Yeast allergy is a really tricky one to manage. Yeast isn’t a food as such (nutritional yeast aside), it’s a living organism, and it’s everywhere. It’s in most of us, it’s on the skin of fruit, it’s in the air… That’s how sourdough bread works: you basically trap the yeast from the surroundings in your starter and then keep it alive. So saying a recipe is ‘yeast free’ is difficult to judge, and the amount of yeast a recipe might incorporate is dependent on how much yeast is present in the ingredients you are using that day. Today’s blueberries might be covered in the stuff, tomorrow’s might be less yeasty.
Some food stuffs are more obviously yeasty. Bread, for example, or beer, or yeast extract or nutritional yeast. They are obviously to be avoided. As mentioned above, fruit, and particularly dried fruit, is often covered in yeast. Anything which has been fermented will contain yeast, so that includes soy sauce, fish sauce, fermented vegetables, vinegar (although distilled vinegar is usually OK), and alcohol (again, distilled spirits such as vodka are usually tolerated in small amounts). Sprouted beans, seeds and grains may also antagonise a yeast allergy as they need to sit in a warm damp environment for a few days: this is also the perfect enviroment for yeast growth. Finally sweeteners, sauces and condiments that sit in a jar in the cupboard for a while may pick up yeast. Squeezy bottles may be better because the food doesn’t come into contact with spoons etc when you use it. Better still may be dried ingredients such as coconut sugar rather than syrups; dry mustard powder rather than wet mustard in a jar. When buying wet condiments it may be best to choose smaller jars so they are used up more quickly.
The amount of yeast a sufferer tolerates will differ from person to person, and how you manage your yeast allergy is a personal thing. If you are sensitive to yeast you know what will antagonise your symptoms much better than I do! I have tried to label recipes as ‘yeast free’ if they are unlikely to contain a lot of yeast, but please use your own judgement.