How to Query Database for posts with certain Taxonomy Term

(I realize you’re leaning away from this, but maybe if you can get it working, it’s worthwhile. With the recent perfomance improvements in 3.4 for WP_Query, this could be worthwhile.)

WP_Query is the right decision if this is a secondary loop. Otherwise, you might look into pre_get_posts.

When you use WP_Query make sure that:

1. You don’t use a reserved global variable to save your new query. (For instance, a lot of people cause problems by saving their new query as $wp_query and then they overwrite their existing query object.
2. You use the right loop format e.g. $my_custom_query->have_posts();
3. Finally, rather than using tag or the tax var (which is deprecated), use a tax_query.

Looking at your example, here’s a suggested loop:

$food_query_args = array(
    'post_type' => 'projects',
    'tax_query' => array(
        array(
            'taxonomy' => 'post_tag', // or the name of your custom taxonomy
            'field' => 'slug',
            'terms' => 'food-and-beverage' // FYI, it's more stable imho to use the ID if you can. If you do, that switch 'slug' in the preceding line to 'id'
        )
    )
);

$food_query = new WP_Query( $food_query_args );

if( $food_query->have_posts() ) : while( $food_query->have_posts() ) : $food_query->the_post();

    // STUFF

endwhile; endif; wp_reset_postdata();