That was the question motivating some research I conducted with a couple co-authors that is forthcoming in the journal Ecological Economics. A lot of the previous research in this area had simply interviewed people at farmers markets and asked why local food was desirable. This sort of approach is problematic for a number of reasons. For one, people at farmers markets are not a random sample of the population and likely have different preferences and desires than the average consumer. Another problem: we don't always know why we do what we do even though we're good at making up post hoc stories.
To address these challenges, we conducted some research with a randomly recruited group of German consumers (located in Bonn Germany) who spend real money to buy real food. Our research strategy was to pick two different kinds of foods for which freshness is related to distance traveled for one but not another. The idea is that this would let us sort out the extent to which desires for freshness are driving desires for local food. We picked apples (where distance traveled is related to freshness) and wine (where distance traveled is not related to freshness) and asked how much people were willing to pay (WTP) for different apples and bottles of wine that had traveled different distances.
Here is our key result:
These findings imply that ‘a mile is NOT a mile’. The data in Fig. 1 and Fig. 2 indicate that discounts for km traveled (especially in percentage terms) are higher for apples than for wine — a fact that suggests freshness is one driver of demand for ‘local’. In fact, comparing the change in bids across apples and wine suggests that of the total drop in WTP that occurs from moving from 20 to 1000 km, about 28.5% can be attributed to freshness (i.e., (1 − 0.35 / 0.49) ∗ 100 = 28.5%). In the following we will present additional evidence that people perceive freshness to be more related to distance traveled for apples than wine . . .