Four things to taste

In this model, tasting a bottle gives her exactly four things.

A real palate notices far more than four, of course. The model gets four because four is small enough to follow all the way through.

The wine world is being shrunk too. There are thousands of grapes and hundreds of tastes. This chapter uses two grapes and two tastes, and every bottle is made from a single grape. Real wine is not this tidy, and none of what follows depends on it being tidy. It is simply easier to watch learning happen when there are four numbers to watch instead of four thousand.

Here are the four units:

Each unit holds one number. That number says how strongly she detects that sensation when she tastes. The number is never smaller than 0 and never larger than 1.

A 0 means she detects none of it. A 1 means it is unmistakable.

These numbers are not facts hiding inside the bottle. They are a record of one tasting. One person might rate the apricot at 0.3, while another rates the same wine at 0.6.

Once one tasting has been written down for this example, the pricing model treats those four numbers as fixed. This chapter begins there. It studies how the model learns from the supplied numbers, not how a taster or measuring device produced them.

The two grape units are always 0 or 1, never anything in between. Every bottle here is made from a single grape, so one of these two units is 1 and the other is 0. If cabernet is 1, viognier is 0. If viognier is 1, cabernet is 0. There is no bottle in this chapter that is half cabernet and half viognier.

The two taste units can be anything from 0 to 1. This is the real difference between them and the grape units. A wine can come across as faintly plummy, or strongly plummy, or anything in between. So plummy might be 0.3 for a faint plum taste, or 0.9 for a very strong one.

Here is one possible tasting record. A cabernet that tastes strongly of plum, with no apricot at all:

cabernet 1, viognier 0, plummy 1, apricotty 0

Or [1,0,1,0] in compact form. The four numbers are always in the same order: cabernet, viognier, plummy, apricotty.

Now return to the bottle waiting for us. It is also a cabernet, but its plum taste is only half strength:

cabernet 1, viognier 0, plummy 0.5, apricotty 0

Or [1,0,0.5,0].

This is the first bottle the model will actually price.

Look at the third number. 0.5 means the plum taste is half strength. Remember it. It matters later.

So that is what arrives from a bottle. Four numbers, and nothing else.

But four numbers about a wine are not a price. Something has to turn them into dollars.