One of the things I like best about enjoying food science, is the fact that once you’re into it, you see food science all around. I can’t bake a bread without thinking about the Maillard reaction or the fermentation process. Nor can I cut an apple and sprinkle lemon juice on without thinking about enzymatic browning. It’s fun, but also tends to make recipes fail. If I don’t see a good reason for doing what the recipe does, I might skip it or do it differently.
One of the things I tend to do different is how I use vanilla in my recipes. Sometimes I use a vanilla bean, other times I might use an extract. I use whichever I think is appropriate, or whichever one I have available. But I always used to buy vanilla extract. Until, I visited a family member who had home made vanilla extract! And I thought that was just downright brilliant. First of all, it’s cool to make, second, it’s a great example of applying science and third, because it’s probably a great new alternative to tweaking and modifying my recipes.
So today, we’ll dive into extraction chemistry (and making vanilla extract).
Extraction used in chemistry
Making vanilla extract uses a very common chemical process, that, if you’ve had some chemistry at school, you will have probably heard of: extraction. Extraction is used a lot in the field of organic chemistry. With extraction chemists can split and purify different components from a solution.
Chemists often end up with a mixture of molecules in their reaction beakers whereas they are only interested in one. The trick is to remove all the undesired components. Their are various separation techniques to do this, chemists can use heat, membranes and filters for instance. But another way is to use a difference in solubility of the components: in comes extraction.
Sounds a little complicated? Let’s take an example. Let’s assume we have a beaker filler with water and 2 other components: called A and B. We want to split A and B by using extraction.
Component B happens to dissolve well in water, but very poorly in oil. Component A on the other hand strongly prefers to sit in the oil instead of the water.
So, we add some oil to our mixture and shake it up. If we than leave it to sit, oil and water will separate out again, the oil will lie on top of the water. Component B will sit in the watery layer, but component A will sit in the oil! By pouring of the oil layer we will have an oil with quite a lot of component B and water with a lot of component A!
Extraction of vanilla
This same principle is then used to extract molecules from a solid component, such as, in our case, a vanilla bean!
A vanilla bean contains a lot of different molecules that contribute to the vanilla flavour as we discussed when comparing vanilla & vanillin. Vanilla contains a lot of different molecules, each contributing to its flavour.
These molecules all have a different structure. It would be too much to mention all the individual molecules here, but it is worthwhile mentioning the different structures. Don’t worry if you have no clue what they mean, for food chemists this is interesting, but otherwise, your take away message is: there are a lot of different types of molecules: tannins, polyphenols, free amino, acids, resins, acids, ethers, alcohols, acetals, heterocyclics, phenolics, hydrocarbons, esters and carbonyls (source). It is this wide variety of flavours that make vanilla taste very different then just plain vanillin.
Why use ethanol for extraction?
Some of these molecules dissolve well in water, but a lot of these don’t dissolve that well in water. But, they do dissolve pretty well in ethanol. By placing the vanilla pod in an alcohol/water mixture most of the components will eventually leave the pod itself and sit inside the liquid.
This is what makes the mixture so strong. If you would only use water for the extraction, a lot of the characteristic flavours simply wouldn’t leave the pod and it wouldn’t be as strong by far!
There are a lot of other so-called organic solvents that can be used to extract these type of molecules. Why not use one of these? Well, main reason most likely is that we wouldn’t like to have these in our food. Several of them are pretty poisonous! Ethanol is one of the few safe solvents that can be used here.
Another reason for people selling vanilla extract in alcohol in the USA is that the FDA requires vanilla extract to contain at least 35% alcohol. Not exactly sure why that is, but I assume it’s to guarantee an extract of sufficient strength and to prevent fake extracts.
Solubility of vanillin in ethanol vs water
A short intermezzo here. One of the main flavour molecules within vanilla is vanillin (see vanilla vs vanillin). Vanillin is one of the main molecules you’d want to extract when making a vanilla extract. The solubility of vanillin is 50mg/ml whereas it is only 10mg/ml in water (source). That illustrates once more why using ethanol instead of water gives such a stronger vanilla extract.
Why extract vanilla pods?
Good question, why not use chopped up vanilla pods or just fresh vanilla pods every time?
The first is a matter of cost effectiveness. Vanilla pods themselves are expensive. When using fresh vanilla beans, chances are as well that you won’t use most of the flavouring power. The pod itself for instance is generally not used, only the black powder inside. But, this pod contains a lot of flavour molecules. By making an extract you use up all of the vanilla pod.
Another reason might be flavour, when using a vanilla pod you often use some sort of heat to extract maximum flavour. If a recipe doesn’t require any heating chances are you won’t be able to take away that much flavour. So, adding vanilla extract will give a stronger flavour.
Vanilla pods can also be chopped into powder, as I’ve seen on various blogs. But, vanilla pods aren’t 100% dry so it is often hard to get a real dry powder. Furthermore, the pods themselves contain a lot of cellulose. This is a molecule in plants that gives them structure, but doesn’t contribute to flavour. By using a powder this is also incorporated. Whether or not this is a problem depends on the dish and your wishes on appearance and taste!
A vanilla extract recipe
Of course, now that you know what happens, you probably want to give extraction a try as well. So let’s make some vanilla extract!
- 3 vanilla pods
- Rum or vodka
- Take a nice looking small but high bottle (to make sure you don't need too much alcohol to submerge the vanilla pods).
- Cut the vanilla pods open and in half and place them in the bottle. It is not 100% necessary to slice them open, but I believe it will make extraction go faster since the powder gets to leave the vanilla pod more easily.
- Pour enough wodka or rum in the bottle to submerge the vanilla pods. Honestly, I haven't measured quantities. The best ratio will depend on your alcohol as well as vanilla bean quality.
- The extract should be done after approximately one month. Don't be afraid to store it any longer, it will only become more intenste over time. The high alcohol percentage will prevent spoilage.
For the hard core chemists, there are a few interesting scientific articles out there for diving into vanilla extraction in more detail!