Texture and Water Activity

Snap, Crackle, Flop

A consumer bites into a candy bar, and it goes "crunch".  This may or may not be good news.  If it was supposed to go "crunch" and it's part of that treat's identity, no problem.  If the snack is supposed to be soft and chewy, then it's a problem. 

Water and Texture

Water in a food product is a primary determinant of whether the product's texture performs well.   This is because water acts as a plasticizer in foods.  Nobody wants to eat a mouth full of protein powder, but mix in some water, and coat that square in chocolate, and you have a successful energy bar. 

There are two ways texture can go wrong: it can be wrong as soon as your product is made, or it can go wrong over time as your product sits on the shelf. 

Texture Problems

If a chewy chocolate chip cookie rolls off the production line already crispy, it's probably because too much water has been taken out in the baking process.  This is pretty straight forward - all you need to do is decrease the bake time or temperature to solve the problem.  Another complication occurs if products undergo phase change during storage.  These changes, including glass transition and crystallization, can make change smooth products to grainy ones, or soft products into hard bricks. 

Preventing Texture Problems

Water activity plays a key role in preventing such issues.  First, organoleptic factors can be used to define water activity levels that are acceptable during a manufacturing process.  Once you have set your specs, monitoring them is easy: just use a water activity meter on each lot or batch.  Using a Moisture Sorption Analyzer to identify problems before they start is even more powerful.  A moisture sorption isotherm can tell you what water activity levels are critical for texture changes.

Learn more about how isotherms can be used for texture research >>