After sugar and salt it was a bit of a struggle to decide what to learn about next. Before I knew it I was tangled in a whole range of dairy products with all their unique effects. In the end I slapped myself to focus on milk. It's quite hard to explain the effects of milk without also explaining the use of other dairy products, but I will do my best to stay focused!
One thing about milk you might already know: it makes cakes and breads fluffy. I always use a few spoons milk in cake batters or add a few spoons milk powder to breads for that very reason. It's my little miracle ingredient. But milk doesn't only make cakes soft. Milk affects the taste, colour and texture of baked goods, but doesn't stop at that!
Not surprisingly, milk has an effect on the taste of baked goods. Especially when using flavoured milks or buttermilk you will notice this difference. Milk also encourages the browning of cakes and breads. It produces that creamy coloured crumb and the lovely golden crust. As a glaze milk gives buns a soft and golden shine. As you know sugar affects the browning process by caramelizing and thus giving baked goods a brown colour. The natural sugars in milk, lactose, do exactly the same. However, milk as opposed to sugar rarely results in a burnt crust.
Besides lactose milk also contains proteins. Proteins and lactose affect the texture of baked goods. Proteins in milk help form the structure of a cake. They reinforce the formation of gluten and stabilize emulsions. At the same time the lactose, like sugar, inhibits this effect. Lactose binds itself to the flour proteins and thereby hinders the gluten formation. In other words milk is considered a 'strengthener' of baked goods, giving it structure and enhancing the crumb. Yet at the same time it keeps the texture of the crumb moist and fluffy and the crust tender. For this reason you will notice that milk is used in cakes and sweet bakes, while we use water in breads or savory loaf.
We're not finshed
Milk doesn't stop at that. It hydrates and emulsifies the ingredients by dissolving the the individual ingredients into the batter. Milk provides food for the leavening agents. It gives cakes and breads a longer shelf life and the fat in milk prevents burning. Finally, milk contributes in nutrients as proteins and lactose aren't the only components of milk. Milk also
contains vitamins, minerals and fats that are essential to our diets. About 87% of milk is water: another essential ingredients for our bodies.
What milk to use?
There are a lot of different types of milk, ranging from fat-percentage to taste to the process with which it was made. Different types of milk include non-fat milk, skimmed milk, semi-skimmed milk, full/whole milk, raw milk, milk with additives such as nutrients or flavours, Long-life/UHT milk, buttermilk, drink-yogurt and kefir. Most of these are also available from animals other than cows such as goats, sheep or horses. Milk can also come from nuts or plants: think of soy milk, coconut milk, almond milk or rice milk. All these milks can be used interchangably, but will have slightly different effect on the end results. For instance, milks with more fat will burns less easily and buttermilk will give an even more moist texture to baked goods while almond or rice milk will result in a less fluffy and golden loaf. For most baked goods you will want to go for a fresh whole milk. Fresh milk can be replaced with milk powder, which will turn out to be an even better option when you have a long rising time for breads or if you need your batter to set as powdered milk doesn't deteriorate.
That leaves us the question: can we go wrong with too much or too little milk? However the answer to this question has little to do with the actual properties of milk, rather than the consistency of the dough. Too little liquids will result in hard rocks of flour and too much liquids will result in a goo that will never turn solid in any oven. Still, adding a bit of milk to cake batter or bread doughs can go a long way in making your end product softer and fluffier. Don't forget it also enhances the taste, colour, shelf-life and nutritional value!
Bread by Christine Ingram and Jennie Shapter
Vol of halfvol? by Wilma van Hoeven
Livestrong - What does milk do in baking?
baking911 - How baking works
Culinate - Kitchen Chemistry
The Dairy Council - Varieties of Milk