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Chapter 11. Vanilla Curing
Eric Odoux
Introduction
The vanilla curing process is designed to produce an aromatically attractive and microbiologically stable product from green pods harvested before complete ripeness and which have no special aroma apart from a vague “plant” odor.
The curing techniques are of broad range, but generally involve four separate steps. Specific terms are used in reference to these steps in the different vanilla-producing countries—which are primarily Spanish-speaking in Central America (Mexico), French-speaking in the Indian Ocean region (Réunion, Comoros, Madagascar), and English-speaking (India, Uganda). Descriptions of these steps in different languages are often ambiguous and confused, further complicated by the fact that the separation between the four steps is often subjective and controversial. It is thus essential to clearly define this terminology before launching into an in-depth discussion on curing processes and their biochemical implications.
The first curing step is designed to stall pod dehiscence (especially in Vanilla planifolia G. Jackson, which is the most widely marketed species) by blocking the normal metabolic processes that take place during maturation. The most common techniques involve in suddenly inducing pod senescence, that is, “killing” the fruit (“mortification” in French). The main technique used for this purpose, which originates from Réunion, involves soaking vanilla pods in hot water—this is termed “scalding” and “échaudage” in French. In Mexico, the pods are traditionally placed in an oven or exposed to the sun, and the respective Spanish terms are “horneado” and “secado al sol.” A common English translation of “horneado” is “oven-killing,” but there is no specific term in French, while “sun-killing” is the English term for “secado al sol,” but again there is no equivalent in French.
The second step involves in maintaining the heat stored during the initial step as long as possible by placing the pods in closed crates that are as heat insulated as possible (generally with gunny sacks) so as to create conditions that are similar to those of a sweating chamber. This step is called “sweating,” or “étuvage” (from an etymological standpoint, this term introduces the notion of humid heat) in French, and “sudor de horno” or “sudado” in Spanish. These terms are more ambiguous and the interpretations may therefore differ markedly. Some authors (Bourriquet, 1954) report that during this step the pods can release a blackish fluid, which some authors explain as being due to drying associated with pod sweating. This drying conflicts with the conditions established during this step, and the phenomenon has not been experimentally assessed (Odoux, 2000; Perez-Silva, 2006). The blackish fluid is probably due to the result of excess condensation (mixed with bits of crushed pods), which is in line with the “sweating” and “étuvage” notions. Other authors (Ranadive, 1994; Dignum et al., 2001) consider that the sweating step also includes the first days of sun drying when moisture loss definitely occurs.
In the third step, the vanilla pods are dried to stabilize the product—this is called the “drying” step, or “séchage” in French, and “asolear” or “secado del sol” in Spanish. These are clear-cut terms describing the pod drying phenomenon, despite the fact that this step obviously involves more than just moisture loss—which is why it is hard to clearly separate the end of the sweating step from the beginning of the drying step. Moreover, “asolear” and “secado del sol” introduce the notion of sun exposure as a pod-drying technique.
The fourth step is termed “conditioning,” and “conditionnement” or “affinage” in French, and “afinado” in Spanish. These terms pool two complementary notions, that is, packaging, storage, and preservation of the product in a heat-tight atmosphere, with the aim of promoting “aromatic maturation” overtime.
This chapter highlights how these techniques and their derivatives ultimately involve in maintaining vanilla pods in high temperature and humidity conditions as long as possible in order to set the stage for a number of enzymatic and chemical reactions that promote the development of the aroma typical of vanilla, while curbing microorganism proliferation (especially molds). However, as discussed here, this curing is a rather continuous process, thus hard to separate into clearly defined steps.
CONVENTIONAL CURING TECHNIQUES
STEPS 1 AND 2: INITIAL HEAT TREATMENT
In V. planifolia G. Jackson, heat treatment is mainly carried out to hamper pod dehis-cence (n.b. Vanilla tahitensis is not subjected to heat treatment because it is not a dehiscent species, see also Chapter 13), which would reduce the market quality of vanilla pods. The pods are voluntarily harvested before the ripeness stage at which dehiscence occurs, but this early harvesting does not stop the process. Different techniques have thus been developed to stop it completely. These techniques are compatible with the way vanilla is cured under local conditions in producing countries, that is, where technical resources are often very limited.
In the first step, the most common technique implemented in the Indian Ocean region (Madagascar, Comoros, Réunion, etc.) involves soaking green pods in a water-filled tank heated over an open fire (scalding process) (Figure 11.1). Then the second step involves placing the pods immediately in covered crates to avoid heat loss (sweating). In theory, scalding should be carried out for 3 min in a water bath at 65°C, while the sweating process takes 24 h. In some countries, the scalding time and temperature are adjusted according to the pod grade, so the pods are sometimes presorted.
FIGURE 11.1 Killing step: green beans are soaked in hot water.
In practice, these two steps are carried out in a variety of ways. For instance, in Madagascar, which is the top vanilla-producing country, many operators are involved, ranging from farmers who produce just a few hundred grams of vanilla beans to exporters who deal with hundreds of tons of this product, and the technical resources available to these operators also differ markedly (Odoux, 1998). Most farmers have no way to control the scalding temperature and time, which means there may be substantial variations in the treatment process. The quantity of pods cured, which may vary considerably between operators, can have a great impact on the heat treatment quality (e.g., edge effects in crates). The sweating process can also be extended for up to a few days if the climatic conditions are unsuitable to start the drying step. In Réunion, where almost all of the vanilla crop is processed in two centralized units (a cooperative and a private company), the scalding and sweating processes are carried out twice to achieve a uniform heat treatment (Odoux, 2000). However, little is known about the actual impact of these alternatives on the end quality of the vanilla.