Educational digressions

More about sugars

As grapes ripen, their level of sugar increases. The level of sugar can be measured with a refractometer, and in Australia is measured in Baume – or Brix. After the grapes have been picked, they can be fermented to make wine. The fermentation process converts the sugar to alcohol. In general, 1 degree of Baume works out to about 1% alcohol –if fully fermented to dryness,

The winemaker may add a commercial yeast, or wait for natural, wild yeast to begin the ferment. These natural yeasts may be ambient yeasts from the winery! There are many different commercial yeasts, which may be selected to ferment “cleanly” and efficiently or may suit particular varieties etc. Some winemakers will conduct trials using different yeasts on batches of grapes to determine which is most appropriate.

Interestingly, efforts are being made to shape yeasts to become less effective at converting sugar to alcohol. Climate change is increasing ripeness of grapes, and techniques such as canopy management and earlier picking are only part of the remedy ….. Another anecdotal cause is a degree of backlash against alcoholic bruisers of wines (say those with more than 14.5%alcohol).

The fermentation process can take days (or weeks) and produces heat (and carbon dioxide).

For grapes that are picked very ripe, – or have botrytis (a mould that increases sugar concentration) the fermentation may stop – or proceed extremely slowly when the yeasts are exhausted, or the sugar levels are too high for yeasts to continue to work, or various other reasons. Winemakers may choose to also stop fermentation by reducing the temperature of the wine, or by adding alcohol (spirit).


In general, red wines are fermented to dryness, but they may still contain a small amount of residual sugar – perhaps 1-2 grams per litre of residual sugar. This is harmless and not detectable by most people. White wines can carry a little more; Sparkling whites a little more (current debates are about the age-worthiness of ‘sauvage” styles); sparkling reds need some sugar to offset the tannins. Then for deliberately sweet wines esp with botrytis, there is no limit (although fermentation may proceed very slowly- sometimes years!). The table below may be of some help. Main issues with botrytis is that other moulds co-exist. The key to all the sweet style is balance; sugar, acid, alcohol

Table of residual sugar (grams per litre)

  • Dry red <2
  • Dry white
  • Off-dry whites (10-20)
  • Sparkling whites (10 is average)
  • Sparkling reds – (10-30)
  • Muscat, Tokay, Tawny port, Vintage Port (100-200,or more!)
  • Sweet whites >60; can get to 350 in extreme cases; sauternes sit in the 100-160 range

Meeting Brett again

Brett (brettanomyces), ruined 4 wines at a dinner recently.

Brett is mainly seen in red wines, generally in Cabernet-dominant or Rhone varietals wines. It’s less frequently found in Pinot Noir. Brett seems more prevalent in (older), European wines, which is a tribute to cleaner, modern winemaking.

Technically, brett is singly- or in combination -4EP (4-ethyl phenol), 4EG (4-ethylguaiacol) and isovaleric acid (which smells like extreme parmesan cheese, towards vomit!)

Few critics and commentators mention brett in their tastings, despite its occurrence. People have different thresholds for detecting brett, and different evaluations, but its often the elephant in the room. It’s a wine fault.

Some defend the presence of “good” brett, arguing that it can add complexity. I view brett as a veil, hiding the fruit, and ultimately reducing the individuality of wines. If all wines had brett, they would be more similar…

So how can I detect brett? Its not so easy, especially when tasting “savoury” styled wines.

There can be sensations like

  • Horsey, barnyard
  • Bandaid, antiseptic
  • Ozone, seaspray
  • Hard dry finish and metallic notes
  • Bacon, smoke/spice

But the crunch is, has the fruit been flattened or dulled? Brett symptoms are like TCA (cork taint) without some of the strongly negative cardboard aspects.

The level of brett varies from bottle to bottle, so from any batch of the same wine, there will be variation. If you enjoy cellaring wines, you will see more brett (alas), partly as the brett molecules multiply over time, and partly as the natural development of secondary and tertiary characters will reduce primary (fruity) characters. The brett characters will seem more obvious.

Be aware that if you detect brett, you will be described as being a member of the Brett police, or a brett nazi, and be seen as a party-pooper ruining the enjoyment of (especially) older, expensive European wines.

Winemakers have some ways to eliminate brett– or at least reduce its incidence –all hygiene -related!

  • barrel age – not too old
  • attention to sulphur levels (not too low)
  • Attention to pH (not too high)
  • Sterile filtration
  • Discarding affected barrels

The move to “natural” wines is likely to increase the proportion of faulty wines.

Do you prefer the traditional style, or the modern style? The former has Brett, the latter is severely ripe and over-oaked.


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