Learn the science behind:
You can make a cake with very few ingredients, equal amounts of flour, butter, eggs and sugar will give you a delicious pound cake. However, you can tweak the flavour and texture of your cake in an unlimited number of ways. For instance, we’ve discussed why you would use zucchini or carrots (even purple ones!) in a cake and how you can replace the eggs with corn starch. Of course there’s plenty more interesting variations to make.
Using sour cream is just one of those variations, which we tested out when making a recipe from Sweet, one of Ottolenghi’s cookbooks. Specifically, it asked to mix the baking soda with the sour cream (and yogurt) on forehand. As always with recipes from Sweet, it turned out great. But it did get us wondering, why even use the sour cream in your cake? What does it do, and how best to use it?
What is sour cream?
Sour cream truly is what the name says it is: a sour cream. In other words: cream that has turned sour (on purpose). In most cases micro organisms as used to make the cream turn sour. In doing so, it also thickens the cream somewhat and creates a lot of other flavours within the cream.
Since people did not have access to refrigeration like we do nowadays, the milk would be stored at room temperature. Milk is full of nutrients for micro organisms and as such microorganisms such as bacteria, yeasts and moulds could grow in the milk. These micro organisms produce all sorts of flavours and can make the liquid sour. Sour cream, but also creme fraiche for instance, originate from this natural process. Nowadays the process is a lot more tightly controlled, but still based on those same principles.
Sour cream characteristics
The growth of bacteria is what gives sour cream its specific properties. The bacteria produce all sorts of flavour molecules, such as diacetyl and also thicken the cream. This thickening occurs mostly because of the acidity which affects the behaviour proteins (caseins) in the cream. It is somewhat similar to what happens when making paneer cheese.
Why to use sour cream in your cakes
There are actually a lot of reasons why sour cream may be used in cakes! We’ll tick of the most important reasons. Understanding all these nuances and differences between ingredients is what will make you a better cook/chef in the long term and help you to develop new delicious recipes!
The first, most commonly mentioned reasons for using sour cream is its thickness.
If you’re baking a cake you are looking for a certain consistency of your batter. You want a batter that is not too runny or it will not be strong enough to hold onto any air that is formed and expanded during baking. At the same time, you want it to be runny enough to properly expand during baking.
Since sour cream itself has a consistency which is not too far off from that of a cake batter, it can be added quite easily without really affecting the consistency of the batter that much. This can be very beneficial if you’d like to add some more moisture to your batter, but already have quite a liquid batter. Adding something such as orange juice would thin your batter too much, whereas sour cream won’t have that much impact.
Browning of your cake & sour cream
When making a cake your recipe has to be sufficiently balanced so that it bakes on the inside, without burning on the outside. Of course temperature plays a big role here, but so does the composition of your cake batter. The main players in browning of your cake are proteins and sugars. More proteins and sugars will speed up the reaction.
Let’s compare butter and sour cream here. Butter contains very little lactose (a sugar) whereas sour cream tends to contain 3-4w% of lactose. This will make a recipe with sour cream instead of butter brown a little faster in the oven! That said, the low acidity of sour cream will slow down the browning reaction again! What the final effect will be will depend on whether there are other sour ingredients as well (in which case the extra acidity of sour cream might be less important) or how much sugar is there in total.
Activating your baking soda
Most cake recipes use some sort of a leavening agent such as baking soda or baking powder. These help to create a light and airy cake by releasing gases during baking. These gases help your cake to expand.
Baking soda and baking powder are very similar (which we discuss in more detail here). In fact, one of the ingredients of baking powder is baking soda, so both have baking soda as their active ingredient. Baking soda only works as a leavening agent if enough acid is present. In baking powder this acid has already been added, but baking soda requires you to add something acidic. Sour cream can be this sour component!
Generally, you wouldn’t use sour cream, just to activate the baking soda though. In that case you could also just use baking powder. However, you do tend to use at least some baking soda if you have sour cream since it neutralizes some of the acidity. A sour cream cake definitely does not have to taste sour.
Sour cream is made from cream and such contains a decent amount of fat. You add fat to your cake to make your cake richer. Cakes without any fat tend to be light and delicate, but drier (e.g. Angel food cake). Cakes with fat are less delicate but are richer and creamier (e.g. pound cake).
Alternatives for sour cream
To summarize, sour cream can be used in cakes to: add moisture without thinning the cake batter, adding fat for creaminess, controlling browning and to activate baking soda. The sour cream does all of this thanks to its high fat content & acidity. If you want to replace sour cream, you’d want to know why you’re using sour cream (is it because of the acidity or creaminess for instance). Then you’re able to decide which one to use.
Buttermilk and lemon juice for instance would be a good replacements to get that acidity, but they lack the fat. The most universal replacement would be a (thick) yogurt.
Sour cream vs (Greek) yogurt
If you’re using sour cream to add some extra moisture, while keep the consistency the same a good alternative would be yogurt. It’s also somewhat thicker, but contains a lot of moisture as well. However, there’s an interesting difference here. Apparently, sour cream contains less casein proteins than yogurt. Casein can improve the fluffiness of a cake, so using sour cream will make a less fluffy cake than using Greek yogurt.
Using sour cream
Overall, you will find that sour cream is often used to improve the texture of a cake and maybe to cut through some of the sweetness, thanks to its acidity. A lot of recipes will ask you to pre-blend the sour cream and baking soda at the start. The reason for this remains vague. If you want the sour cream and baking soda to neutralize in pH at the start, this will definitely do so. However, in the process of doing so, the baking soda will loose most of its leavening power (which is why you will often see baking soda being used in these recipes as well). In some cases this might actually be desirable though.
Harold McGee, On Food and Cooking
Khymos blog, Maximizing food flavour by optimizing the Maillard reaction, link
Serious Eats, How to make sour cream pound cake moist and tender every time, 9 June 2017, link
USDA national nutrient database, link
P. Walstra et. al., Dairy science and technology 2nd edition, 2005, link, p. 368 (Table 13.4) & 552