Here is the answer from Arm & Hammer re: baking soda:

Thank you for visiting our web site. We appreciate your interest in our company and our products. It is nice to know that you enjoy using ARM & HAMMER® Baking Soda.

In response to your inquiry, no, it is not necessary to stir ARM & HAMMER® Baking Soda before use.

Again, thank you for taking the time and having the interest to contact us. It's always nice to hear from satisfied customers.

We hope you will visit our web site again at: WWW.CHURCHDWIGHT.COM; for information about our company, products, history, and financial information.

Based on the response from Arm & Hammer, it is not necessary to stir ARM & HAMMER® Baking Soda before use.

Based on the response from Arm & Hammer, the answer to the question is that it is not necessary to stir ARM & HAMMER® Baking Soda before use.