Many recipes for apple pie and apple cobbler will call for tossing your sliced apples in a little bit of lemon juice before putting them into your dish. Lemon juice prevents oxidation of the apples, which means that it stops the slices from turning brown by providing a barrier between the apple’s flesh and the air. Lemon juice definitely works when it comes to preventing the browning of fruit, but a better question is do you really need to use it when baking an apple pie?
This is a good question because I know more than one person who has rushed around looking for a lemon, fearful of browning the apples that will go into their pie because it might make them “look funny.” The short answer is no, you do not need to add any lemon juice to an apple pie or many other baked apple desserts.
In the case of that pie, you are going to toss your apples in brown sugar, cinnamon and other spices and put them in the oven to cook for at least an hour or so. Not only are many of the pie’s filling components brown to begin with, but you want your apples to turn tender and golden as they bake – not to remain pale and appear to be uncooked. Of course, the apples will cook regardless of whether lemon juice has been added, but giving them a very slight head start on browning by exposing them to air for a few minutes can actually make for a more attractive pie filling. This is a tip that has been given to me many times by chefs (mostly by chefs who also teach) and it is definitely true when you compare a browner, richer-looking pie filling to a very pale one. There is no need to add lemon juice to prevent discoloration when baking with apples. It won’t hurt the filling to have the lemon juice in there, but tossing the apples in juice isn’t necessarily benefiting the dessert, either.
Preventing discoloration is probably the most common reason to toss apples in lemon juice, but one other reason that lemon juice is added to a pie filling is to add some extra tartness to a batch of not-too-tart apples for those who don’t like their pie to be too sweet. I’ve found that adding a tablespoon or two of lemon juice does not do much to increase the tartness of apples when you have 2-3 lbs of apples going into a pie. Again, it can’t hurt the filling, but a better solution is to really try to find apples that suit your tastes (such as tart Granny Smiths) for better results.