Learn the science behind:
Cooling cookies according to instructions is not my ‘forte’. I tend to pull the cookies out of the oven, place them on any spot I can find and continue doing what I was doing. Even if instructions say otherwise, I tend to do it the easy way. And since I don’t like following instructions if I don’t see what their use is, I decided to investigate ‘the best way to cool cookies (and why)’. Is there enough reason for me to change my ways of working?
It’s starts with baking cookies
You can’t cool cookies if you don’t bake them. During baking you transform the soft cookie dough into crunchy, chewy cookies. We’ve discussed what happens in the process in another post on baking cookies. During baking a lot of processes occur, some of which are irreversible, for example the denaturation of proteins or the browning of the cookie.
However, some of them can be reversed. Indeed, the science of food doesn’t stop after it’s been made. For the rest of its storage science will continue to work. For a bread we’ve discovered that the moment it comes out of the oven, the staling process starts. For a lot of products we’ve discussed how packaging extends shelf life. In the case of cooling cookies the most important aspect we have to take into account is moisture.
Moisture science & water activity
Water and movement of water is one of the most commonly returning topics in food. Water is important for shelf life, growth of micro organisms, sensory characteristics, etc. Both a too high or a too low moisture content can be undesirable. So controlling the amount of water and location of the water in foods tends to be very important.
However, water likes to travel and can do so quite easily. This is due to some basic physics which starts with a term that is used to describe the presence of water: water activity. The water activity of a product defines how much ‘available’ water there is. When the value is 1,0 there is 100% available water, when there is no water at all (which is extremely rare, especially in food) the water activity value is 0,0. Most fresh foods are somewhere between 0,9 and 1,0, thus they contain quite a bit of moisture.
Physical laws describe that the water activity of two components close to each other will always even out, as long as the moisture has the ability to move. In other words, if a cookie has very little water inside, but the air has quite a bit, the water will move from the air into the cookie. We have discussed this concept in greater detail when discussing strawberry pies. If a pie has a low moisture crunchy crust but a high moisture filling the crust tends to become soggy (moist) whereas the filling may become a little dry.
When cookies come out of the oven
What happens when cookies come out of the oven? First of all, a lot of the processes happening in the oven will continue happening: the starch & proteins will continue cooking and water will be evaporating. In the meantime the cookie will be cooling down. The thinner the cookie, that faster cooling goes and once the cookie has cooled down enough a lot of these processes won’t be occurring any more. But it’s not only the cookie shape that influences the cooling rate, how the cookie is cooled also helps:
- Rack: If the cookie is placed on a rack air can travel around the cookie, taking away the heat. This is generally the fastest way. Also, the air can take away any moisture that’s still evaporating from the cookie.
- Tray: A metal tray (probably the same one the cookies were baked on) still cools quite quickly. Metal transfers heat quickly, but moisture won’t evaporate at the bottom.
- Wood: Placing the cookies on a wooden tray doesn’t speed things up, the wooden tray will become more likely and wood can often take up moisture (which you don’t want to happen since it might make the bottom of the cookie soggy).
- Glass: glass doesn’t transfer heat so quickly, so tends to slow down cooling a bit.
So now we know what happens, but what do we actually want to happen?
Crunchy cookies requires moisture to escape
If we want crunchy crispy cookies it is essential that as much moisture as possible can escape from the cookie. It’s the low moisture content that makes a cookie crispy. So, during cooling we want as much moisture to leave as possible. What’s more, we want to prevent moisture from being able to come back in too quickly.
In other words, it’s best to cool the cookie on a rack and definitely not in glass or on wood. The wood will get moist and that will result in a moist cookie. Glass also tends to ‘catch’ moisture and hold on to it
Definitely do not pack the cookie before it has cooled down completely. As long as the cookie is warm moisture might evaporate. If the cookie is packed when it’s still warm this moisture will evaporate into the package. This will make the environment in the pack quite humid and that will result in some of that moisture moving back into the cookie, making it soggy instead of crispy.
Cooling chewy cookies
For chewy cookies the cooling process is a little less critical. Since we’re looking for a chewy cookie, we aren’t that bothered by a little more moisture in the cookie. Nevertheless, always prevent packaging too warm cookies since high moisture in a pack is almost never good for your cookie.
Anything else besides moisture?
Even though moisture is probably the most important factor to take into account, there are a few other things to take into account when cooling your cookies:
- Cookies are soft when they come out of the oven: don’t judge a cookie’s structure by the structure it has when it comes out of the oven. Since the fats are still melted, the starches still warm and the sugars still dissolved, they are still very soft. Only when they cool will they get to their final structure.
- Sugar dissolves better in water at higher temperatures. This means that at higher temperature (= in the oven) a lot of the sugar dissolves in water. However, at lower temperatures the sugar doesn’t dissolve in the water that well anymore and part of the sugar will recrystallize. This contributes greatly to the crispness of cooled down cookies.
Ok, so there’s a proper way to cool cookies. Nevertheless, despite the theories, for a home baker you can bake perfectly fine cookies if you don’t use a special cooling method. Things really start to change though when you scale up. Where will you leave all that heat? How do you prevent the cookies from influencing one another? That’s where the science described above becomes even more important. And as always, experiment in your kitchen and climate and see what works best for you!