M&S Thick Sliced Tiger Bloomer Made with our 30-year-old sourdough starter culture and topped with a classic tiger crust, this loaf is perfect for making sandwiches or dunking into warming soups. All of our breads are a natural source of Vitamin D and Fibre, two nutrients that are naturally low in our diets. We use a natural source of Vitamin D that is produced by yeast, which is why you will find ‘yeast’ on our list of ingredients, not because we use it as part of the dough making process.