Wednesday, May 27, 2015

Short- and long-term implications of US-Cuba travel liberalization for Caribbean tourist destinations

My friend recently bought a vacation home on the Jamaican north coast and, as a result, we have been making the trek between MCO and Norman Manley Airport with some frequency. On my last trip over, I happened to have a window seat (a fate second only to having a middle seat) and noted the broad expanse of Cuba as we traversed its airspace. And that set me wondering. With the recent opening to Cuba announced by President Obama, it is conceivable that a fuller liberalization will follow sometime in the the future. What then would be the impact of such liberalization on non-Cuba Caribbean tourism, in general, and Jamaican tourism, specifically. My curiosity was piqued so I set out to investigate.

According to the Jamaican Tourist Board (, there were 25 million tourist arrivals in the Caribbean in 2013, a 1.8% increase over 2012. The United States was the most important contributor, with 12.3 million of its citizens having travelled to the region in that timeframe, up 2.9% over 2012. The percentage distribution of visitors to the region is shown below.

Percent of Total
South America

The three most visited islands, ranked by frequency of visit, are Dominican Republic, Cuba, and Jamaica (It should be pointed out that Cuba is second in the ranking even though it had less than 100,000 US visitors in 2013.). Jamaica itself had 2 million stopovers in 2013, 1.8 million of whom were foreign and the remainder non-resident Jamaicans. One million of these visitors came for "liesure, recreation, and holiday."

Cuba had 2.8 million visitors in 2013 with a total spend of $2.3 billion (Jessop). Of the visitors, 92,000 were from the US (the 350,000 - 400,000 Cuban-Americans who visit Cuba annually are not included in these numbers).

Just to review, the recent Obama initiative allows the following (
  • Americans can visit Cuba for any of 12 reasons without having to obtain a special government license
  • American travelers to Cuba can bring back up to $400 worth of goods inclusive of cigars and liquor
  • Travelers can now use their debit and credit cards on the island
  • US financial institutions can open accounts at Cuban banks and enroll merchants there.
Jessop sees a number of short-term implications associated with this opening:
  • Increasing pressure on available hotel rooms
  • A concomitant upward trend in currently low-priced room rates
  • Increased investment in the hotel sector by foreign companies
  • Pressure from US legacy carriers to fly scheduled services to Cuba out of the US
  • The increased attraction of sailboats into the recently constructed Cuban marinas
  • Increasing number of calls by cruise ships
  • Rapid diversification and decentralization of Cuba's tourism product.
But these implications are associated with the current Obama initiative. A number of economists have been studying the issue of a complete elimination of the US tourist barriers -- a not-inconceivable development, given where things are headed -- both in terms of its implications for Cuba as well as for its neighbors. In commenting on Padilla's projection of the Cuban tourism industry post-Castro, Crespo estimates that his forecast of 3.2 million additional US visitors to Cuba annually would require:
  • Betweeen 98,000 and 116,000 additional hotel rooms at a cost of between $4.3 and $5.7 billion
  • Additional uplift capability to carry those visitors.
According to Crespo, it would take between 17 and 22 years to build an additional 58,000 - 76,000 rooms and this factor alone ensures a non-apocalyptic increase in US tourism to Cuba.

Romeu, in an IMF Working Paper, used a  gravity trade model to assess the outcome of US travel liberalization. His findings were as follows:
  • Liberalization would increase overall visitor arrival to the Caribbean by between 2 and 11%
  • The current budget-conscious, adventure-focused OECD visitor will be displaced by the US visitor who has lower transportation costs and demands higher levels of service
    • It is likely that these tourists will select destinations with which they might have had a former colonial relationship or some language or other cultural affinity
  • There will be a loss of US tourists for the other Caribbean countries but their losses will be offset somewhat by the redirected OECD tourists
    • Spend will be at lower levels though given the type of tourists being redirected
  • Strong tourism growth awaits some destinations while others face potential long-term decline

In the short-term, there will be a slow but steady increase in the number of US tourists visiting Cuba. Given the constraints imposed by the President, these trips will most likely be taken by culture warriors, not a core constituency for the Caribbean tourist market. In addition, these trips will be one-offs; "I was there while the country was still unspoiled."

In the longer term, however, there are significant risks for Cuba's neighbors. Its attractiveness is reinforced by the fact that it is the second-most-visited Caribbean country, even with a paltry amount of US tourists. If tourism were liberalized, and even if a large amount of US tourists visiting Cuba were first-time Caribbean visitors, there would still be some siphoning-off of "Caribbean regulars." So it is likely that Jamaica, for example, would see a decline in its US-origin visitors. And I would propose that it would be a consistent drop over a number of years as some percent of those visitors seek to "try-out" Cuba. The country would have a significant additional competitor for the US tourist dollar. And the pool of redirected OECD numbers will be split between the countries and, in addition, the per capita spend of each individual will fall below the per capita spend of the US tourist. The financial implications are evident.

In order to compete in this marketplace, the countries will have to focus on customer attraction and retention. Customer attraction will revolve around giving first-time visitors a reason to come. Cuba is a large country with a diverse array of experiences to offer to the tourist. These countries will have to map out points of interests and activities to get customers to visit their countries and to stay. For example, I have been visiting Jamaica for years now and have never been to Port Antonio. I visited there on my last trip and was blown away by the history of the area, the available activities, and its place as the home of the jerk style of cooking. These countries will have to do a better job of providing a more fulsome picture of the available areas of interest (in addition to the sun and sand and rum).

In terms of customer retention, the folks at Disney and Universal are constantly adding to the palette of attractions, giving visitors a reason to come back to Orlando again and again. These countries will have to adapt that mentality and constantly be on the lookout for additions to the "attractiveness" portfolio.

One of the reports that I read suggested that these countries partner with Cuba in order to develop packages where someone could spend three days, lets say, in Cuba and two days in another country. I do not see this happening. Cuba can easily support a tourist over seven days with the diversity in its environment and it would have no incentive to partner with these smaller countries. What would those countries bring to the table that would be of interest to Cuba when Cuba has the tourist sitting behind the wheel of a 1959 Dodge in Havana? I can't see it.

David Jessop, Cuba and Carribean Tourism,, 1/9/2015
Havana or bust: How US-Cuba Realtions will impact Tourism, knowledge,
Nicolas Crespo, Comments on "The Tourism Industry in the Caribbean after Castro" by Padilla,
Rafael Romeu, Vacation Over: Implications for the Caribbean of Opening US-Cuba Tourism, IMF Working Papaer, 7/2008.

©Wine -- Mise en abyme

Tuesday, May 26, 2015

Enzymic oxidation of wine must

In my most recent post, I initiated a series on wine faults with a discourse on sulfur taint in wine production. I continue in that vein with a discussion of must oxidation.

Wine oxidizes when exposed to air via two primary mechanisms: enzymic and non-enzymic oxidation. Enzymic oxidation primarily afflicts wine must and requires the presence of the enzyme Tyrosinase (or Lacasse, in the case of botrytized must), phenolic compounds (flavonols, anthocyanins, tannins, etc.), oxygen, and metallic co-factors (iron, copper, etc.). Non-enzymic oxidation, also known as chemical oxidation, occurs in two steps: (i) Oxygen in the air reacts with wine phenols to create hydrogen peroxide and (ii) hydrogen peroxide reacts with ethanol to form acetaldehyde. The effects of oxidation on wine are browning, loss of fruity aromas, and aldehydic aromas. Because of these characteristics, oxidization is widely viewed as a wine fault.

Enzymic oxidation (which primarily afflicts wine must) requires the presence of the enzyme Tyrosinase* (or Laccase**, in the case of botrytized must), phenolic compounds (hydroxycinnamic acids, with the main player being caftaric acid but others — including coumaroyl, tartaric acid, and catechin — as alternates) to perform the role of substrate, oxygen, and metallic co-factors (iron, copper, etc.). These enzymes interact with the substrates to form caftaric acid quinone which, in turn, reacts with glutathione (normally a powerful anti-oxidant) in the must to form Grape Reduction Product (GRP). The conversion of the oxidized quinone to GRP limits the browning of the juice to some extent (duToit and Kritzinger). Once the glutathione is depleted, the remaining caftaric acid quinone reacts with other must constituents to form caftaric acid and begins the oxidation process anew. Browning occurs when the flavanols oxidized by caftaric acid quinones polymerize and precipitate out. Unlike the case of wines, these brown pigments are insoluble in must.

Because tyrosinase is associated with grape solids, its enzymic activity is significantly diminished once the solids have been removed from the equation. Laccase is difficult to eliminate from grape juice.

The activity of these enzymes will be impacted by (Boulton, et al, Principles and Practices of Winemaking):
  • The concentration of major phenols
  • Competition between substrates for binding and reaction
  • The caftaric and glutathione content of cultivar (the state at which glutathione is depleted will determine the level of potential browning)
  • The ascorbic acid content
  • Temperature
  •  Wine pH.
Both tyrosinase and laccase use catechin, anthocyanin, flavanols, and flavanone as substrates but, as indicated in Table 2.1 of Boulton et al., laccase acts on a far wider range of substrates than does tyrosinase. UCDavis pegs the added scope of laccase as encompassing anthocyanin pigments and ascorbic acid, the latter of which is itself used as an antioxidant

A number of suggestions have been advanced to impede/control the oxidative activities of the enzymes:
  • Boulton has reported that the addition of sulfur dioxide at levels between 25 and 75 mg/L will reduce tyrosinase activity between 75 and 97%. This inhibition may be the result of a binding of a sulfhydril group on the enzyme or a bisulfite inhibition resulting from the interaction of sulfites and intermediate quinones. (Sulfur dioxide does not significantly impact the operation of laccase (addition of 150 mg/L sulphur dioxide yields only a 20% reduction in oxidative activity); as a matter of fact, it can serve as a substrate. The only way to completely stop laccase is to use HTST to denature it.) Sulfur dioxide can reverse the effects of oxidized quinones to colorless phenols. Sulfites react slowly with oxygen, but react with important intermediates (hydrogen peroxide, acetaldehyde, quinones)
  • Judicious harvesting, crushing, pressing to minimize enzyme reaction subtrates and limit oxygen exposure
  • Bentonite fining to remove the enzyme
  • Hyperoxidation to reduce phenols
  • Use healthy grapes
  • Keep wine containers full
  • Use of inert gas to limit oxygen contact
According to Boulton et al., ascorbic acid can be used as an antioxidant either alone or in cooperation with sulfur dioxide. It does not have any direct effect on the enzyme but it reduces the potential for browning by consuming the available oxygen. It can also delay the onset of browning by converting quinones back to the original phenol. The recommended levels of ascorbic acid addition ranges between 50 and 200 mg/L. Ascorbic acid will react with oxygen to form dehydrascorbic acid and, upon the consumption of the former, browning may be initiated. Conversely, unused ascorbic in finished wines can act like a phenol, leading to the production of acetaldehyde where oxygen is introduced.

*Tyrosinase is located in the chloroplasts of the grape berry cell membrane and, in the must, is predominantly attached to grape particles. Its concentration in the must is dependent on the variety and the maturity of the fruit. Warmer temperature and higher pH increases the activity of this enzyme.

**Laccase is generally associated with Botrytis and can cause bunch rot and grey mold in grapes. Moisture on the berry surface can cause infection. Farming and harvesting practices can impact the levels of rotten fruit brought into the cellar and, potentially, included in the must. This enzyme is considered more dangerous than tyrosinase because it oxidizes a wider range of phenolic compounds and is resistant to sulphur dioxide. As is the case for tyrosinase, this enzyme is more active at higher temperatures and pH.

©Wine -- Mise en abyme

Tuesday, May 12, 2015

Sulfur taint in wine production: Genesis and exodus

A winemaker is continuously on guard to ensure the earliest possible detection of issues that could have potentially negative effects on the quality of in-process or finished wine. One issue that is treated with the utmost respect, and attended to with some alacrity, is sulfur taint, the primarily olfactory manifestation of sulfur compounds in the wine. Sulfur taint is the bane of the winemaker because ( Lansing, Wine defects during fermentation, Wine Business Monthly, April 2011):
  • It is generally associated with negative aromas
  • It has a low threshold for sensory detection
  • It has high chemical reactivity
  • It is difficult to mask and/or remove.
The sulfur compounds associated with sulfur taint, and the population of odors associated therewith, are illustrated in the figure below.

In this post I will examine the origins of sulfur in must, the creation of sulfur compounds during winemaking, and strategies for minimizing the incidence and/or removing these compounds from the medium.

Sulfur taint has its origins in either the vineyard, the cellar, or both. In the vineyard, elemental sulfur is sprayed on the vines to combat the potential effects of powdery mildew. If this spraying is conducted too close to harvest, portions of the sulfur will remain on the grapes and make its way into the fermentation process. An example of sulfur-like off odors created in the cellar is the case of hydrogen sulfide production by the yeast to synthesize the sulfur-containing amino acids methionine and cysteine. This process is facilitated by the reduction of sulfates via the sulfur-reduction pathway. A lack of intracellular nitrogen will not curtail the process and the excess hydrogen thus created cannot be incorporated into the amino acid. Rather, it is secreted into the medium (Kennedy and Reid, Yeast nutrient management in winemaking, The Australian and New Zealand Grapegrower and Winemaker, 537, October 2008).

A listing of the sources of sulfur-like off odors is presented in Table 1.

Table 1: Sources of sulfur taint in wine production.
Environment Source Action Impact
Vineyard Elemental sulfur
used as fungicide 
Reduction during fermentation

Sulfur-containing pesticides do.

Excess of metal ions 

Vine stress

Unsound fruit


Cold soaking

Growth of yeasts such as Kloeckera

Depletion of amino acids and micronutrients

Native Yeasts High hydrogen sulfide production Compete against other yeasts for dominance of fermentation

Excess hydrogen sulfide from sulfate reduction Hydrogen sulfide used to synthesize  Absence of nitrogen causes produced hydrogen sulfide  to be secreted into the medium

High levels of sulphur dioxide added to must at crush Allows sulphur dioxide to bypass the sulfate reduction system Sulfur dioxide enters the yeast cell directly

Vitamin shortage in high YAN musts

Nitrogen limitation Produces sulfur-like off odors Production begins 30 minutes after ammonia starvation initiates
Source: Compiled from Lansing and Kennedy and Reid)

The timing of the production of sulfur-like off odors is shown in Table 2 below.

Table 2. Production timing of sulfur taint by sulfur class.
Sulfur Class Production Timing Source
Hydrogen Sulfide Early in fermentation (2 - 4 days) Nitrogen/vitamin deficiency

Fermentation end Degradation of sulfur-containing compounds

Sur lie aging Autolysis

In bottle Generally under screw cap
Higher Sulfides Late in fermentation/Sur lie aging Release of compounds by metabolically active yeasts

Degradation of sulfur-containing amino acids

Degradation of cell compounds during autolysis
Source: Compiled from Lansing

There are a number of precautionary steps that can be taken to minimize the potential for sulfur taint (Lansing; Kennedy and Reid):
  • Minimize the use of sulfur in the vineyards and cellar
    • In the vineyard, ensure adequate time spacing between application and harvest
  • Press stressed fruit separately
  • Provide adequate nutrition to support the yeast during alcoholic fermentation
    • The less assimilable nitrogen in the must, the greater the production of hydrogen sulfide
  • Keep yeast cells suspended in the tank during fermentation
    • Allows an even distribution of fermentation
    • Allows the yeast full access to distributed nutrients
  • Manage fermentation temperatures
    • Hydrogen sulfide tends to form more commonly in hot, fast fermentations
  • Mix the tank contents to prevent stratification
    • An especial risk in tall, narrow-diameter tanks
  • Remove wine from lees at the first hint of trouble
  • Smell, smell, smell.
In the cases where the odors are manifested in the wine, remedies include (i) blowing it off through volatility; (ii) inert gas sparging; (iii) precipitating with copper additions; and (iv) fining.

©Wine -- Mise en abyme

Wednesday, May 6, 2015

Non-Nitrogen yeast nutrition requirements during alcoholic fermentation

In addition to their utilization of nitrogen as a nutrient during alcoholic fermentation (AF), yeasts synthesize and/or assimilate a number of factors (growth, co, and survival) that help them compete and survive in the hostile environment that is the active fermentation vessel.

Vitamins are growth factors involved in yeast metabolism with some of the needed species synthesized while others are obtained from the juice/must. The most important vitamins in the AF process are indicated in the table below.

Vitamin Characteristics
Biotin Plays an important role in sugar, nitrogen, and fatty acid metabolism
Yeasts cannot grow without biotin (low concentrations will support growth but 10 microgram/L optimal)
Supplementation of musts with biotin increases the viable yeast population and increases fermentation rate
Thiamine Deficiency leads to accumulation of various products including pyruvic acid which is responsible for much of the non-acetaldehyde sulfite pool
Pantothenate Involved in the biosynthesis of the sulfur-containing amino acids cysteine and methionine
Involved in the formation of acetyl Co-A (acetate donor in esterification)
Deficiency results in increased hydrogen sulfide production as well as higher concentrations of acetic acid and glycerol (the latter two producing negative results when coupled)
Pyridoxine Involved in the biosynthesis of the sulfur-containing amino acids cysteine and methionine
Deficiency results in increased hydrogen sulfide production
Source: Kennedy and Reid

Adequate levels of vitamins are normally available to the yeasts but, in some cases (mold infestation, excessive diammonium phosphate addition), a deficiency is recorded and supplements are required. Inactivated yeasts are an excellent source of vitamins.

Yeast cell membrane integrity will be affected by the toxicity of ethanol and the increase in permeability associated with higher ethanol levels will have a negative impact on sugar and amino acid uptake. So-called survival factors, comprised primarily of sterols and long chain fatty acids, are responsible for cell membrane integrity and fending off the ethanol effects until fermentation is complete. Survival factors are formed only in the presence of oxygen and grape musts normally contain enough dissolved oxygen which, when combined with the use of active dry yeast, allows the synthesis of adequate amounts of these factors.

If ascorbic acid is added to the must for any reason, no additional survival factors will be synthesized. Naturally occurring sterols and fatty acids will be depleted by excessive must clarification. In the case of a deficiency of these survival factors, the addition of inactivated yeast cells or yeast hulls will provide a rich source of sterols and fatty acids. Such additions should be adde at the beginning of fermentation and should utilize fresh material to avoid the negative effects associated with lipid oxidation.

Minerals are used as co-factors in enzymatic reactions in the yeast cell with the most important ones being magnesium, potassium, manganese, zinc, iron, and copper. The grape must normally contains adequate levels of these minerals to support AF to its conclusion.

©Wine -- Mise en abyme

Tuesday, May 5, 2015

Nitrogen as a yeast nutrient in alcoholic fermentation

Wine is a result of using yeasts in an anaerobic (oxygen-free) environment to convert sugars from pressed grape juice into ethanol in the two-step process illustrated in the figure below. The first step -- glycolysis -- results in the 6-carbon glucose being split into two 3-carbon pyruvate molecules. In the next step --- alcoholic fermentation (AF) - four atoms of oxygen and two atoms of carbon leave the pyruvate, resulting in acetaldehyde, which is subsequently converted into ethanol.

Alcoholic fermentation (Source:
According to Fugelsang (Overview of yeast selection and malolactic fermentation on aroma, flavor and phenols), the yeasts (i) extract compounds from the solids in the must/juice in order to form the "characteristic metabolites of fermentation (alcohols, esters, fatty acids, carbonyls, etc.) and (ii) cleave cysteine-containing precursors such that volatile thiols (aroma component of several varieties) can be released. The yeast that receives most of the credit -- and does most of the work -- in alcoholic fermentations is a species called Saccharomyces cerevisiae (SC) which is "specialized in metabolizing media with high sugar content and small quantities of nitrogenous compounds" (Suárez-Lepe and A. Marota, New trends in yeast selection for winemaking, Trends in Food Science and Technology 23 (2012), 39-50.). Yeasts require nutritive support to allow the performance of the above functions in the hostile environment (ethanol-rich, acidic) of the fermentation tank. It is the nitrogenous aspect of that support that is the focus of this blog post.

Proteins are used by the yeast as (i) enzymes for the glycolytic pathway (indicated above), (ii) permeases in the cell membrane responsible for the transportation of compounds into the cells, (iii) cellular constituents (Kennedy and Reid, Yeast nutrient management in winemaking, The Australian and New Zealand Grapegrower and Winemaker, 537, October 2008). These proteins are synthesized by the yeast and nitrogen (N) is a key component in that process. According to Kennedy and Reid, "Efficient protein synthesis is needed for efficient sugar transport and overall yeast metabolism."

According to Schwarcz and Schoeninger (Stable Isotope Analysis in Human Nutrition, Yearbook of Physical Anthropology 34, pp. 293-321), almost 100% of exchangeable nitrogen is found in the atmosphere or dissolved in the world's oceans and is transferred from these environments into the biological system through the processes illustrated in the figure below.  Grape vine plants receive their nitrogen through this terrestrial nitrogen cycle.

The nitrogen content of grapes are affected by variety, rootstock, climatic conditions, soil composition, vineyard management practices, fertilization, irrigation, rot incidence, and grape maturity (Kennedy and Reid). The yeast cells extract yeast assimilable nitrogen (YAN) from the grape must in the form of ammonia (preferred source of nitrogen for yeast growth as most easily assimilated) and amino acids and these are stored in the cell walls for later use. This extraction and storage of YAN is front-loaded in the AF process.

Nitrogen is required throughout the fermentation process with larger amounts being utilized during the exponential growth phase of the yesats and small amounts during the stationary phase. In some cases the grape must does not provide adequate amounts of assimilable nitrogen and is supplemented by added nitrogen in the form of diammonium phosphate (DAP). Juice levels of < 25 mg/L ammonia or < 150 mg N/L (measured as YAN) is considered nitrogen-deficient (UCDavis). Insufficient nitrogen can result in sluggish/stuck fermentations or sulfide formation (sulfur-like off-odors, mercaptans, and sulfur-containing acetic esters; the less assimilable nitrogen in the must, the more hydrogen sulfide will be produced). Supplements are best added incrementally and proportional to yeast growth (UCDavis).

Excessive nitrogen in the must can lead to elevated levels of ethyl carbamate (a supposed carcinogen) or urea excretion. The levels of nitrogen required for a successful AF is dependent on (Kennedy and Reid):
  • Initial must YAN
  • Yeast strain
  • Fermentation temperature
  • Initial grape sugar
  • Other factors.
Amino acids are the building blocks of proteins and, when brought into the yeast cell, can be incorporated as is, transformed into a different amino acid, or broken down as a source of nitrogen or sulfur. The amino acids taken up by the yeasts from the grape must is primarily stored in the vacuole to be used for protein synthesis during yeast growth. Once access to inorganic nitrogen becomes difficult, the yeast begins to break down the stored amino acids to provide nitrogen for protein synthesis. The most important amino acids taken up by the yeasts are shown in the table below.

Amino Acid Characteristics
Proline Not metabolized appreciably by yeasts under winemaking conditions
One of the predominant amino acids along with Arginine and Glutamine
Main amino acid from low-fertilization vineyards
Arginine One of the predominant amino acids
Breakdown results in formation of urea and ammonia (During wine storage, urea can react with ethanol to form ethyl carbamate, a carcinogen).
Located mostly in grape skin so processing practices could influence content in juice
Main amino acid from low-fertilization vineyards
Glutamine One of the predominant amino acids
Favored by yeasts because it can be broken down to glutamate and ammonia

The less-important amino acids taken up by the yeast cells are alanine, serine, and theronine.

©Wine -- Mise en abyme