The Secret Science of Vanilla: Connecting Whisky and Vanilla Flavoured Foods
Bowmore Distillery
Islay, Scotland
In the interest of flavour and the inter-connectivity of things, let’s talk about something familiar to most all of us - vanilla! Well, more specifically, whisky production and flavour, and how this relates to the vanilla flavour in some of our go-to treats!
The linking element between that 16 year old spirit in your Glencairn and that creamy ice cream in your cone rests in a few key volatile chemical compounds. How do they arrive in such mutually exclusive products, tickling the senses of the young and old, alike?
On Vanilla
You can find it all around you, in ice cream, pie, cookies, even in beer: vanilla. It's one of the most popular flavours of foods and snacks. Seeing its enormous prevalence, you probably wouldn't expect that making natural vanilla is a complex process. It's one of the reasons why most products will actually contain artificial instead of natural vanilla.
Nevertheless, natural vanilla is still used widely, and also researched a lot. As a matter of fact, scientists still don't really know how that complex aroma and flavour is formed. Natural vanilla contains over 200 aroma compounds and it is pretty amazing that nature is able to make this. Certainly worth a deep dive into the manufacturing and science of vanilla.
Where vanilla comes from
The vanilla we use in our pies, ice cream, and other sweets starts as vanilla pods on a vanilla plant, which is actually an orchid. It is native to Mexico, but nowadays it is mostly grown in Madagascar, Indonesia and various south pacific islands.
Fresh vanilla pods are green and look a bit like regular green beans you'd have for dinner. They will only start growing after the plant’s flower has been pollinated. A task now often done by hand! These green pods take about 6-9 months to grow and develop but don't yet have any of that vanilla flavour that the final brown pods in your supermarket have. That said, they have accumulated a range of chemical components that serve as pre-cursors for vanilla. It's up to the farmers to transform the flavourless green pod into a fragant brown stick.
Curing vanilla pods
This transformation takes place during the curing of the pods which is generally done on or close to the farm where the pods are grown. The process starts within a few days after harvest. Each region or even farm tends to have their own best practices, developed over the years. Because of this, processing of the vanilla can be different everywhere. Some processes involve more or less steps, whereas others consist of similar steps, but are executed differently.
We'll walk through a common curing process of the pods. As you will see, there's a lot of science involved. It is fascinating to realize that this process was developed without most of that scientific knowledge that we have at our disposal now. We humans haven't (yet) been able to make such a beautifully complex product ourselves. Our artificial vanilla is a vast over-simplification of the actual product.
Scalding vanilla beans
The first step of the curing process is scalding vanilla pods, which is slightly similar to scalding milk. Scalding consists of quickly (approx. 2 minutes) dipping the beans in hot water of about 65-70 Celsius. This quick heat breaks down part of the cell structure and stops respiration, similar to when you would blanch vegetables. This helps to set free nutrients by breaking down cell walls and other cellular structures. It 'opens up' the pod for further processing.
The heat treatment also impacts the micro-organisms sitting on the vanilla pod. A lot of yeasts and moulds (which could cause spoilage) are killed. However, micro-organisms that like the heat (i.e. thermophilic bacteria) will survive. As a result, the diversity of micro-organsms is less, but the ones remaining do impact the overall vanilla quality.
Alternatively, freezing and sun drying are techniques also used to accomplish this stage of the process.
Autoclaving
After the heat treatment the pods are put in a closed off box and left to cool down for up to 48 hours. By sealing off the box the beans cool down only slowly and moisture cannot escape any further.
It's during this so-called autoclaving that the pods start turning brown instead of green.This browning is due to a common oxidation reaction. Since the pods only cool down slowly, the temperature for these and other reactions is quite optimal. Enzymes play an important role here.
Sweating & drying
Then starts a several days long cycling process in which the pods dry during the day, in the bright sunlight and during the night they are brought inside and packed in closed boxes, to sweat. The humidity during this stage can rise up to 95%.
On the one hand the beans have to be dried in order for them to be kept for long periods of time without any microbial spoilage, while on the other hand, producers will want optimal flavour development (mostly done by enzymes and micro-organisms, to a lesser extent) achieved from high humidity and high temperature. In order to strike this balance, the moisture and temperatures should be a bit more moderate. Overall, the moisture content only drops a few percentage points, but the drying step does greatly help in reducing a possible increase of micro-organism growth.
It is known that in certain curing processes bacilli micro-organisms are the most prevalent. They seem to contain enzymes that will help to break down the cellular structure (e.g. proteases, hemicellulases, cellulases and b-glucosidases). However, in other trials these enzymes were not found or to a lesser extent and the vanilla would still cure fine. These findings elucidate the complexity of the process.
Proper drying
After this cycle of sweating and drying the pods are properly dried to eliminate the risk of fungal growth and spoilage of the pods. This will easily take up to a month, depending on weather and storage conditions. In most cases drying is done outside under a roof or shelter, where the wind can assist in moving away moisture. This step is important for conservation, not as much flavour development.
Conditioning
Now we have safe, dry, vanilla pods that can be packed in bags without risk of spoilage. However, the curing process isn't yet over. This conditioning step, inside the plastic bags, is still essential for proper flavour development. It is even said that vanilla pods will continue to develop flavour even months later, when packed in their final air-tight packages.This conditioning step, again, isn't fully understood. There are so many biochemical reactions that play a role in flavour development here. To name just a few: esterification, etherification and oxidative degradation. All of this results in that rich bouquet of over 200 flavour components.
Chemistry of curing & vanilla pods
As you will realize by now, vanilla pod curing is a highly complex and labour intensive process. This is, partly, what makes vanilla expensive. We’ve mentioned previously that we do not fully understand the chemistry of vanilla pod curing, but there are some important parts that we do understand.
Vanillin is toxic for plants
Vanillin is one of the main volatile components that gives vanilla its characteristic aroma. Vanillin is toxic for the vanilla plant itself which is why it doesn't contain free vanillin inside its pods. Instead, the vanillin is present in a bound form which doesn't make it harmful anymore. The bound vanillin can be present in quantities as high as 15% of the pod's dry weight. The bound form is called: beta-D-glucoside and during curing of the pod enzymes (glucosidases) cut the vanillin loose from the bound form.
Production of vanillin in the plant
Only recently has it been found that the production of vanillin in the plant has a relatively easy pathway. There's a single enzyme that catalyzes the formation of vanillin (glucoside) from the molecule ferulic acid. The enzyme is appropriately named vanillin synthase. Even though this is a simple reaction, there are a lot of other pathways and also the ferulic acid has to be formed in a chain of reactions.
Composition of vanilla
At the end of conditioning, there are over 200 flavour components in the finished vanilla pod. The most abundant is vanillin which can be present in 2,5-4,5w%. Apart from that other important components are p-hydroxybenzaldehyde, p-hydroxybenzoic acid, vanillic acid, p-hydroxy benzylalcohol, vanillyl alcohol. It's the ratio of the components that determines overall quality. This isn't only influenced by the curing process but also growing conditions, type of vanilla plant used, among others.
Recent developments
Vanilla prices have increased considerably in the recent past. This is due to both a decrease of available vanilla due to natural challenges for growing the vanilla, but also a continuing increase of vanilla use.
As previously mentioned, a lot of the vanilla currently used in foods is actually artificial. However, with recent trends seeing consumers prefer natural ingredients, researchers are looking for ways to produce vanilla (or, more specifically, vanillin) naturally, for instance through the use of micro-organisms. Only recently did researchers figure out how vanillin is produced and by which enzyme. In the coming years this will probably result in various new ways of making natural vanilla without necessarily using vanilla pods.
A vanilla tip
Did you know that the black vanilla seeds in the vanilla pods are free of aroma? Despite the fact that they look nice in naturally flavoured vanilla dishes, they don't actually impart any flavour. On the contrary, it's mostly the inside of the vanilla bean that contains the flavour. All in all, be sure to scrape out the inside of the bean properly or let it soak nice and long for optimal flavour!
Recent developments
Stay tuned for the next post to read about the connection between whisky and vanilla.
References
Varanashi research foundation, vanilla processing and curing at farmer's level, A.K. Moorthy & V.K. Moorthy, link
Microorganisms with a Taste for Vanilla: Microbial Ecology of Traditional Indonesian Vanilla Curing, W.R.M Roling, et al, 2001, Applied and environmental microbiology, p. 1995-2003, link
Vanillin formation from ferulic acid in Vanilla planifolia is catalysed by a single enzyme, N.J. Gallage, et. al., 2014, Nature Communications, 5:4037, link
The effect of killing conditions on the structural changes in vanilla (Vanilla planifolia, Andrews) pods during the curing process, M.D. Mariezcurrena, 2008, International Journal of Food Science & Technology, Volume 43, Issue 8, pages 1452–1457, link
Comparative metabolomics in vanilla pod and vanilla bean revealing the biosynthesis of vanillin during the curing process of vanilla, Fenglin Gu1, et. al., 2017, Gu et al. AMB Expr, 7:116, link
Biotechnology of natural products, W. Schwab et. al, 2018, Springer International Publishing, chapter 1, link