Water Activity meters, testing, and benchmark recipes

We are starting a small molded and slabbed chocolates business from our home kitchen.  Our state requires water activity levels below 0.85, as tested at a certified lab.  Those tests run $75 each, and travel cost pushes it up substantially.  We can't avoid the tests, and we don't want to, but we do want to avoid wasting ingredients and time on recipes that won't pass.

I've read everything I could find on the internet about this subject.  From forums here and elsewhere, to obscure papers found on page nine of a google search.  I know Wybauw covers the subject in detail in book 3, but from what I've read, he relies heavily on sorbitol, something we don't want to include in our products.  

New meters start a bit over $2000, and for $3000 you get a lot better accuracy.  We may well buy one, but it is a considerable expense.  I've seen software that estimates water activity from recipes, but that isn't cheap either, and I have no idea if their databases are geared towards confections.  

I am really surprised that nobody has compiled a list of water activity readings for classic recipes, say a Greweling piped ganache, or a Shotts caramel.  I know technique will lead to varying results (cream heated longer, etc).  Still, it would be handy to have a set of baseline recipes and aW numbers.

I suspect we'll end up purchasing one of these units.  When we do, we'll share results.  Meanwhile, if anybody has any advice for us, we are all ears!

Thanks

M

Rotronic makes sensors that they claim offer .008% accuracy on aW for about $1500 that you can plug into a PC running their software.

There is software written that estimates aW and shelf life (and other things, including recipe cost) from confectionery recipes. I don't know the price.

There are many recipes on the internet for making your own invert sugar. The only extra ingredient you need - other than sugar and water - is either tartaric acid (cream of tartar) or citric acid. This makes for a clean ingredient label if you want to go that way. Honey is an invert sugar, too.

When it comes to aW numbers in a classic recipes database - it's an interesting idea and when you get your water meter I hope you'll share some of your insights! It's not as straightforward as it seems, just thinking about it for a few minutes.

I purchased a Decagon PawKit used for $500. It has been invaluable as I develop my formulas. If you have a State University nearby, they can test your ganaches for you. 

Thanks Ruth and Clay!  The software looks interesting.  My fiancee used similar software at a wholesale gelato place she worked, and it was very helpful in recipe development.  Probably more than we need right now, but worth knowing about.  We've been looking at invert sugar (she is very familiar with it from her work) and I found some Wybauw recipes online that use it without sorbitol.  Those have aW values, and give us a starting point.  

We'd snap up a Pawkit at $500 in a second.  You got quite the deal Ruth!  Other than one seller in Indonesia we've not seen anything in that range.  A bit over $2k new and the few sales on the auction site have sold closer to $1000.  The .02 accuracy is also a bit of an issue.  I found the mold free shelf life estimator calculation online and a few percent in water activity can nearly double shelf life.  Even if there is variation batch to batch in that range, it adds to the uncertainty.

I spoke with someone at Rotronic before posting this thread and was under the impression that the .008% meter is around $1500 for the sensor chamber (required) and then you need either the hand held reader (also around that price) or the software as you mention Clay.  I didn't think to ask for the software price, but reading about it made it sound quite sophisticated (that's fine) but presumeably expensive.  Sensible for a large operation but not for the two of us just starting out.  If that meter is $1500 outright, plus the few additional expenses for cups and what have you, it seems like a great deal.  At $3000 it seems very fair, but not an easy purchase for us.

Our understanding is that U Mass doesn't do the cheap testing, so we need a commercial lab.  We'll need that anyhow with final recipes for the health dept.  Perhaps we will just start with one of the Wybauw ganache recipes we found and also one of my fiancee's favorites, pay for the tests, and develop from there.

The biggest discovery in this process so far is the very short estimated shelf life of ganache right at that .85 threshold.  Eleven days at 72 degrees. Not that we'd store that high.  And I know sanitation, technique, packagaing and storage play huge roles in shelf life.  When your business model is primarily wholesale, even if only local, a few points in aW really matter.  The "three weeks" you usually hear for cream based ganaches seems optimistic, unless the enrobing greatly slows mold growth.

Anyhow, thanks for all the help.

M

Care to share the link so that others can work with it as well?

Sorry Clay, of course.  I am involved in a fishing forum that prohibits linking to outside sites, and I guess it has become habit to avoid it.  I'm also glad you asked because I made a mistake in the holding temperature I mentioned.  It is around 70f not 72f.

I found it on Wikipedia.  I then managed to track it elsewhere but can't remember the link.  I think it was from a google books preview.  

Wikipedia Water Activity

You will find the formula in section 1 right after the introduction.  Abbreviated as MFSL = 

I will also share that I found the Wybauw recipes here:

Wybauw Fine Chocolates Preview

Although many pages are left out, there were enough samples to be helpful.  

There is no preview for his second book in the series that focuses on Ganache.  We'd buy it if it were similar to this.  We haven't bought book 3 on shelf life because it is so sorbitol dependent.  We received book 4 as a gift, and while it is interesting, it is also heavily reliant on ingredients we don't think we want on our labels.

If anybody has a copy of Wybauw 2 Ganache and wants to share how helpful the recipes are likely to be for us (water activity given, limited use of sugar alcohols) we'd love to hear your feedback.  We'd purchase it if it fit.

Thanks,

M

 Weird, I just checked my link to the book preview and the recipe pages weren't available.  When I found the preview, I'd done a specific google search on this subject, including his name and possibly invert sugar.  I don't remember.  It gave me a different preview.  Blocked in different places.  I got perhaps a dozen recipes from it.  I don't know how Google preview works, but that link I gave is unlikely to be of use to others for finding recipes with aW.  If you try my approach I just mentioned here, it might work.  

Please note, I am in no way trying to help people get copyrighted material they shouldn't have.  Previews are given to entice people to buy the book.  I certainly hope Mr. Wybauw sells more books through this strategy.  He'll probably end up selling book 2 to me because of it.

I got the Pawkit on Craigs list. Kerry Beal found it for me. Decagon also sells refurbished units. You want a State university for cheap testing. The .02 isn't much of an issue. I want my ganaches well below the .85. I like them in the low 70's. I get 2-3 months, no mold, but flavor fades.

Prochoc is available for about 110 Euro from Libaire Gourmand - it's in french.  

Hey Ruth, just wanted to let you know that I spoke with Decagon on the phone this morning after chatting with Kerry on egullet about them selling refurbished/used units and doesn't sound like they do that anymore unfortunately, so I'm guessing the best way to find one used is to continue to search for them on Craigslist/ebay.  The quote I got from Decagon for the paWkit was $1998 for the unit, then $388 in accessories.  They do offer a payment plan though, where you put 20% down, then pay the balance over the next 9 months interest free.  Something to think about @elephant if it's something you're serious about.  I'm definitely going to keep looking for a used unit, but if I can't find one by the time I set up shop then I might consider taking advantage of the payment plan option.