Intro to Food Preservation
I get a lot of requests to talk about food preservation. There are two major questions to answer with respect to that:
- Is this food safe to eat?
- Is this food still pleasant to eat?
Both of these have the related corollary question “how can I maximize the quality and safety of food I’m storing for the longest amount of time?” Some guidelines (e.g.: “best by” date labeling) are because the quality will tend to deteriorate even though the preserved food may be completely safe to eat.
A little about me: I cook a lot, mostly dinner at home for my family and friends but sometimes for massive parties of upwards of 200 people. I’ve been doing sous vide cooking since 2010. I run a food blog called Unselling Convenience (also @unsellingconvenience on Instagram if you’d rather follow along there), which is mostly an inspiration board and memory database of things I’ve enjoyed cooking and probably want to cook again. I believe that shortcuts are great, but not at the expense of quality. I administer the Everyday Sous Vide and Instant Pot Love groups on Facebook. I’ve been writing about food for a few decades and have started collecting the good stuff at https://counter.kitchen. If you buy something from one of the links, I probably get a small commission which won’t even come close to defraying the amount of money I’ve spent on these things over the years but which will make me happy anyway.
I hate food waste and I’m constantly looking for opportunities to avoid throwing away food. Also see my earlier piece on kitchen cycles for ideas about using food in stages.
Overview
The most common piece of food safety advice is “only keep food in the danger zone (40F–140F) for max four hours cumulative”, but that’s a very conservative guideline (the rules for restaurants and commercial food are intentionally very conservative, because they have the potential to sicken a lot of people all at once), and it doesn’t tell you much about all of the stuff surrounding that.
The most important thing to understand here is that this is about risk probability. Safety guidelines are not set in stone, they’re there to provide a backstop against what is *likely* to happen if you ignore them. But if you go against the guidelines, even if you do it a lot, and suffer no adverse consequences, that *DOES NOT* mean the guidelines are bad, and it doesn’t mean you’re not rolling the dice every time (though you may not be).
About Food Risks
There are a few major risks regarding food:
- Spoilage — this will make the food unappealing to eat, but generally won’t by itself make you sick. However, the conditions that lead to spoilage usually lend themselves to other problems.
- Pathogens — microbes that cause sickness. These are typically bacteria and molds, and different pathogens will colonize and thrive on different foods, in different conditions. Some microbes are beneficial and some are even delicious. Fermentation is the process of selecting for beneficial microbes and inhibiting the pathogenic ones. The most common pathogenic bacteria include E.coli, Campylobacter, Salmonella, Botulism, Listeria, and Bacillus cereus.
- Parasites — other organisms that may infect food, and then may infect you and/or produce toxins to make you sick. Probably the most common one is parasitic worms infecting fish.
- Poisons — fugu, some mushrooms, kidney beans. Some poisons can be inactivated with proper preparation, some are best avoided.
Generally we’ve done a pretty good job of reducing the presence of parasites and poisons in the food supply, but pathogenic contamination is still comparatively common, and some agents are widely present in the environment and may develop if left unchecked.
Reducing Risk
For the most part, food-related microbes have a range profile they require, consisting of five common factors, any of which being outside the range will inhibit growth, or kill them: 1) acidity, 2) temperature, 3) oxygen, 4) salt, and 5) hydration, so most common food preservation and safety measures revolve around one of these factors (e.g. canning/sterilization, fermentation, dehydration, refrigeration, vacuum packing, etc…)
In order for food to grow pathogens, pathogens must be present in the first place, and the conditions for growth must be favorable. If neither of those things are true, the food will be safe to eat. Not all food is contaminated with pathogens, but there are a lot of them, and some of them are very common, but you don’t really have any way to tell and can’t do a lot to control that. What you *can* control is the favorable conditions for growth, which are relevant *IF* there are pathogens present, and you can preserve foods in ways that minimize and/or kill any pathogens that are present already (pasteurization / sterilization).
Again, tthe guidelines aren’t there to say “if you leave food out for more than 2–4 hours it will turn instantly poison”. They are there to decrease *risk* in the case where pathogens are present and conditions are favorable for growth. Moreover, spoilage bacteria aren’t the same as pathogens but they tend to grow in the same conditions, so “it smells and tastes fine” can be a marker but isn’t a guarantee that the food isn’t contaminated with something that can make you sick.
It’s all a numbers game, and you can take more or fewer precautions, but there’s no way to know for sure if your actions helped or were excessive until afterwards.
Common Techniques
Room Temperature Storage / Dark, Cool, Airtight
A broad strokes rule is that most things that are relatively dry or still in their original packaging and sold at room temp can be stored that way for some period of time. Some underripe fruits can be ripened on the counter. Most dry foods will last longer if they’re kept away from air/oxygen, moisture, and excessive light.
Examples:
- Flours (with the exception of whole grain flours which should be stored in the freezer after opening)
- Spices
- Crackers / Cookies
- Cereals
- Fruits ripened at room temp
Refrigeration
Anything that is mostly water without any other inhibitive properties should likely be kept refrigerated. This is probably the food preservation method you’re most familiar with. Refrigerated foods have a varied lifespan dependent on a lot of factors, and I won’t get into that here except to say that most food stored in the refrigerator will typically spoil (rot, smell bad, develop mold) before it becomes dangerous. Various kinds of preservatives can of course affect that.
Examples:
- Ripe fruits
- Vegetables
- Herbs
- Dairy
- Eggs
- Meat
- Leftovers
Vacuum Packing:
As a rule, vacuum packing does not change how food needs to be stored, it only extends the length of time it can be stored that way. If food needs to be refrigerated, it still needs to be refrigerated after vacuum packing. Vacuum packing is great, and safe if done properly, but may raise some unusual safety issues related to anaerobic environments. See my separate post about sous vide safety concerns for more on that, and also my post about chamber vacs. It’s common to vacuum pack foods prior to storing in the fridge (longer than non-vacuum packed but still not very long) or freezer (very long). If I’m prepping food for the freezer I may pre-freeze it first if I want it to keep its shape or portion it out for easy access, then vacuum pack and return to the freezer. Freezer vacuum bags can easily be opened and re-sealed.
Freezing
As long as food is kept frozen, it will be safe to eat for a very long time (years), but the quality may deteriorate. Vacuum packing will dramatically extend the quality life of frozen food by preventing moisture loss and crystalization (freezer burn). Freezing does not kill a significant number of pathogens, it only inactivates them for the time while they are frozen. Freezing will kill most parasites, so it’s a common way to sterilize fish (if done for sufficient time at a low enough temperature).
Examples:
- Fresh berries, frozen in an individual layer on a sheet pan lined with parchment paper for a day or so, then vacuum sealed into bags. Used for pancakes, muffins, compote, quick jams, pastries (clafoutis).
- Orange and grapefruit juices, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags. Used for sauces and cocktails.
- Orange juice concentrate, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for sauces and cocktails.
- Egg whites, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for sauces and cocktails.
- Fresh squeezed lemon juice in 1-cup aliquots, in a plastic jar or vacuum bag, used for making lemonade.
- Ginger juice, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for making ginger beer.
- Chopped parsley in water, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for finishing coleslaw and mixing into cheese fillings.
- Chopped parsley in oil, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for finishing pasta, potatoes, and other starches.
- Chopped parsley in butter (whipped in the food processor), in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for finishing pasta, potatoes, and other starches.
- Chopped cilantro in oil, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for guacamole, marinated chicken quesadillas, and the like.
- Yogurt starter, in 1–2 tbsp cubes in an ice cube tray, then vacuum sealed into bags, used for making homemade yogurt.
- Butter, I buy in 5-pound bricks, break it up into 1-pound chunks, vacuum pack, and freeze.
Fermenting
Fermenting is the process of encouraging beneficial microbes to grow on food, to create an environment in which pathogenic and spoilage microbes can’t grow. Often fermented foods are left at room temperature until “ready”, then stored longterm in the refrigerator to slow the fermentation and preserve quality, but many of these techniques are commonly used in places where refrigeration isn’t available (or were developed before refrigeration was invented). Fermentation is a wide and varied field. See my posts about fermented pickles, ginger beer, and yogurt.
Examples:
- Cucumbers, dill, garlic -> dill pickles + garlic paste
- Cabbage -> sauerkraut or kimchi
- Milk -> kefir, yogurt
- Beer
- Wine
- Soft drinks
- Some sausages
Dehydration
Dehydration is the process of removing water from food to the point where most pathogenic and spoilage microbes can’t grow, but usually leaving a bit of water in for texture. The amount of preservation you get out of it is related to how much water you remove. A dehydrator appliance is usually the easiest way to do this, but some air fryers / convection ovens may have low enough temperature settings for this. You typically do not want to “cook” the food as it’s commonly understood, but you want to use a high enough temperature to inhibit microbe growth while the food is drying. Freeze drying is a form of dehydration that removes almost all of the moisture, but it’s not common in home settings as the equipment to do this is very expensive.
Examples:
- Grapes/Raisins
- Apple slices
- Mango slices
- Beef jerky
Cooking / Pasteurization / Sous Vide
It’s not commonly thought of as a food preservation technique, but cooking food in general definitely will extend its life and make it safer to eat. Sous vide pasteurization is often used to allow foods to be stored for longer in the fridge (up to 90 days if properly handled and chilled), and foods can be held sous vide at 130F for long periods of time safely (though the quality may suffer). Read more in my summary of sous vide safety issues.
Canning
Canning is the process of sealing food, usually in jars, so it can be stored shelf stable at room temperature. See my Intro to Home Canning.
Boiling water canning
Foods that have a high acid level may be safely canned with boiling water.
Examples:
- Fruit jellies and jams
- Applesauce
- Corn relish
- Maple syrup
Pressure canning
Foods that are low-acid must be canned in a pressure canner, to raise the temperature high enough to kill botulism spores.
Examples:
- Tomato sauce (marinara, meatsauce)
- Whole tomatoes / grape tomatoes
Curing
Curing is preparing food with an excess of salt (either regular sodium chloride or curing salts or some combination) to inhibit microbe growth. It is often combined with smoking for additional flavor.
Examples:
- Lox / gravlax
- Some sausages
- Bacon
Composting
When all else fails, I urge you to support your local composting initiatives rather than throwing unused food in the trash.
I’m continually thinking of ways to make food last longer, but also transform it using these techniques to maximize the flavors and textures, and I hope this inspires you to do the same.
Feedback is welcomed! Leave a comment here, or find me @fields@hachyderm.io on mastodon or @unsellingconvenience on instagram. If you found this helpful, check out my other writing about food and home cooking at counter.kitchen.
