alcoholic beer is preserved.

By the way, if you’re still waiting for the answer to my question from this post. The answer is non-alcoholic beer. I’ll be honest, I have no idea how non-alcoholic beers are preserved. They don’t seem to fit any category. I’ll do some research and get back to you…

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