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Water Activity/Shelf LIfe


Sweet Impact Mama
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If I'm trying a new filling, I will test as I make it. I will spoon out a little ganache, put it in the freezer for a few minutes and then test. That way, I can make adjustments if needed. I find the "test" improves over several days. If it is good when i make it, i know it will be good later.

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Ruth Kendrick

Chocolot
Artisan Chocolates and Toffees
www.chocolot.com

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  • 7 months later...
On 12/7/2020 at 4:31 PM, Jim D. said:

 

That should work.  If we really want to see what effect time has on Aw, I could take several samples just after the filling has been made, then put on the lids (yes, the tiny little cups come with tiny little lids) and test them over a period of days.  An after-Christmas project.

 

As @Muscadellesuggested, letting ganaches crystallize for a while might produce a different Aw reading.  I have now done that.  Today I made my new "custard ganache" with fiori di Sicilia flavoring and tested it.  To my dismay, the reading was 0.85, much higher than the numbers from my experimental batch with this filling.  This recipe was for 50% custard (cream with custard powder) and 50% white chocolate.  After a few hours had passed, it occurred to me that this was a good time to try the experiment.  And the second reading was 0.68, an amazing difference.  I had a second sample, and it produced a reading different by only 0.1.  The ganache samples had been sitting in open containers, but I can't imagine there was that much evaporation from a substance so relatively viscous, after only a few hours had passed, and in a cool space--a situation that basically emulates a ganache sitting in a shell waiting to be sealed.

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5 hours ago, Jim D. said:

 

As @Muscadellesuggested, letting ganaches crystallize for a while might produce a different Aw reading.  I have now done that.  Today I made my new "custard ganache" with fiori di Sicilia flavoring and tested it.  To my dismay, the reading was 0.85, much higher than the numbers from my experimental batch with this filling.  This recipe was for 50% custard (cream with custard powder) and 50% white chocolate.  After a few hours had passed, it occurred to me that this was a good time to try the experiment.  And the second reading was 0.68, an amazing difference.  I had a second sample, and it produced a reading different by only 0.1.  The ganache samples had been sitting in open containers, but I can't imagine there was that much evaporation from a substance so relatively viscous, after only a few hours had passed, and in a cool space--a situation that basically emulates a ganache sitting in a shell waiting to be sealed.

I've had similar experiences and have been struggling a bit to find out the best practice for measuring Aw. The fluctuations can be quite wild. I can't come up with any other explanation though than evaporation or crystallisation "locking" the moisture over the few hours it is sitting. 

Would be great to hear if anyone has better knowledge on this! Logically I'd think the best practice would be to emulate chocolates waiting to be capped, so sitting in open container the same time as in the shells, as Jim D. did. Container has much larger surface area though, not sure if it matters.

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6 hours ago, EsaK said:

I've had similar experiences and have been struggling a bit to find out the best practice for measuring Aw. The fluctuations can be quite wild. I can't come up with any other explanation though than evaporation or crystallisation "locking" the moisture over the few hours it is sitting. 

Would be great to hear if anyone has better knowledge on this! Logically I'd think the best practice would be to emulate chocolates waiting to be capped, so sitting in open container the same time as in the shells, as Jim D. did. Container has much larger surface area though, not sure if it matters.

 

Glad to hear you have also had "wild fluctuations."  Just for the record, my samples yesterday were sitting in their little testing cups, not in the bowl in which I had made the ganache, so evaporation would have been minimized.  Ordinarily I measure Aw early because it's much easier to get a sample into the cup when fluidity is at its maximum, but it had certainly never occurred to me such a change in Aw was likely, even possible.  There is a Wybauw recipe for black currant ganache that I like very much (especially paired with hazelnut gianduja), but I have avoided making it very often because of the Aw reading of 0.83 that resulted.  The ganache has always puzzled me because the ratio of chocolate+cocoa butter to liquid (which is all black currant purée) is about 2.5 to 1, thus it should not be problematic.  Next time I make this I will do the retest and see if it improves over time.  I do think leaving the test cups uncovered between readings makes the most sense because that is, as I previously stated, what happens after a filling has been deposited into a shell, but I am certainly open to corrections of my assumption (I am not a scientist, I just pretend to be one with my Aw meter).

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I have performed the experiment once more and am getting what one might call a "consistent inconsistency."  I made Wybauw's pear recipe (Fine Chocolates Gold, p. 309).  The Aw reading immediately after the ganache was piped was 0.78.  Approximately three hours later, the same sample produced a reading of 0.64.  For someone who is quite cautious about shelf life issues, these readings are very good news.

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1 minute ago, Jim D. said:

I have performed the experiment once more and am getting what one might call a "consistent inconsistency."  I made Wybauw's pear recipe (Fine Chocolates Gold, p. 309).  The Aw reading immediately after the ganache was piped was 0.78.  Approximately three hours later, the same sample produced a reading of 0.64.  For someone who is quite cautious about shelf life issues, these readings are very good news.

Thanks for posting this! I assume the temperature of the sample on both occassions was closely the same, right? 

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2 minutes ago, Jim D. said:

I have performed the experiment once more and am getting what one might call a "consistent inconsistency."  I made Wybauw's pear recipe (Fine Chocolates Gold, p. 309).  The Aw reading immediately after the ganache was piped was 0.78.  Approximately three hours later, the same sample produced a reading of 0.64.  For someone who is quite cautious about shelf life issues, these readings are very good news.

 

This is so strange. It feel like it's dropping way too much. I'm currently talking with people working with these kind of things for a project of mine. I have to ask them about this.

 

How do you store the sample for those three hours?

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4 hours ago, EsaK said:

Thanks for posting this! I assume the temperature of the sample on both occassions was closely the same, right? 

Yes, room temperature (about 70F).  The Aw meter doesn't allow a reading unless the meter and the sample are at approximately the same temp.

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4 hours ago, Rajala said:

 

This is so strange. It feel like it's dropping way too much. I'm currently talking with people working with these kind of things for a project of mine. I have to ask them about this.

 

How do you store the sample for those three hours?

 

I am leaving them uncovered.  As I said above, this is what happens when a ganache is piped into a shell that is not going to be sealed for another day, so I thought it was a quite similar situation.  Even allowing for variations in meter accuracy, there is no question readings are dropping.  Next time I'll cover the sample between readings, but I don't think this would accurately reflect what happens in real production.

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10 hours ago, Jim D. said:

 

I am leaving them uncovered.  As I said above, this is what happens when a ganache is piped into a shell that is not going to be sealed for another day, so I thought it was a quite similar situation.  Even allowing for variations in meter accuracy, there is no question readings are dropping.  Next time I'll cover the sample between readings, but I don't think this would accurately reflect what happens in real production.

 

I missed that, sorry. Yeah, but like leaving them i the open will definitely cause it to dry out a bit. Question is like how much the "dry" surface will affect any readings. Well, I'm going to talk with someone about this later, someone who's expertise is food safety. She will know more than me for sure. :D

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49 minutes ago, Rajala said:

 

I missed that, sorry. Yeah, but like leaving them i the open will definitely cause it to dry out a bit. Question is like how much the "dry" surface will affect any readings. Well, I'm going to talk with someone about this later, someone who's expertise is food safety. She will know more than me for sure. :D

 

You mention a perhaps-crucial issue:  Is it just the surface of the ganache that is drying out, therefore leading to the possibility that the later reading is not a true reflection of the Aw?  Today, as it happens, I am making your cinnamon bonbon ganache, so this time I will take three samples, measuring one as I have done with the recent ones, keeping one covered between the two readings, and stirring up the third one before the second measurement.

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Here are the results from the latest tests:

 

Time Frame of Readings:

A = immediately after ganache was made

B = 3 hours later

C = 12 hours after reading B

 

Readings for Each Sample:

1 = sample was left uncovered for all readings and was not stirred until before reading C

A = 0.69

B = 0.58

C = 0.69

 

2 = sample was covered between all readings and was not stirred until before reading C

A = 0.69

B = 0.75

C = 0.75

 

3 = sample was left uncovered for all readings and stirred before readings A and C

A = 0.67

B = 0.70

C = 0.69

 

The instrument was the Pawkit from Meter Group (previously Decagon Devices). The readings are supposed to be accurate within 0.2 [correction: 0.02] units of water activity.

 

For me, Sample 1 is the most relevant because the readings clearly show that my previous conclusion, that by simply letting a ganache sit for a while its Aw will decrease, was inaccurate.  I should have thought of the fact that the meter was measuring the top surface (at least I think that's what it does).  The 0.69 reading stubbornly remains the same when the sample is stirred.

 

I am puzzled by the readings for sample 2 (which was covered throughout): they actually rise over time, whether stirred or not.

 

I would think sample 3 most clearly parallels what the chocolatier experiences since stirring the sample before readings brings more of the ganache to the top for measuring each time (why the second reading rose I cannot explain).

 

My (disappointing) conclusion:  The Aw reading of a ganache remains approximately the same throughout the process--what you initially make is what you get.  There are, it would seem, no magic factors in getting the water level activity lower.

Edited by Jim D.
Correct error in Pawkit readings (log)
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The readings are supposed to be accurate within 0.2 units of water activity.

 

I think it is .02.

Jim, I have found about the same as you have. They change slightly, but not much.

Ruth Kendrick

Chocolot
Artisan Chocolates and Toffees
www.chocolot.com

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31 minutes ago, Chocolot said:

The readings are supposed to be accurate within 0.2 units of water activity.

 

I think it is .02.

Jim, I have found about the same as you have. They change slightly, but not much.

Good to know that you have had more or less the same experience. And thanks for catching the error in the Pawkit readings.

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  • 1 month later...
On 8/4/2021 at 1:18 PM, Jim D. said:

Here are the results from the latest tests:

 

Time Frame of Readings:

A = immediately after ganache was made

B = 3 hours later

C = 12 hours after reading B

 

Readings for Each Sample:

1 = sample was left uncovered for all readings and was not stirred until before reading C

A = 0.69

B = 0.58

C = 0.69

 

2 = sample was covered between all readings and was not stirred until before reading C

A = 0.69

B = 0.75

C = 0.75

 

3 = sample was left uncovered for all readings and stirred before readings A and C

A = 0.67

B = 0.70

C = 0.69

 

The instrument was the Pawkit from Meter Group (previously Decagon Devices). The readings are supposed to be accurate within 0.2 [correction: 0.02] units of water activity.

 

For me, Sample 1 is the most relevant because the readings clearly show that my previous conclusion, that by simply letting a ganache sit for a while its Aw will decrease, was inaccurate.  I should have thought of the fact that the meter was measuring the top surface (at least I think that's what it does).  The 0.69 reading stubbornly remains the same when the sample is stirred.

 

I am puzzled by the readings for sample 2 (which was covered throughout): they actually rise over time, whether stirred or not.

 

I would think sample 3 most clearly parallels what the chocolatier experiences since stirring the sample before readings brings more of the ganache to the top for measuring each time (why the second reading rose I cannot explain).

 

My (disappointing) conclusion:  The Aw reading of a ganache remains approximately the same throughout the process--what you initially make is what you get.  There are, it would seem, no magic factors in getting the water level activity lower.

I was away for quite a while and I can't believe I've almost missed this. Thank you so much for sharing all your experiments! This issue had been puzzling me for so long. You are the real MVP

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On 8/2/2021 at 1:21 PM, Jim D. said:

I have performed the experiment once more and am getting what one might call a "consistent inconsistency."  I made Wybauw's pear recipe (Fine Chocolates Gold, p. 309).  The Aw reading immediately after the ganache was piped was 0.78.  Approximately three hours later, the same sample produced a reading of 0.64.  For someone who is quite cautious about shelf life issues, these readings are very good news.

Wybauw has that recipe listed at 0.84 Aw. Are you doing anything differently that you can tell?

 

Alternatively, have you ever cross referenced a result from your meter with a lab to check for calibration?

Edited by wannabechocolatier (log)
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6 hours ago, wannabechocolatier said:

Wybauw has that recipe listed at 0.84 Aw. Are you doing anything differently that you can tell?

 

Alternatively, have you ever cross referenced a result from your meter with a lab to check for calibration?

 

I have found that Aw readings differ from one batch to another, always within the same general range but different numbers.  Of course that is not difficult to understand since measuring is an inexact science (at least when done by me). I followed Wybauw's recipe without any changes.

 

No, I have never sent a sample for testing elsewhere.  I am content with a reading below 0.80 (with a couple of exceptions--both Wybauw recipes too delicious to give up in spite of readings above 0.80).  If the reading for a new recipe is too far above 0.80, I look for ways to change it to add some solids or eliminate some water or else I abandon it entirely.  I have had one mold episode and have never forgotten the sight!  Of all things it was in a pâte de fruit (one assumes all that sugar will protect it), so now I add a bit of sorbic acid to all PdFs.  As for the meter, it is the least expensive one that I know of (if $2200+ can ever be called inexpensive), and I don't expect it to provide extreme accuracy.  It is a model that many food inspectors commonly carry around with them and so has to endure some abuse.  It does come with test vials of salt water, and so far the reading has been exactly what the vial says it is supposed to be.  My kitchen inspector is impressed that I have the meter, and that counts for something, I suppose.

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3 hours ago, Jim D. said:

 

I have found that Aw readings differ from one batch to another, always within the same general range but different numbers.  Of course that is not difficult to understand since measuring is an inexact science (at least when done by me). I followed Wybauw's recipe without any changes.

 

No, I have never sent a sample for testing elsewhere.  I am content with a reading below 0.80 (with a couple of exceptions--both Wybauw recipes too delicious to give up in spite of readings above 0.80).  If the reading for a new recipe is too far above 0.80, I look for ways to change it to add some solids or eliminate some water or else I abandon it entirely.  I have had one mold episode and have never forgotten the sight!  Of all things it was in a pâte de fruit (one assumes all that sugar will protect it), so now I add a bit of sorbic acid to all PdFs.  As for the meter, it is the least expensive one that I know of (if $2200+ can ever be called inexpensive), and I don't expect it to provide extreme accuracy.  It is a model that many food inspectors commonly carry around with them and so has to endure some abuse.  It does come with test vials of salt water, and so far the reading has been exactly what the vial says it is supposed to be.  My kitchen inspector is impressed that I have the meter, and that counts for something, I suppose.

Wow, how long had the pâte de fruit been sitting?

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27 minutes ago, wannabechocolatier said:

Wow, how long had the pâte de fruit been sitting?

 

That's an interesting question.  As you can imagine, I obsessed over what had gone wrong.  The bonbon had layers of strawberry PdF and lemon ganache.  The pieces I left in a storage room (at 60F) were the ones that had the mold (not sure how long they were there).  Those I had frozen had no trace.  So there were not many that were affected, and no one at the retail outlet where they are sold reported a problem.  But I freaked out and contacted anyone who had some of them.  Nobody, for what it's worth, had noticed anything wrong.  One customer said simply, "Oh, we've already eaten those, no problem."  But it was a turning point for me, as you can well imagine.  I now refrigerate or freeze (in sealed bags to minimize condensation) everything as soon as possible.  And the retail outlet has been taught to keep some of the boxes I deliver in a freezer, others for immediate sale in a refrigerated case.  As far as I am concerned, freezing is the way to go.  I have never noticed any defect in a frozen and proper thawed bonbon--and no mold! 

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