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Water Activity/Shelf LIfe


Sweet Impact Mama
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I've been looking into water activity (AW) and shelf life and came across some interesting formulas for estimating shelf life from the water activity of an item.

 

First a few provisos:

  1. This formula was originally developed for baked goods, in particular cakes.
  2. The formula has only been validated for AW's between 0.74-0.90
  3. The formula assumes that the items will be stored at a constant temperature. The formula below is for 21 Degrees Celsius.
  4. The formula assumes that the AW of the item does not change while in storage. 
  5. When we're talking about shelf life here, they specify Mould Free Shelf Life (MFSL). Obviously whether the product has mould or not is certainly not the only factor that would affect it's quality.

So with that all being said, I thought the results were interesting and in some cases very different from the previous examples given in the thread from Melissa Coppel and Wybauw.

 

Stored at 21 Degrees Celsius

Log10 (MFSL, days at 21°C) =7.91 - (0.081 x AW)

AW     MFSL (Days)     MFSL (Weeks)

74          82                            10.8

75          68                            9.8

76          57                            8.1

77          47                            6.7

78          39                            5.6

79          32                            4.6

80          27                            3.8

81          22                            3.2

82          19                            2.6

83          15                            2.2

84          13                            1.8

85          11                             1.5

86           9                             1.3

87           7                              1.0

88           6                              0.9

89           5                              0.7

90           4                              0.6

 

I came across it in chapter 17 on water activity and shelf life in Confectionary & Chocolate Engineering. I then found the same formula again in Bakery Food Manufacture & Quality which cited original work on this going back to the 60s which was then "robustly" validated in papers published in the 90s. A particular paper that gets cited a bit but i can't actually find seems to be where the original formulas come from. Couvain, S. P., and D. A. L. Deiler. "Equilibrium relative humidity and the shelf life of cakes." FMBRA Report 50 (1992).  

 

Obviously the best way to assess shelf life is to actually test it, but I thought it was interesting and useful so thought I'd share it. There is a webpage that has the calculator where you can select 21 or 27 Degrees C and enter your AW. It will then give you an estimate for the MFSL. https://www.dairyscience.info/newCalculators/mould.asp

 

 

Edited by DomDeFranco (log)
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3 minutes ago, pastrygirl said:

@DomDeFranco

thank you for sharing that, I’ve been wanting more detailed aw info - Wybauw gives ranges so large as to not be useful in his books 

No problem :)

 

Yeah, it's difficult finding good information on it. There are more formulas in that chapter that take into account the type of packaging and the storage environment and even the geometry of the product! But once the product is in your customers hands, it's very difficult to estimate all these conditions.

 

I'm thinking of saying that my chocolates are good for at least x amount of weeks stored between 18-21 degrees in a dry environment. Or something like that.

 

Here is an interesting graph from another article i found on Aw and shelf life at different temperatures.

Shelf life in food and water as a factor

https://www.biscuitpeople.com/magazine/post/Internal-factor-influencing-shelf-life-of-bakery-products

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@DomDeFrancothat's a very interesting chart--and quite alarming.  There is a huge difference between these figures (Aw of 85 = 11 days) and, e.g., Melissa's (3-6 weeks).  For the usual "eat within 2 weeks" directions I give customers (allowing for an additional week as they are being made and boxed), I would need to aim for an Aw not much about 80.  I just scanned my recipes, and there are only a handful that are at 80 or above (one of which, interestingly, I made today, Notter's mint ganache--but that is going into the freezer before being served at an event).  I have started emphasizing shelf life with customers.  The uncertainty in all this definitely makes one inclined more to caramels, giandujas, etc.  I have trained my one retail outlet to keep most boxes in the freezer and move them only a few at a time to refrigeration.  After that, as you say, I don't have much control over what the customer does.  Alas, one of my (and customers') favorites, pumpkin cream will need some more work.

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1 hour ago, Jim D. said:

For the usual "eat within 2 weeks" directions I give customers (allowing for an additional week as they are being made and boxed), I would need to aim for an Aw not much about 80. 

 

I'm aiming for 8-10 weeks, if 0.75 will last that long, that's exciting.  I've been trying to get things lower and lower but still pipe-able and soft to bite into, it's hard to get below 0.70.

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2 hours ago, Jim D. said:

@DomDeFrancothat's a very interesting chart--and quite alarming.  There is a huge difference between these figures (Aw of 85 = 11 days) and, e.g., Melissa's (3-6 weeks).  For the usual "eat within 2 weeks" directions I give customers (allowing for an additional week as they are being made and boxed), I would need to aim for an Aw not much about 80.  I just scanned my recipes, and there are only a handful that are at 80 or above (one of which, interestingly, I made today, Notter's mint ganache--but that is going into the freezer before being served at an event).  I have started emphasizing shelf life with customers.  The uncertainty in all this definitely makes one inclined more to caramels, giandujas, etc.  I have trained my one retail outlet to keep most boxes in the freezer and move them only a few at a time to refrigeration.  After that, as you say, I don't have much control over what the customer does.  Alas, one of my (and customers') favorites, pumpkin cream will need some more work.

Those numbers differ quite significantly from what ProChoc gives for 0.85 as well. 0.93 was 8 days on something I tested this morning. 

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8 minutes ago, Kerry Beal said:

Those numbers differ quite significantly from what ProChoc gives for 0.85 as well. 0.93 was 8 days on something I tested this morning. 

 

Are their numbers on longevity something you're able to share without violating the user agreement?  0.85 = X days/weeks, 0.80, 0.75, etc ... down to 0.60 or whatever is 'microbially stable' . 

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There doesn't seem to be much consistency in the different recommendations, that's for sure.

 

So, the pH is obviously very important as well. It could be that pro choc takes into account the pH as well as the AW?

 

And perhaps, as many ganache recipes include ingredients to lower the pH, that would explain the difference in the higher AW ratings between bakers and chocolatiers? Sorry I mean the difference in shelf life for the same AW ratings.

 

I assume there must be research done on the relationship between AW, pH and shelf life. 

 

I'll see if I get a bit of time over the weekend to look into it.

 

As an aside, I've noticed water activity meters on Alibaba for $3-400. I don't suppose anyone has any experience with them?

 

Thanks

Edited by DomDeFranco (log)
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8 hours ago, pastrygirl said:

 

Are their numbers on longevity something you're able to share without violating the user agreement?  0.85 = X days/weeks, 0.80, 0.75, etc ... down to 0.60 or whatever is 'microbially stable' . 

I’m sure I can but I’ll have to run a bunch of examples to generate the Aw numbers to get the suggested shelf life.  Shall try to find time later today 

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1 hour ago, DomDeFranco said:

There doesn't seem to be much consistency in the different recommendations, that's for sure.

 

So, the pH is obviously very important as well. It could be that pro choc takes into account the pH as well as the AW?

 

And perhaps, as many ganache recipes include ingredients to lower the pH, that would explain the difference in the higher AW ratings between bakers and chocolatiers?

 

I assume there must be research done on the relationship between AW, pH and shelf life. 

 

I'll see if I get a bit of time over the weekend to look into it.

 

As an asside, I've noticed water activity meters on Alibaba for $3-400. I don't suppose anyone has any experience with them?

 

Thanks

Not sure - I know the ingredient part does include pH for purées etc. I can see if I do water vs lemon juice and see if the Aw changes.

I’m uncertain about those cheap meters - someone needs to buy one and have it delivered to me and I’ll run it against my pAwkit and see how it compares - send back if crap - forward on if not.

 

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59 minutes ago, Kerry Beal said:

Not sure - I know the ingredient part does include pH for purées etc. I can see if I do water vs lemon juice and see if the Aw changes.

I’m uncertain about those cheap meters - someone needs to buy one and have it delivered to me and I’ll run it against my pAwkit and see how it compares - send back if crap - forward on if not.

 

Sounds like an interesting experiment. I know that if the pH is low then you can have a higher AW without it affecting the shelf life as much but i'm not exactly sure what the ranges for these things are.

 

I came across a paper that estimates the AW by using a formula using brix and pH measurements. I imagine pro-choc probably uses something like that. 

 

I'm going to buy one of those cheapo water activity meters so it would be great to see how they compare to the pAwkit ones. They still work out cheaper than a pro-choc subscription, so worth a try i guess.

 

I live in the UK though, so not sure if there would be some weird Tax rules/rates if I send it Canada and then you send it to me?

Edited by DomDeFranco (log)
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3 hours ago, Kerry Beal said:

I’m sure I can but I’ll have to run a bunch of examples to generate the Aw numbers to get the suggested shelf life.  Shall try to find time later today 

 

That would be awesome if you have time.  I bought the Rotronic handheld meter a few months ago so have the numbers, would love more info on practical application of those numbers. 

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IMG_4213.thumb.jpeg.1aac646ee8156a9171f5137b2f5b90ca.jpeg

 

 

IMG_4214.thumb.jpeg.ea61548fa1756e1ebfef6be2c601e509.jpeg

 

For the life of me - no matter how I edit in iPhoto then drag them in - they still are on their side!

 

I started with 100 grams of Callebaut 811 and 100 grams of cream - then just reduced the cream a few grams at a time to get these numbers.

 

 

Starting with 100 grams of 811 and 20 grams of water - I got 0.94. Changing to a lemon juice with a pH less than 3 brought it down to 0.92 however the lemon juice has 5% solids in it so I'm not sure it it is that or the pH that resulted in the reduction. 

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15 minutes ago, Kerry Beal said:

 

 

IMG_4213.thumb.jpeg.1aac646ee8156a9171f5137b2f5b90ca.jpeg

 

 

IMG_4214.thumb.jpeg.ea61548fa1756e1ebfef6be2c601e509.jpeg

 

For the life of me - no matter how I edit in iPhoto then drag them in - they still are on their side!

 

I started with 100 grams of Callebaut 811 and 100 grams of cream - then just reduced the cream a few grams at a time to get these numbers.

 

 

Starting with 100 grams of 811 and 20 grams of water - I got 0.94. Changing to a lemon juice with a pH less than 3 brought it down to 0.92 however the lemon juice has 5% solids in it so I'm not sure it it is that or the pH that resulted in the reduction. 

Thanks for doing this. Very interesting!

 

From what I can gather, lowering the pH does not have a significant effect on water activity. Could be the solids then?

 

The shelf lives are interesting for the basic ganache.

 

I haven't been making chocolates for very long, so it would be interesting to see what yours and others experience and gut feeling is for all these different shelf lives?

 

6 days for a 1:1 ganache seems very high to me, but I don't know? Is this at room temperature?

Edited by DomDeFranco (log)
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2 hours ago, pastrygirl said:

 

That would be awesome if you have time.  I bought the Rotronic handheld meter a few months ago so have the numbers, would love more info on practical application of those numbers. 

Could you and I do some experiments with you and your Rotronic and me and my pAwkit? Making the same thing and each testing it?

 

Did the Rotronic come with standards?

 

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40 minutes ago, DomDeFranco said:

Thanks for doing this. Very interesting!

 

From what I can gather, lowering the pH does not have a significant effect on water activity. Could be the solids then?

 

The shelf lives are interesting for the basic ganache.

 

I haven't been making chocolates for very long, so it would be interesting to see what yours and others experience and gut feeling is for all these different shelf lives?

 

6 days for a 1:1 ganache seems very high to me, but I don't know? Is this at room temperature?

Sorry - forgot to include that - yes room temperature. It does seem a little high doesn't it. 

 

K

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looks like you might  be on a Mac :

 

after your pictures appear on you post

 

drag them out on to the desktop.

 

open them 

 

rotate them

 

save 

 

delete the old rone

 

add the new one.

Edited by rotuts (log)
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5 minutes ago, rotuts said:

looks like you might  be on a Mac :

 

after your pictures appear on you post

 

drag them out on the the desktop.

 

open them 

 

rotate them

 

save 

 

delete the old rone

 

add the new one.

Thanks 

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6 hours ago, Kerry Beal said:

Could you and I do some experiments with you and your Rotronic and me and my pAwkit? Making the same thing and each testing it?

 

Did the Rotronic come with standards?

 

 

Yes and yes, but I have not calibrated it yet.

 

I usually use Felchlin and 40% fat manufacturing cream, but can get another chocolate so we have the same thing.  30% fat cream is also an option.  What chocolates do you have handy?

 

 

 

 

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28 minutes ago, pastrygirl said:

 

Yes and yes, but I have not calibrated it yet.

 

I usually use Felchlin and 40% fat manufacturing cream, but can get another chocolate so we have the same thing.  30% fat cream is also an option.  What chocolates do you have handy?

 

 

 

 

I have Belcolade and 36% cream! But nothing says we can't use water cause then the fat content isn't going to be an issue. Just trying to think what other chocolate there might be downstairs. I'm a bit challenged right now to get into my chocolate room and do things because I broke my ankle on the 4th and I'm not supposed to weight bear upon it. 

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11 minutes ago, Kerry Beal said:

I have Belcolade and 36% cream! But nothing says we can't use water cause then the fat content isn't going to be an issue. 


i do have some belcolade 70% noir supreme … and water!

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7 minutes ago, pastrygirl said:


i do have some belcolade 70% noir supreme … and water!

Mine might just be the regular garden variety belcolade. Of course we could do it with a Hershey bar or something except I think the Canadian ones are still made in Canada so might not be exactly the same. 

Edited by Kerry Beal (log)
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