I am reading Under Pressure: Cooking Sous Vide by Thomas Keller (2008, Artisan), and noticed this (page 78):
Herbs, spices, and garlic should not come in direct contact with food that is vacuum-packed and cooked sous vide, as the flavor will be stronger in areas where there is direct contact. To avoid this, we make sachets, which allows the flavors to infuse the other ingredients evenly.
Place a piece of food-safe plastic wrap large enough to roll up the herbs, spices, and garlic on the work surface. Lay the herbs on the wrap and nestle any garlic and spices in the herbs. Roll up the sachet, and cut off the ends of the roll. Add the sachet to the sous vide bag with the other ingredients; discard after cooking.
Keller’s dictum resonated well with Dr. Douglas Baldwin’s caution from his Sous Vide for the Home Cook
Seasoning can be a little tricky when cooking sous vide: while many herbs and spices act as expected, others are amplified and can easily overpower a dish.