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Aug 9 / scott.campbell

Beef Jerky and Water Activity

A special thanks to John for faithfully posting updates on his prosciutto during my extended period of burnout.  I realize I haven’t even posted the final results for the tuscan salami, but it didn’t turn out great, so it’s difficult to get excited about it.  The prosciutto experiment seems to be going well, and I’m looking forward to eating some nice cured ham … in 8 months when it’s done.

It’s only by chance that I got suckered into making another “test” product.  My sister’s pregnancy may sound like a strange reason to start a beef jerky project.  Overnight, she developed olfactory senses usually reserved for the world-class sommelier, and began hunting for foods that seemed even marginally appetizing.  In particular, she lamented the fact that nearly all beef jerky is really sweet these days.

This is where I come in.  Alton Brown has a great beef jerky recipe,  so I asked my wife to pick up some flank steak at Walmart.  A quick aside: where does Walmart get off charging $8/lb. for flank steak?  Just one more reason not to shop there.  Anyway, I sliced up the steak and got it marinating, a process that lasted for 6 hours.

Once done, it was time to dry the strips of meat out.  Alton suggests 3 air conditioning filters bungee-corded to a box fan for this process.  I own neither item, so I pressed a dehydrator my wife bought a while back into service.  The dehydrator doesn’t technically work like Alton’s set up, which only dries but does not heat the meat.  The dehydrator uses a heating element to make warm air, which then flows upward, creating a draft that dries out the meat.  I checked the temperature throughout the process, and found the meat got up to about 130F, kind of high, but not terrible.

The strips of flank steak basking on the dehydrator trays looked like this:

Yes – I neglected to eradicate strips of fat from the flank steak.  Anyway, halfway through the process, the beef jerky looked like this:

You can see that the edges are starting to dry out, but the center of the meat is still red.  Finally, when done, the strips had taken on a dark brown color, kind of like the stringy, leathery product you might get at a truck stop on the freeway:

Now, to the water activity.  I actually made 2 batches.  The first batch I just dried and measured after 12 hours of dehydrating.  Its water activity was 0.628 – a really good level, because it inhibits nearly all microbial growth, but is high enough that the meat hadn’t turned completely stiff.  To eat it, you definitely have to gnaw on it, but that’s part of the fun, in my opinion.

The 2nd batch, I took water activity and weight readings.  The data look like this:

Over the period of 12 hours, the jerky loses over 2/3 of its weight.  Also, the weight starts to drop almost right away.  The water activity is a different story:

Its over 8 hours into the drying cycle before the water activity starts to drop at all.  Once it does, however, it continues to decline rapidly right up to the point the jerky is “done”.  This suggests that people who make jerky should really monitor water activity closely, because small differences in drying time can affect their product a lot.  The jerky itself didn’t fail to impress – tough but a little chewy, spicy but not hot.

And what of my sister?  She took one bite of the jerky and declared: “it’s really good, but it doesn’t work”.  What does work? Oyster crackers and string cheese.  Not to worry – my kids absolutely love the jerky, and the remainder of it will go camping with me and my family next week.

Download The Food Manufacturer’s Complete Guide to Water Activity—>


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  1. James / Oct 14 2012

    How did you measure Water Activity?

    • scott.campbell / Oct 16 2012

      James – Thanks for your question. My interest in cured meats comes partly from my day job at a water activity meter company – Decagon Devices. So the meter we used was just the one my company makes – the AquaLab 4TE.

      • James / Oct 18 2012

        Thanks. I was hoping that you had an inexpensive test for home use. I have looked at the Aqualab products, but they are not for home/enthusiast use. I am trying to formulate jerky recipes for safe manufacture at home:

        In the end, for a home jerky maker, you are really left to guess water activity.

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