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The Drinkability Index

Different Aging Algorithms
Different Consumption Types
Conclusion

This report orders the wines in the cellar by an index number which shows whether a wine is being consumed faster or slower than a rate implied by the drinking window. For purposes of simple explanation, let's assume for a moment that you wish to consume a wine in linear fashion throughout the drinking window, although in reality we can model this in more complex ways for different types of wines.

For example: you buy a case of wine with a Wine Advocate suggested twelve-year drinking window. If you get five years into the window and you still have 12 bottles, your index is positive five (5): you still have five bottles to drink. If you get five years into the window and you have consumed nine bottles, you have an index of negative four (-4): you are consuming the wine at a rate that will exhaust it before the window closes.

If you get beyond the window and you still have bottles left, the index will be a positive number greater than the number of bottles PLUS a penalty of 100 points, and it will keep increasing as time goes on. If you have not yet gotten to the start of the drinking window, the index will be a negative number that will approach zero as the start-consume date approaches. The index is dynamically calculated when the report is run based on the current date. The formula for the Drinkability Index is:

The Drinkability Index

(Days into Window) / (Total Days in Window) = % Window Used
% Window Used * (Bottles on hand + Bottles pending delivery + Bottles consumed) = Should Have Consumed
Drinkability Index = Should Have Consumed - Bottles actually consumed

EXAMPLE 1: 1994 Beringer Cabernet Sauvignon

Drink between 1997 and 2007
12/31/2007 - 1/1/1997 = 4,016 days
Today = 12/9/2003
Days used = 12/9/2003 - 1/1/1997 = 2,533 days
2,533 / 4,016 = 0.631 = 63.1%
Number purchased = 12
Number should have consumed = 12 * 63.1% = 8.2 bottles
Number in inventory = 9
Number consumed = 12 - 9 = 3
"Drinkability Index" = Should have consumed - Actually consumed = 8.2 - 3 = 5.2 (drinking too slowly)

EXAMPLE 2: 1990 Château Meyney

Drink between 1996 and 2010
12/31/2010 - 1/1/1996 = 5,478 days
Today = 12/9/2003
Days used = 12/9/2003 - 1/1/1996 = 2,899 days
2,899 / 5,478 = 0.529 = 52.9%
Number purchased = 14
Number should have consumed = 14 * 52.9% = 7.4 bottles
Number in inventory = 3
Number consumed = 14 - 3 = 11
"Drinkability Index" = Should have consumed - Actually consumed = 7.4 - 11 = -3.6 (drinking too quickly)

A few notes:

The report calculates based on 750ml equivalent. So if you open a 375ml bottle, that only counts as opening half a bottle. The actual count of bottles (if different) is still available by hovering over the various numbers.
The report breaks out pending bottles from those in stock, although all bottles are taken into account for calculating a score.
The report can be filtered by bottle size, storage location, or bin. The total number of bottles for the wine are still shown (as the drinkability score is computed on the basis of all bottles), and there is an additional indication showing the number of bottles for that specific bin, locale or bottle size.
If "Days Used" is greater than the drinking window (fallen off the far end of the window), the algorithm adds a 100 point penalty to the calculated index to emphasize the need to drink up. This can be toggled off.
By default the report calculates using the current date, but you can fill in any day of your choice to simulate time travel's effects on wine...

Different Aging Algorithms

That should give you a basic idea of the how the feature works. However, to make things more accurate we can actually calculate the % of the window consumed using richer models that reflect how the wine will age and the relatively approachability and enjoyment throughout its lifespan. So in addition to linear aging, you can imagine wines that are best on release and then fall off quickly (Beaujolais, Moscato d'Asti), wines that have two peaks of approachability for young and mature drinking (German Riesling, many Southern Rhone reds), wines that age in a bell curve and need some time to come around to their peak and then tail off over time, plus wines that are similar but take longer (Bordeaux, Rioja) or wines that are approachable after a bit of time and then fall off (many white wines). All of these are depicted on the graph below:

The way the graph is calculate and the drinkability index generated is to break the drinking window into 12 segments with different percentages of the "% Window Used" handed out for each 1/12th of the curve. So the linear example would obviously hand out 1/12th for each segment, but the other models are all skewed differently as you can see below:

The drinkability report actually allows you to choose a global algorithm for all of the wines, but by default the report actually pre-defines different algorithms for different categories of wines. Frankly, this is horribly subjective, so I am a bit worried about the amount of conflicting feedback I will get. However, I wanted to try. As of this writing, here are the rules:

LATE BELL: Red Bordeaux; Red Northern Rhône and Rioja
TWIN PEAK: Red Southern Rhône; White Northern Rhône; White German
FAST AGING: All Rose; Beaujolais; Moscato d'Asti
STANDARD BELL: All other reds
EARLY BELL: All other dry whites

Different Consumption Types

When consuming a bottle in CellarTracker you have the ability to mark it in a number of different ways such as "Drank from my cellar", "Restaurant purchase", "Gave away as a gift", "Sold or traded", "Spoiled (corked/oxidized) and returned to vendor", "Spoiled (corked/oxidized) but not returned", "Donated" and many more. However, for purposes of calculating the drinkability index many people wanted a way to focus the calculations on just bottles that they had actually consumed. So there is a pair of options to either focus on all consumption or just a few categories (Drank from my cellar, Drank by a family member, Lost or missing).

Conclusion

I hope people appreciate the tool but also understand that it is simply a tool to help you ensure you are keeping pace with your collection. Feedback is welcome, but since I am very sure that a LOT of it will be conflicting I suspect I won't be able to act on all of it.

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