Is a Plastic Knife a Substitute for Vacuum-Packing Lettuce?

plastic knife.jpg

Hearts of Romaine chopped with a plastic knife.

I love commenters!  They make blogging fun and educational. They also give me ideas for future experiments and posts.

In regard to “Salad in a Jar,” several people have left comments suggesting the use of a plastic knife to cut lettuce. They claim it deters brown cut edges, thus avoiding the need to vacuum-pack lettuce for those who desire to store cut lettuce long term.  When I say long-term, I’m talking about at least a week or even longer.

Is it true?  Could a plastic knife make vacuum-packing lettuce unnecessary? I decided to test it for myself, so I chopped some hearts of Romaine with a plastic knife and some with a metal knife.

plastic knife-3.jpg

Hearts of Romaine chopped with a metal knife

I prepared three jars.  The first was filled with lettuce cut with a plastic knife, stored in a securely-covered glass jar, but not vacuum-packed. The second contained lettuce sliced with a plastic knife, then vacuum-packed. The third jar was prepared the usual way I always do it–hearts of Romaine lettuce, swiftly chopped with a metal knife and then vacuum-packed.

plastic knife-5.jpg

All jars of lettuce were stored in the refrigerator.

I put these prepared jars in the refrigerator Sunday afternoon.

key lime pie and plastic knife experiment-22.jpg

Ready to eat salad?

The following Friday, I opened them to see the results.

key lime pie and plastic knife experiment-24.jpg

After 6 days, which lettuce would you choose?

Interesting, don’t you think?  The two jars that were vacuum-packed, both the one cut with a metal knife and one cut with a plastic knife, still look as fresh as the day I packed them. No brown edges. But that jar on the left, cut with a plastic knife, but not vacuum-packed?  Yuk!!

Looks like I won’t be needing my plastic knife after all since a sharp metal knife cuts faster and easier.  Vacuum-packing removes the oxygen so the edges don’t get brown no matter how you cut the lettuce.

Related Posts:

Salad in a Jar

Salad Fixins

The Lettuce Experiment

How to Make Salad in a Jar That Lasts a Week–a Video and FAQ

Which Vacuum-Pack Machine Should I Buy to Make Salad in a Jar?

Yes, You Can Use a Handheld Vacuum-Pack Machine to Seal Salad in a Jar

Can I Add Other Foods to My Vacuum-Packed Jar of Lettuce? 

Email This Post Email This Post Share Follow me on Pinterest
Dove December 28, 2014 at 11:49 pm

Honestly, this is way to much work. I just cut up my lettuce. Throw it in a big Tupperware bowl. Place several paper towels on top. Put the lid on the bowl. And then flip upside down and leave it like that in the fridge. Cucumbers, carrots, and all in the same bowl. It lasts at least a week like that. As long as you don’t put it in the coldest part of your fridge. I do the same in smaller portions, in cheap Tupperware. Like 4 containers for $1. Give it a shot 🙂 oh I also just pat the lettuce dry. I don’t have a spinner.

Dana January 6, 2014 at 4:18 pm

I remember seeing this concept floating around fb a while ago, but the person demonstrating the technique gave a non-vaccum sealer option for those of us who don’t have, nor wil we buy, a vaccum sealer. Have you ever seen/tried it?

Paula January 7, 2014 at 7:09 am

Hi Dana,
I’m not sure what you are talking about. You can always put lettuce in a quart jar without sealing it but it won’t last as long in my experience. However, there are several ways to get a vacuum seal besides using a full-size vacuum machine. See this post and this post.

Ray August 6, 2013 at 5:26 am

Hi, Paula. Firstly, please ignore my email. It was made by a friend in the 6th grade. Secondly, I have been following your blog for a while now, and I love that salads are kept fresh in a vacuum-sealed canning jar! I read of all the comments above and I am so excited to finally try my own salads in a jar, but because I like spinach and a lot of leafy greens in my salads, I am still hesitant to try it out. I was looking at this website: http://eatlocal365.com/2011/05/17/how-to-store-your-leafy-greens-to-make-them-last-longer/, and it tells me that spinach can last longer by storing it in the above mentioned way, but I was wondering if the spinach and the leafy greens are rolled up, as mentioned, and placed in a jar and vacuum-sealed, would that help keep the spinach fresh longer? You say you only carry it in the jars and eat in a bowl anyway, so if I were to roll it up (though a bit inconvenient during lunch time) and unravel the towels during lunchtime before placing it in a bowl, maybe that will keep it longer…? How long does the spinach last in a vacuum-sealed jar anyway?

Paula August 7, 2013 at 9:38 pm

Ray,
Spinach is too delicate for vacuum-packing. At least, that’s my experience.

Helene June 13, 2013 at 4:43 pm

i definitely see a difference btwn the plastic and metal kinfe vac packed jars of lettuce. crispier for sure with the plastic and the metal slightly browned compared to the plastic. ive never bot a plastic knife but then again i never even cut up my lettuce. will this work with bagged precut/premade lettuces?

Savannah March 3, 2013 at 9:43 pm

Where do I get one of those hand held pumps and the mason top one so I wouldn’t have to prick a hole in the top of the jar? I don’t want to invest in a food saver.

Lee October 2, 2012 at 6:17 pm

How about your prepackaging of dressing? Where can I find the instructions?

Lee October 2, 2012 at 6:17 pm

Sorry, forgot to ask if romaine is the only kind you can use for this.

Paula October 2, 2012 at 10:04 pm

Lee,
Romaine is the best in my experience. Radicchio is good too. I like them mixed. More tender lettuce does not do well and Spinach doesn’t last at all.

You can read about the way I do my dressing here.

Paula Billingsley July 11, 2012 at 5:22 pm

I canned about 8 jars of lettuce, what a great idea. I was throwing so much out and I even packed spinach too. I can vac pack more things too.
ThanksFor the idea
Paula Billingsley

Darris June 27, 2012 at 1:52 am

Thanks for the link to your steel knife vs. plastic knife Paula . . . just saved me $40! I watched a video using the jar attachment and using a vacuum cleaner. It sealed the lids perfectly! This excites me to no end as I really didn’t want another gadget AND I REALLY didn’t want to use plastic bags. Have you seen, or used, the vacuum cleaner method? Sounds a bit hokey but heh, if it works I’m on it!

Melissa May 29, 2012 at 8:07 am

Well that solves that! Thanks for the experiment. Proves you can’t believe everything you hear…

Erin May 14, 2012 at 3:49 pm

Ok…I don’t know how to vacuum pack in those jars? How do I do that and then get the lid on?

Paula May 15, 2012 at 3:10 pm

Erin, you need an attachment. You can see all the details and pictures here.

Sandra April 21, 2012 at 4:42 pm

My husband suggested putting the lettuce in a vacuumed packed canister since it didn’t last more than 3-4 days in the frig. I was still able to make a salad after 2 weeks…To be honest I thought he was crazy. Lol

Paula April 21, 2012 at 5:16 pm

Hi Sandra,
Same principle as salad in a jar. Although I have had nothing but trouble with those canisters. They all crack, and pretty quickly too. Not you?

Nicki Woodard April 21, 2012 at 12:02 pm

The hose that connects the lid to the sealer, can you just use a plastic hose from the hardware store, or does it need the little “flag” tab on each end? I just got my lid sealers from Cabela’s today.

Paula April 21, 2012 at 5:17 pm

Nicki,
I have never tried it. Not optimistic it will work but let me know if you do, and it does. I have another idea. Just buy a 4-dollar ZipLock hand pump. Then you don’t need the hose. Just place it on top of the hole of the wide-mouth attachment and pump away. It works (unless you get one that has a crack in it like the first one I bought).

SweetCarol April 19, 2012 at 3:28 pm

Thanks for the experiment. Now I wonder about just putting the lettuce in the vacuum packed “bag” as that would take less space and there is nothing to break in case it falls. Is the purpose to eat the salad out of the jar?Does it squosh the veggies in a bag. mY DAUGHTER’Svacuum packer has special jars, a big one and a small one with special lids. They are a hard plastic not glass so not as likely to break. Not sure of the plastic though as to BPA. I might have to get me another one. I had a good one and then moved and think it went to a shed that we ended up0 selling off. Got a cheaper one and it isn’t worth the money. Think it will be worth getting another one. Maybe Costco will have a good one for a better price. Could join sprout people blog and have added greens, living greens for your salads, too.

Paula April 20, 2012 at 2:51 pm

Carol,
One reason I like using jars is because my lettuce is not crushed like it would be with a bag. Also, the bags are expensive. Can’t imagine using a bag every day. YIKES!
The special containers sold with FoodSaver Vacuum systems have not worked out for me. Every single one of them as cracked, soon after I got it. Which means it will not hold a seal. They are only good for vacuum packing a smaller jar inside.
I hope you’ve seen my posts about using the portable vacuum sealers. They are much less expensive. You can even use the hand pump sealer sold by Ziplock but no matter what you use, you must have the large-mouth jar attachment. Thanks for writing.

Karen April 18, 2012 at 9:58 pm

I’ve always wondered about the plastic knives. So glad you did this experiment and shared it with us. I’ve never been big on salads for lunch, but my husband eats them all the time. And now that he’s home full time, he makes them for both of us and I love it! I guess I always thought it would be too much work. I think I need to treat us to one of the vacuum packs. It would be a lot easier for him to make my salad:)

Paula April 18, 2012 at 10:42 pm

Karen,
I’m rather envious that your husband makes lunch everyday. How nice!

Faye April 18, 2012 at 9:08 pm

I haven’t used my vacuum-pack for years. Thank you for a reason to get it out and use it. I look forward to non-rusty lettuce.

Paula April 18, 2012 at 10:41 pm

Faye,
I think a lot of people have one of those machines stuck back in the corner of their cabinet. I had mine for some time before I figured this out.

Mid Mod Tom April 16, 2012 at 11:38 am

Great experiement!

Megan's Cookin' April 16, 2012 at 8:47 am

This just goes to prove that I need that vacuum thinking at Target! I was just thinking about that the other day too. I’m such a procrastinator!

Procrastibaker April 16, 2012 at 2:52 am

What’s insanely cool about this phenomenon is that it can be explained really easily by a process called Enzymatic Browning. This occurs in many fruits and vegetables.

The cutting of the lettuce causes physical damage to it by rupturing the cells that make it up, releasing the substances that were previously separated inside the cell. There are chemical compounds, nutrients and enzymes that are now free to react with one another.

In the presence of oxygen, a certain enzyme (phenolase) catalyses one step in the biochemical conversion of phenolic compounds to form brown pigments known as melanins. This is why, as you saw, vacuum sealing lettuce reduces browning. Phenolase can’t oxidise the phenols without oxygen being present.

The presence of iron or copper can increase the rate of reaction. This can be easily observed when lettuce is cut with a knife that has lost its outer coating and has rusted. So plastic is better in this case!

Saying that, the choice of knife material really doesn’t make too much of a difference, as the metal ions only increase the rate of reaction ever so slightly. What’s really important is keeping the enzymes inactive. This can be done using high temperatures (blowtorch), low temperatures (fridge but NEVER freezer), acidic conditions (add citric acid) or, as you found out, anaerobic conditions (jarring or vacuum sealing).

And…that’s the science!

Paula April 17, 2012 at 7:40 am

Hi Procrasti Baker,

I loved reading your comment. Thanks for taking the time to write all that. Looks like I was right about the different kinds of knives. I just wasn’t quite sure why. I have tried rinsing the lettuce with lemon juice but the results couldn’t compare with vacuum-packed lettuce. Paula

KarenDF October 29, 2012 at 11:48 am

Procrastibaker, I LOVE the science of it all … thanks for sharing this. Your name is adorable … it’s the perfect description of me this month since I’ve been meaning to bake my favorite sweet breads this month! I am officially reminded & inspired to procrastinate no more!

Deborah April 15, 2012 at 9:41 pm

Paula, I’m sure you’ve heard this before, but you are a genius!!! Nobody else has mentioned this fabulous idea. I have thrown out so much prepared lettuce due to browning, it isn’t funny. I love you!!! Thanks for sharing.

Paula April 17, 2012 at 7:42 am

Thanks Deborah,
Few people have ever referred to me as a genius so I’m going to savor your nice words. Paula

sarah April 15, 2012 at 12:13 pm

Love when you do things like this!!! I am soooo grateful for this blog!!!!!

Ann Baker April 15, 2012 at 10:21 am

Interesting experiment, Paula. I would add that the plastic lettuce knives are terrific for teaching young children knife skills. They can safely chop soft fruits and vegetables without risk of injury. Haven’t jumped on the vacuum-seal bandwagon yet, but those results are definitely moving me in that direction!

Paula April 15, 2012 at 1:26 pm

Ann,
Your comment perfectly illustrates why I love comments. I didn’t even think about children using plastic knives but that is a great idea. Glad I haven’t given mine away yet. I am saving it for the next time my grandson wants to cook alongside me. Thanks so much for writing.

Vicki April 15, 2012 at 8:52 am

Question? The jars shown are standard canning jars with lids. What tool or how do you vacuum standard canning jars without using heat?

Paula April 15, 2012 at 1:44 pm

Hi Vicki, You are correct that these are standard canning jars. You can read all about storing chopped lettuce in quart Mason jars here.

TheKitchenWitch April 15, 2012 at 8:52 am

Oooh, Paula did a science experiment! How cool is that?

Meredith G. April 15, 2012 at 8:41 am

Interesting. But now the next question would be, are there different types of metal that would make different results? Any how about ceramic knifes? Inquiring minds want to know.

Paula April 15, 2012 at 1:41 pm

Meredith,
The answer to your question is pretty simple…I think. It doesn’t really matter how you cut the lettuce, whether it is a plastic knife, a regular stainless, ceramic or just tear it with your hands. The key to brownless edges is storing it in an oxygen-free environment by vacuum-packing it in a quart jar. If you haven’t tried it, you will be amazed.

Rita April 15, 2012 at 8:35 am

My Food Saver is on my counter and I use it all the time, but I have never heard of vacuum sealing lettuce in a jar; I am in awe and ca’t wait to try this.(forget the plastic knife).Happy I found you!
Rita

Lorraine April 15, 2012 at 6:18 am

Can’t get clearer than that! Thank you for the demonstration.

Laura April 14, 2012 at 11:05 pm

Thanks for that! Vaccum packed salad has saved me money already, and I just started doing it about a month ago.

Paula April 15, 2012 at 7:16 am

Hi Laura,
Glad to hear it has saved you money. Hopefully, inspired you to eat more salad, too.

Betty @ scrambled hen fruit April 14, 2012 at 9:57 pm

I just found a wide-mouth jar sealing attachment at the thrift store I frequent…Yay! I’m going to try it out with lunch salads for the week. 🙂

Paula April 15, 2012 at 7:15 am

Betty,
Lucky for you! Hope you like it.

leslie@heart4home.net April 14, 2012 at 9:55 pm

Thanks so much for showing us your test/results. It’s amazing how well the vacuum-packed lettuce does! I love your Salad-in-a-Jar idea and share it with ALL my family and friends. 🙂

Paula April 15, 2012 at 7:14 am

Thanks for writing Leslie. And thanks for sharing with your friends too.

Comments on this entry are closed.

Previous post:

Next post: