Handbook of Vanilla Science and Technology

Although we can associate floral notes to anisyl compounds, smoky and phenolic notes to guaiacol and p-cresol, tobacco-like character to nicotine derivatives, sweet notes to vanillin and its derivatives, or balsamic notes and resinous character to higher molecular weight diketones, far more work needs to be done to correlate aroma chemicals identified in a particular vanilla bean type to its peculiar aroma and taste. Black (2005) has identified many known aroma chemicals in cured vanilla beans of different geographic origins and species. His work seems to indicate how the preponderance of certain chemicals in each case determines the overall flavor character of those beans. Black’s work shows strong correlation between butter notes and the presence of diacetyl and acetoin, between guaiacol and p-cresol and strong phenolic notes, between pentanal, hexanal, and the green notes, between limonene, nonanal, decanal, and citrus notes, between vanillin, methyl cinnamate, t-caryophyllene, and typical vanilla, balsamic, woody notes.

9.2.3 Moisture content of vanilla beans

The moisture content of commercial vanilla beans varies from 10% for poor quality lower grade beans to 35% for gourmet beans. The extraction grade beans contain from 20 to 25% moisture, the maximum limit set by the US standard of identity. Drier beans are less aromatic and less appealing than supple, shiny, high moisture beans. However, under poor handling and storage conditions, the high moisture beans can easily develop mold.

Moisture content in vanilla beans can be determined by using the following methods:

• Hot Oven Method.

• Vacuum Oven Method.

• Infrared Heating Method.

• Chemical Methods.

― • Distillation with toluene.

― • Karl Fischer method.

9.2.4 Vanillin content

Vanilla derives its flavor character and flavoring strength from one of its most important components, vanillin. Almost one-third of the flavor strength of a vanilla product is attributed to its vanillin content. Naturally, one of the criteria for determining the vanilla bean price is its vanillin content. Beans with higher vanillin content fetch a higher price.

The vanillin content of cured vanilla beans of different geographic origins varies considerably, from trace quantities to almost 3% by weight. However, this is the function more of cultivation and curing practices than of the geographic location. Beans harvested at full maturity and cured under properly controlled conditions yield highest vanillin. Fully mature beans, if cured poorly, can produce very low vanillin. On the other hand, immature or under matured beans will produce low or no vanillin, even if curing is carried out meticulously. Gassenmeier et al. (2008) note that vanilla beans produced using alternative vanilla-processing methods (as opposed to traditional curing method) can produce beans with higher vanillin content but can be poor in overall aroma characteristics.

Vanillin content of different species of beans is significantly different. Beans of

V. planifolia can yield 2 to 2.5% vanillin under optimum conditions, whereas beans of

V. tahitensis normally will produce no more than 1.2 to 1.5% vanillin, even under optimum conditions.

Standardized methods for vanillin quantification from beans are:

9.2.4.1 Vanilla bean extraction

Weigh 50 g of dry cured beans. Cut into quarter inch length pieces, place in a 500 ml Erlenmeyer (conical) flask, add 250 ml of 35% aqueous ethanol, and close the flask with a stopper. Place in a hot water bath maintained at 55 to 60°C for at least 8 to 12 hours, shaking the flask once every hour. Then decant the extract and collect it in a 500 ml volumetric flask.

Add 250 ml fresh solution of 35% aqueous ethanol to the Erlenmeyer flask containing extracted beans, close with the stopper and place in the hot water bath for another 8 to 12 hours, shaking the flask occasionally. At the end of this period, decant the extract and add to the volumetric flask containing the first extract. Bring the volume of the combined extract to 500 ml with the addition of 35% aqueous ethanol, if required. Shake well. This is equivalent to one-fold vanilla extract.

9.2.4.2 Vanillin determination

9.2.4.2.1 UV (Spectrophotometric Method)

Standardization of 1 ppm vanillin. This is done every 3 to 6 months.

Dissolve 0.1000 g vanillin in 3 ml 190 proof ethyl alcohol in a 100 ml volumetric flask and bring to volume with distilled water.

Prepare 0.1 N sodium hydroxide (NaOH) solution by dissolving 4g NaOH pellets in distilled water and bringing the volume to 1 liter in a 1-liter volumetric flask.

Pipette 3 ml vanillin solution into a 1-liter flask, add 2 ml of 0.1 N NaOH and bring to volume with distilled water.

Prepare a blank by adding 2 ml 0.1 N NaOH in a 100 ml volumetric flask and bring to volume with distilled water.