Having extra frozen produce on hand can be a huge benefit to the chef on-the-go: for smoothies in the morning, for quick veggie stir-fry’s at night, for whatever! And freezing extra food is so easy, you just pop it in the freezer and hope all goes well, right? Wrong! Unfortunately, there’s a right way to freeze food and a wrong way to freeze food, and the right way is called “flash freezing.”
So what is flash freezing? Put simply, flash freezing is freezing something immediately, so that the cellular structure of that food item (most often produce) remains intact. In a commercial setting, flash freezing is often achieved by using an air tunnel: food in the tunnel is blasted with air set to -40 degrees Fahrenheit. Food might also be dropped into a liquid halocarbon (a type of FDA-approved liquid for flash-freezing “en mass”). The cost of these methods is incredibly high, and the volume of materials required is significant, so ultimately these are not efficient methodologies for flash freezing in the home. But never fear! There are ways to flash freeze just the right amount of produce in your home quickly, easily, and efficiently.
The key to flash freezing in the home is ensuring your food has maximum contact with cold air using one of two methods.
Method one, the “easy way”:
- Put your food on a cookie or baking sheet that’s covered in parchment paper (or a re-usable silicone mat) to prevent sticking.
- Make sure you spread your food out so that nothing is touching anything else (1/8 inch between everything, minimum).
- Put the baking sheet in your freezer as close to the fan as you can get it so that the fan is blowing directly onto the food (look for the vents near the top of your freezer).
- Wait 20-30 minutes.
- Pull the food out and place it directly into a storage container, eliminating as much air as possible (so vacuum-packed mason jars or vacuum-sealed bags work best). Do this as quickly as possible to reduce possibility of thaw.
- Put your packed food back in the freezer, and start the process over with the next batch!
If you go with method one, do keep one thing in mind: while you can’t really “over freeze” something by leaving it in the freezer, the maximum amount of time recommended to leave a fruit or vegetable unsealed in the freezer is about 40 minutes. Much longer than that and the humidity in the air will start to crystalize on your food (“freezer burn”), and will simultaneously pull water out of food, starting to dehydrate it. It’s not hugely problematic if this happens, but ultimately will just render the food less tasty. Because of how the structure of the cells works, the hardier a food item is, the longer it can (or potentially should) stay in the freezer, so while raspberries really shouldn’t be left for longer than about 20 minutes, bacon can remain in the freezer for over an hour without any effect on the flavor. There’s no hard or fast rule for how long to flash freeze things (although 20-30 minutes is a safe bet): you may just have to play around with timing as you try your hand at flash freezing different food items.
Method two, the “hard way”:
This methodology will simulate the air tunnel method used in commercial flash freezing.
- Find two foam coolers that will “nest” (a small one that will fit inside a bigger one), and make sure the outside of the smaller cooler is at least three inches away from the inside of the larger one.
- Get one small, cheap hand-held fan or desk fan that’s as thin as possible (more than two-inches wide is too thick).
- Cut a fan-sized hole in the wall of the inside cooler, plug in your fan, turn it on, and rest it inside the hole facing inwards toward the center of the inside cooler (if your fan has a cord, it can trail up and out of the outer cooler).
- Get dry ice from your local grocery store. Be very careful with the dry ice as it will burn you on contact. Use silicone oven mitts and tongs when handling the ice.
- Your dry ice will come in large blocks: chip away some smaller shards or ice and place them in both coolers so that the bottom inch of both is filled.
- Let your fan run in the ice for a good 15 minutes – things will start to get very, very cold.
- put your food on a small cookie or baking sheet, again using parchment paper or a silicone mat to prevent against sticking, and making sure that no food is touching.
- Place the pan on the ice in the inner cooler, with the fan continuing to blow. Let it sit for 15-25 minutes this way.
- Remove the food from the coolers and place directly into storage containers (again, with the goal of sealing out air using either vacuum-packed mason jars or air-tight bags). Then put these containers into the freezer.
Method two is admittedly a bit more involved and high-tech, so you might be asking yourself, “why bother?” While method one is perfectly fine for flash freezing in the home, method two does produce better results, and here’s why: the dry ice used in the freezing process will drive away any and all humidity, and will get your food much colder much faster. Method one will do a pretty decent job of freezing your food quickly and retaining cellular structure of the nutrients, but method two will do it exceptionally well. So it’s up to you: if you’re aiming for greatness, go with method two, but if simplicity is more your style, method one will work just fine.
Home Flash Freezing
For some, this may sound like a lot of work just to freeze some extra produce. Is it really necessary to go through this whole “flash freezing” process? Unfortunately, there is a good reason to go the extra mile with your excess produce. Freezing food at a normal rate (without attempting to flash freeze), isn’t necessarily bad for you: in fact, it’s fine. But here’s what will happen: food brought from a higher temperature to a lower temperature at a slow rate will mean different parts of the food will freeze at different rates, causing different areas of the food to expand or contract at different rates (depending on how much water there is), and making the liquid in the cells of the food crystalize, puncturing the cell walls and creating a total mess of the cell structure of the food. When the cellular structure of your food is damaged, the texture and flavors of the food begin to deteriorate. On the other hand, flash freezing will freeze all parts of the food at once and not change the chemical composition, because there won’t be time for any parts of the food to expand, and very little time for crystallization. So the texture of the food will remain as it should be and the flavor will not be jeopardized. So yes, flash freezing does take a little extra work and attention to detail. But your end product will be as tasty, nutritious and delicious as it was on day one, so we think the extra work is worth it.