Sunday, January 17, 2010

Seasonal update

As I'm back in New Zealand and haven't been here since the beginning of the growing season, one of the things I did was catch up on growing degree day (GDD) accumulation for Lincoln, Canterbury.

The concept of heat accumulation (one way of measuring which is GDD) and how plant growth corresponds with it is an important tenet of modelling the phenology, or seasonal development of plants, and in this case, grapevines.

It goes a little something like this:

Plants need heat to grow. At its most basic, this is because the enzymes that do the chemical work in plants can't function when it gets cold (in fact, this is true for animals as well -it's one of the reasons cold blooded animals hibernate in the winter. Warm blooded animals use energy to generate heat, which keeps the enzymes working). So below a certain temperature threshold, plants won't grow. As the temperature rises above that threshold the enzymes work faster and faster, up until the temperature gets so high as to prevent the enzymes from working again (around the mid 30s in celcius).

So measuring the accumulation of heat during the growing season results in a pretty good match of how far along the vines have come, or what stage they have gotten to. One question, though, is what do you set the temperature threshold at?

Based pretty much on enzyme activity in relation to temperature, 10C is the most commonly chosen base temperature (the temperature below which there is no plant-active heat accumulation). However, this may differ for different types of plants, and even for different times of the season (e.g. it seems that for the process of budbreak, a base temperature of 4C is omre appropriate, and for the first leaf appearances, 7C, Moncur et al. 1989).

Setting aside those special circumstances, a pretty straightforward way to quantify heat accumulation is to take the average temperature for a month (which falls within the growing season) and if it is greater than 10C, subtract 10 from it. That result is then multiplied by the number of days in the month, which gives the number of growing degree days for that month:

[ (average temperature for the month-10) * (number of days in the month) ] = GDD

In other words, on average each day was X amount over 10 degrees, and over the whole month, X times the number of days equals the amount of plant-useful heat that was experienced. Note that negative GDDs are not counted (though it's cold, the plants don't regress - they just sit there until it warms up again)

So to put some numbers in there, if the average temperature of November was 12.6C (as it was at Lincoln in 2009), 2.6C times the 30 days in the month equals 77 GDD accumulated.

If this value is calculated for each month of the year, we can follow the heat accumulation in a useful way, especially when comparing one year to another, or comparing on location to another.

In the case of the former, the graph for the 2009-2010 season looks like this, given the data collected up through November:

Growing degree calculations for the 2009-2010 season (up through November, the orange line) and for the long term average (LTA, the blue line), which is the average over the last 40 years.

The Long Term Average (LTA, blue) is the smooth sigmoidal curve, which signifies that heat accumuation is slower (the line is more horizontal) in the spring and autumn, and quicker (an more vertical line) during summer. The number in parentheses is the LTA GDD accumulation for Lincoln - a paltry 924GDD.

You can see that up to this point in the season, the orange line (current season) is below the LTA line, which means that the season has been cooler than average. If you squint just right, you can make out that the last orange dot corresponds to 77GDD, which is what we calculated above. This also means that there was no accumulation of plant-useful heat in October, or earlier in the season (at least, when based on monthly averages - more on that in another post!).

If you want to compare seasons, this way of looking at the data is fine, but if you want to see the differences more clearly, you can plot the current season's GDD relative to the LTA, which looks like this:

Growing degree calculations for the 2009-2010 season (orange) and for the LTA (the blue line, which is the X-axis). This figure is showing the same data as the previous one, but in a slightly different way.

Now it is pretty plain to see that we're veering away from the LTA. If the line is below zero (the LTA blue line), then there has been less heat accumulation than the LTA, and if it's above, there has been more, and it's been a warmer season.

You can also see more clearly what's happening for each month. If the line moves down, then the month has been cooler than LTA; if it slopes up, then it's been warmer. If the line is parallel to the LTA, then the average temperature for the month has been the same as the LTA.

So what we'd like to see is the line above the LTA - sadly, up through most of December, this has not been the case!

Thursday, January 7, 2010

China - the sleeping ice wine giant? (part 2)

And now for the continuation - How China has affected world ice wine production...

Ice wine is deliciously sweet, and due to the many things that have to go right for it to be produced (see part 1) and the low juice yield from the grapes, it is very expensive. So it is very sought after in many places, and also a target for counterfeiters. Some Niagara Peninsula producers were shocked to find that "icewine" was being sold under their brand in China.

There is, apparently, a lot of adulterated table wine being sold as icewine in China, which has a negative impact on the reputation of brands making it the right way, and therefore getting the special characteristics of the wine style that are so yummy.

However, that is not to say that all ice wine being made in China is fake! Changyu winery partnered up with a Canadian company some years ago to develop an expansive vineyard specifically for icewine production. Those Vidal vines are now coming into full production - all 5000 mu (about 333 hectares) of them (there is some confusion over the actual area planted. Some web sources say 5000 acres, but two signs I saw at Changyu say they have 5000 mu (1 mu = 0.067 ha)). The plan is to make icewine under similar conditions as required by the Canadian VQA system, and supply a quality product (Changyu Golden Valley Icewine) to the domestic market.

Changyu Golden Valley Icewine bottles on display at the Yantai International Wine Festival. These are the Golden Diamond wines. There are also two higher price point labels, the Blue Diamond and the Black Diamond ones. Prices for 500ml bottles were 228RMB, 418RMB and 838RMB, respectively. This translated into approximately USD33, 60 and 120, resp.


Some information about the icewine vineyard development. Picture taken in the Changyu Wine Museum, in Yantai, Shandong Province.

The location was chosen so that conditions for quality icewine production would be met most every year, and because the scale is so massive, that means a lot of wine can be produced!

A photo of a photo of the vineyard in Huanren - appropriately icy! Picture taken in the Changyu Wine Museum.

Even considering this is all in China, I still wonder about where they will get all the labour to tend the vines and harvest the fruit!

A photo of a photo of a "Hardworking farmers harvesting grapes in coldness." Picture taken in the Changyu Wine Museum.

And since China does things big, just how significant is this planting in Huanren? In 2008, about 6500 tonnes of grapes were registered for icewine production in the Niagara Peninsula. The Changyu development should produce about 1000 tonnes of grapes (significantly more come from vineyards other than theirs). So a significant boost. Even more significant when the latest info says that only 1750 tonnes were registered to be made into icewine for the 2009 vintage, due to a downturn in the icewine market.

While I'm not a huge fan of the wine style (too sweet for me, generally), it certainly has, and deserves, a place in the market, and is also a good reminder of how versatile a product the grape is!

NB, you might be interested in reading this article, which has more detail on the plantings in Huanren...