Strawberries - Keeping Fresh Longer in Fridge

[MickinMD ★]

I bought strawberries to go with Cheerios and followed instructions about making them stay fresh longer in a vacuum bag. I put them in one of the Sous Vide vacuum bags I have, and pumped the air out, making sure not to have the bag pressing too tight on the berries, and refrigerated them.

Then, I looked on YouTube and i saw another way to make strawberries last in the fridge “almost two weeks:” 

The method is to soak them in a vinegar (white distilled, but probably any kind is ok) and water solution (as dilute as 1/4 cup vinegar and 2 1/2 cups water) for 2 to 15 minutes (kills potential mold, and bacteria and removes some pesticides), some say rinse with cold water (the video below says don’t bother), pat them dry with paper towels and store them in a container in the fridge, separating layers of strawberries with paper towels.

The 15 minutes probably stems from an NIH Study (https://pubmed.ncbi.nlm.nih.gov/15698693/) that studied vinegar, lemon juice, and a 1:1 mixture for up to 60 minutes and found that salmonella was undetectable in salad veggies infected with it after 15 minutes.

But many YouTube videos (and the comments that go with them) say that 2-3 minutes works and makes the berries last up to 2 weeks. I’m going to try that first..

 

The videos widely varied the volume ratio of vinegar to water, but I did chemistry pH calculations (at bottom for those interested) and found that 1 part vinegar added to 10 parts water only raises the pH of vinegar from 2.4 to 2.9, which is still plenty acidic and close enough to the NIH study to work.

 

Here's a good video on treating strawberries with vinegar (it used white distilled, but apple cider, pineapple, etc. Should be fine), it uses 5 cups water to 1/2 cup (though I’ll cut water and vinegar in half and use a bowl, not the sink, if that will cover my much smaller amount of strawberries):

 

This vid. uses paper towels - some vids use one for each layer of stored strawberries:

A vinegar bath, drying, then vacuum storing in the fridge in the Sous Vide vacuum bags should make the berries last longer - though up to 2 weeks with the vinegar alone is surely enough!

pH Calculations

pH is a measure of H30+ concentration where 7 is neutral (like pure water), under 7 is acidic and over 7 is basic. Each unit represents a factor of 10, so a pH of 5 is 10x as acidic as a pH of 6, a pH of 4 is 100x as acidic as a pH of 6, etc.

White distilled vinegar is essentially 5% acetic acid in water and has a listed pH of 2.4. Apple Cider Vinegar and other vinegars have additional organic compounds that very slightly raise the pH, but all can be treated as being roughly at a pH of 2.4

Acetic Acid ionizes in water as CH3COOH + H2O --> CH3COO- + H3O+, where H3O+ is the “acid” ion that pH measures.

But, unlike strong acids like hydrochloric or sulfuric that ionize completely, only a very tiny fraction of Acetic Acid ionizes to form H3O+ and it has an "equilibrium constant," Ka, of 1.76 x 10^-5 where:

Ka = [CH3COO-][H3O+]/[CH3COOH] where the brackets mean "concentration" and since [CH3COO-] = [H3O+]

Ka = [H3O+]^2/[CH3COOH] which rearranged is:

[H3O+] = SQR(Ka x [CH3COOH]) and since the molecular weight of CH3COOH is 60 and since a 5% solution means 50 grams/liter and pH is the -log of the concentration of H3O+:

pH = -log [H3O+] = -log (SQR(Ka x [CH3COOH])) = -log (SQR(1.76 x 10^-5 x 50/60)) = 2.417

This calculation matches the listed pH of 2.4 of distilled white vinegar.

So the calculation was done right.  The next step is to see what happens when vinegar is diluted.

3 parts water, 1 part vinegar changes the 50 in the pH equation to 50/4 and 10 parts water, 1 part vinegar changes it to 50/11, etc. The calculations become:

3 parts water, 1 part vinegar, pH = 2.718

7 parts water, 1 part vinegar, pH = 2.868

10 parts water, 1 part vinegar, pH = 2.938

So there's no reason to use 1/2 cup of vinegar with 1 1/2 cups of water as some videos instruct. I/4 cup to 2 1/2 cups of water is close enough to the same acidity that it should work fine, saving on the use of vinegar.

[Longjohn ★]

The best way to keep strawberries fresh is to eat them all the first day and buy more tomorrow.

[Kzoo]

47 minutes ago, Longjohn said:

The best way to keep strawberries fresh is to eat them all the first day and buy more tomorrow.

Beat me to it.  Who wants to store strawberries?  Buy 'em, eat 'em, buy more, eat more...........

Eat 'em or freeze 'em

[Dirtyhip]

Just eat them.  They are best the first of second day.  

I do like your vinegar idea though.  Thank you for helping enlighten us with your chemistry stuff.

[ChrisL]

Strawberries are dirt cheap out here when in season.   We buy them by the flat and toss those that go bad. Then get another flat...

[MickinMD ★]

1 hour ago, ChrisL said:

Strawberries are dirt cheap out here when in season.   We buy them by the flat and toss those that go bad. Then get another flat...

Wish they were cheap here!  The other thing is I hate eating a few and then seeing the rest get moldy if I go a few days between eating them.  I like them best with Cheerios but tend to use blueberries and bananas because they keep better.

[Kzoo]

56 minutes ago, MickinMD said:

The other thing is I hate eating a few

Me too.  So eat more.

 

[Ralphie ★]

I’ll have to try that, because we also eat them just a few at a time. Thanks for running the numbers, dr mickin!

[12string]

2 weeks?  They don't last 2 days around here!

The strawberry patch is about done for the year, as of yesterday.  I planted a variety that was developed for eating immediately, can't be stored or shipped.  But they are prolific, and packed with intense flavor.  I did freeze a couple gallons for use later, but the munching berries are done.

[ChrisL]

1 hour ago, MickinMD said:

Wish they were cheap here!  The other thing is I hate eating a few and then seeing the rest get moldy if I go a few days between eating them.  I like them best with Cheerios but tend to use blueberries and bananas because they keep better.

Most of the strawberries we eat are locally grown, like less than 10 miles from me.  

The clear zone for the North end of the closed MCAS El Toro is a huge strawberry field right now. Most of the base has been developed but this area is still undeveloped so is being used for seasonal crops.  

[Dottleshead ★]

12 hours ago, Longjohn said:

The best way to keep strawberries fresh is to eat them all the first day and buy more tomorrow.

1000000000000000000000000000000%

[Ralphie ★]

13 hours ago, MickinMD said:

tend to use blueberries and bananas because they keep better

Blueberries are perfect because not only do they last a long time, they don't require any cutting.  Wash and wear - eat!  Same advantage as a Boston Terrorist in the dog world - no grooming required!

[Airehead]

buy some and immediately freeze some for January eating.  Finish the rest and buy more-- repeat the cycle.  This way you are always eating fresh and you have a wonderful winter treat.

[Parsnip Totin Jack ★]

Anyone else glad we got out of that lesson without any assigned homework?

[Ralphie ★]

3 minutes ago, Old No. 7 said:

Anyone else glad we got out of that lesson without any assigned homework?

It got a little deep there for a while, and I am a chemical engineer!  

 

[MickinMD ★]

7 hours ago, RalphWaldoMooseworth said:

It got a little deep there for a while, and I am a chemical engineer!  

 

I'm also glad it didn't go any deeper. I've been out of chemistry long enough I had to think a minute to remember the word "buffer."

Like looking in the back of the math book to see the answers before you work the problem, I looked up vinegar's pH to make sure I was setting up that equilibrium equation calculation right.

[Airehead]

10 hours ago, Old No. 7 said:

Anyone else glad we got out of that lesson without any assigned homework?

He is the type of teacher who will assign homework on Friday. 

[Airehead]

On 6/18/2020 at 12:01 PM, MickinMD said:

I bought strawberries to go with Cheerios and followed instructions about making them stay fresh longer in a vacuum bag. I put them in one of the Sous Vide vacuum bags I have, and pumped the air out, making sure not to have the bag pressing too tight on the berries, and refrigerated them.

 

Then, I looked on YouTube and i saw another way to make strawberries last in the fridge “almost two weeks:” 

 

The method is to soak them in a vinegar (white distilled, but probably any kind is ok) and water solution (as dilute as 1/4 cup vinegar and 2 1/2 cups water) for 2 to 15 minutes (kills potential mold, and bacteria and removes some pesticides), some say rinse with cold water (the video below says don’t bother), pat them dry with paper towels and store them in a container in the fridge, separating layers of strawberries with paper towels.

 

The 15 minutes probably stems from an NIH Study (https://pubmed.ncbi.nlm.nih.gov/15698693/) that studied vinegar, lemon juice, and a 1:1 mixture for up to 60 minutes and found that salmonella was undetectable in salad veggies infected with it after 15 minutes.

But many YouTube videos (and the comments that go with them) say that 2-3 minutes works and makes the berries last up to 2 weeks. I’m going to try that first..

 

 

 

The videos widely varied the volume ratio of vinegar to water, but I did chemistry pH calculations (at bottom for those interested) and found that 1 part vinegar added to 10 parts water only raises the pH of vinegar from 2.4 to 2.9, which is still plenty acidic and close enough to the NIH study to work.

 

 

 

Here's a good video on treating strawberries with vinegar (it used white distilled, but apple cider, pineapple, etc. Should be fine), it uses 5 cups water to 1/2 cup (though I’ll cut water and vinegar in half and use a bowl, not the sink, if that will cover my much smaller amount of strawberries):

 

 

 

This vid. uses paper towels - some vids use one for each layer of stored strawberries:

 

A vinegar bath, drying, then vacuum storing in the fridge in the Sous Vide vacuum bags should make the berries last longer - though up to 2 weeks with the vinegar alone is surely enough!

 

 

 

pH Calculations

 

pH is a measure of H30+ concentration where 7 is neutral (like pure water), under 7 is acidic and over 7 is basic. Each unit represents a factor of 10, so a pH of 5 is 10x as acidic as a pH of 6, a pH of 4 is 100x as acidic as a pH of 6, etc.

 

White distilled vinegar is essentially 5% acetic acid in water and has a listed pH of 2.4. Apple Cider Vinegar and other vinegars have additional organic compounds that very slightly raise the pH, but all can be treated as being roughly at a pH of 2.4

 

Acetic Acid ionizes in water as CH3COOH + H2O --> CH3COO- + H3O+, where H3O+ is the “acid” ion that pH measures.

 

But, unlike strong acids like hydrochloric or sulfuric that ionize completely, only a very tiny fraction of Acetic Acid ionizes to form H3O+ and it has an "equilibrium constant," Ka, of 1.76 x 10^-5 where:

 

Ka = [CH3COO-][H3O+]/[CH3COOH] where the brackets mean "concentration" and since [CH3COO-] = [H3O+]

 

Ka = [H3O+]^2/[CH3COOH] which rearranged is:

 

[H3O+] = SQR(Ka x [CH3COOH]) and since the molecular weight of CH3COOH is 60 and since a 5% solution means 50 grams/liter and pH is the -log of the concentration of H3O+:

 

pH = -log [H3O+] = -log (SQR(Ka x [CH3COOH])) = -log (SQR(1.76 x 10^-5 x 50/60)) = 2.417

 

This calculation matches the listed pH of 2.4 of distilled white vinegar.

 

So the calculation was done right.  The next step is to see what happens when vinegar is diluted.

 

3 parts water, 1 part vinegar changes the 50 in the pH equation to 50/4 and 10 parts water, 1 part vinegar changes it to 50/11, etc. The calculations become:

 

3 parts water, 1 part vinegar, pH = 2.718

 

7 parts water, 1 part vinegar, pH = 2.868

 

10 parts water, 1 part vinegar, pH = 2.938

 

So there's no reason to use 1/2 cup of vinegar with 1 1/2 cups of water as some videos instruct. I/4 cup to 2 1/2 cups of water is close enough to the same acidity that it should work fine, saving on the use of vinegar.

 

I read this to Mr. Aire. He nodded knowingly and asked what @MickinMD did for a living?  He is also now planning to test the strawberry longevity theory. 

[Ralphie ★]

2 minutes ago, Airehead said:

I read this to Mr. Aire.

The whole thing?!  Bless your heart.

 

[Kzoo]

43 minutes ago, RalphWaldoMooseworth said:

The whole thing?!  Bless your heart.

 

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