30 July 2014

Composition of Grape vs Honey Musts, Part 2

This part will deal with yeast assimilable nitrogen. Now, we are all familiar with the concept that mead musts don't have enough yeast assimilable nitrogen (YAN), or at least they tend not to have enough for us to be comfortable with. Here, we will take a look, not only at the total levels of YAN, but which constituent parts are involved in the differences between grape and honey must.

What is going to be our baseline? That is a very interesting question as the specific amino acid profile of a grape must depends on the variety, specific clone, climate, vintage, soil type, and what vineyard practices occur. There are some basic profiles that can be drawn based on grape varietal, and differenced between red and white, so we will look at a few white varieties and the average for them. The same problem exists with honey: the specific amino acids and their ratios are heavily determined by floral source, but the weather will also play a major role (with drier weather usually meaning more pollen content, and thus more amino acids), as will the region (again having to do with nectar sources).

Just look how different they all are. To better illustrate the point, lets look at the profiles of an average white grape must, honey, and pollen.

Notice how honey and pollen have much higher levels of proline compared to the other amino acids, over half, while grape musts have proline representing about one fourth of the amino acids. Keep in mind that yeast can only use minute traces of proline (only when respiration is dominant compared to fermentation, which is incredibly rare in fermenting musts), and while arginine is utilized by yeast, they far prefer glutamic acid and glutamine, which show higher ratios in pollen (and therefore honey), in comparison to grape musts. 

Here we get to see how two different honey musts compare to average white grape must. The honey must with pollen (30g/L) is closer to the levels of wine must, but it still has a ways to go. This represents a mead must made with 3lbs honey per gallon, but changing the concentration of honey to water changes the amino acid levels to a considerable degree. 

The more honey, the more amino acids, but also a higher starting gravity. Increasing pollen additions also help add amino acids, and if your honey is not filtered you may have anywhere from 1g/L to 5g/L, though this still represents only a small increase in YAN (<20ppm), far from what is considered acceptable.

While pollen additions seem very effective, there can be a bitter flavor that accompanies the pollen, especially if it is of low quality (be warned, the majority of freeze dried pollen sold in the US is from china, even if the guy at the farmers market is selling it).

P.S. See . . . I told you more pictures! Also I'll get a half-a$$ bibliography soon; just a busy drone, even if I am male.

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