Nutritional Nitrogen Concerns

Nutritional Nitrogen levels in must are season and vineyard dependent. The level that is necessary for a good dependable fermentation (free of hydrogen sulfides or worse) is extremely yeast-dependent (and possibly author-dependent, as well). Depending upon the yeast, an acceptable nitrogen level lies somewhere between 250 and 450 (or more) mg/L of yeast-available-nitrogen (YAN).

The Formol titration in my WineDoc Lab Manual is a simplification of the procedure given in Bruce Zoecklein’s (et al) book, Wine Analysis and Production. Ammonium has been seen to be a fairly consistent 36% of the total YAN, but some variations do occur.

A Lallemand product, GO-Ferm, is designed to provide the start-up yeast cells with everything needed for the first third of the fermentation. It is to be added to the start-up bucket at 110oF, and then have the yeast added at 104oF. Not knowing the YAN numbers, you can safely add 2 pounds of DAP per thousand gallons, and 2 pounds of a supplement like Fermaid K. This particular combination will boost the YAN by 75 mg/L. The DAP and the Fermaid K should be added at about 16 to 15oBrix.

M-L additions: What and When?

The ‘What’ is easy. Use one of the direct addition types: MBR 31, 41, etc. If yeast contact is going to be minimal, or nutrient availability questionable, consider one of the M-L nutrients, such as “Opti ‘Malo” (a difficult pun).

‘When’ is also easy if you have chosen to use a yeast with M-L compatibility, as in low nitrogen requirements, and an M-L bacteria recommended for inoculation early in the fermentation. Dr. Sibylle Krieger-Weber of Lallemand convinced me that M-L inoculation early in the alcohol fermentation is good: either at the onset of alcoholic fermentation, or by 15oBrix. Sticking is not likely to occur if you use a yeast which has low N needs.

Let me know if you have questions in this area.

An important stylistic consideration is whether to maximize or minimize the buttery or diacetyl flavors. To maximize butteriness, hit the wine with SO2 as soon as the M-L fermentation is over. Conversely, to minimize the butteriness, wait until the yeast can metabolize the diacetyl away. Then hit the wine with SO2. This should be a relatively short period of risky exposure with low SO2 in the wine. To keep abreast of the flavor changes requires on-going awareness of the wine’s progress.

To help focus on that awareness, make a sign and put it on your door, or wall by the door: “Taste your wines Frequently!”

Latest research shows that “Co-inoculation” of white wines, a new idea, produces much higher floral character and fruitiness. This information comes from Dr. Sibylle Krieger-Weber also.

Brettanomyces

I supply this info since “Brett” has killed too many “Coulda been good” wines, and not just in Kentucky or the East!

Notes from a talk by Marty Bannister of Vinquiry Barrel Day, 3/16/00, at Wineries Unlimited Lancaster, PA

First identified circa 1900, there are a couple of species, and, now, some different strains. Brett is found in ciders and beers, worldwide.

The microbe can be found in orchards and vineyards, as well as wineries. It is found in all-new wineries, ergo; it came in with the fruit. It thrives in wineries: juice and air moisture are helpful to it.

Aromatic development follows this path:

Loss of fruitiness or varietal character follows a nasty path:

  • Plastic
  • Spicy
  • Leathery
  • Raw meat
  • Animal aromas
  • Fecal stuff

The plastic phase has been characterized as Band-Aid aromas.

The compounds involved in the aromas have been identified as 4-ethyl phenol and 4-ethyl quaiacol, in a ratio of about four to one of the phenol to quaiacol.

Threshold for aroma detection is about 400 ppb; it is ugly at 2000 ppb.

Aroma detection is very close to maximum preference.

100 ppb (0.1 ppm) separates the detection threshold from the defect threshold.

IT IS UNPREDICTABLE.

Brett growth activity does not often occur during primary yeast fermentation. Watch stuck wines carefully, since Brett grows well on low levels of residual sugar.

Dry wine may be defined as having less than 0.1% RS, BUT Brett can still grow at levels down to 0.02% RS.

Faster growth occurs at higher temperatures, and in the presence of Oxygen.

IN BARRELS:

Brett grows much more rapidly in barrels because Brett can eat the disaccharides formed in toasting the wood, and by splitting sugars off polyphenols. Red wines are the most common host.

CONTROL IS BY SO2. 0.8 ppm molecular SO2 kills Brett, and 0.5 to 0.6 seems to control it. When racking, leave bottoms if there is any reason to believe that Brett is around.

Growth habit:

Anaerobic > 4-ethyl phenol

Aerobic > acetic acid

It is important to re-adjust SO2 levels upwards. Use “the Cottrell Rule”.

SENSORY:

It is too late when you can smell it.

4-ethyl phenol can be measured, and that is a way to track Brett growth, BUT culturing should be done, too. In culturing with actidione, Brett forms moth-ball-like domes. Microscope searches can’t pick up Brett until the population is much too large. The typical look is ogive shape with bud scars.

Timing of sampling for Brett: mixing the barrel is best since Brett cells tend to drop to the bottom, otherwise take sample from as deep in the barrel as possible.

IN BOTTLES:

The bad aromas will intensify if live Brett cells are there!

OTHER CONTROLS:

DMDC/Velcorin controls Brett both in bottling and in barrels, but is generally too expensive and too hazardous for small wineries.

Barrel Sanitizing:

Clean it

Peroxycarb (Barrel Builders sells it.)

Ozone – as effective as Peroxycarb.

DRY STORAGE is good.

Crosby & Baker (MA) sell a Di-oxygen sterilant which also works well in Barrels (updated in 2002)

Note: Barrels cannot be sterilized. Barrels which give rise to Brett should be recycled (destroyed for wine use: made into planters, short skis, etc.

Mix it Up! Reduce bottle to bottle variations

Recently I have been surprised by some wild bottle-to-bottle variations.

I remembered an incident in the early nineties when a Nouveau wine bottled on November 13th had gradually increasing sugar from case 1 to case (about) 800.

My trusted and quite good lead cellarman assured me that he had thoroughly mixed the tank after sweetening. We guessed that the sugar had sunk, and never got distributed. Happily, the wine sold so fast that no one ever got a second case, and so, never came across the sugar differences.

Last year a local winery had the same inadequate distribution, but the addition was SO2. The last third of the cased wine will keep for 30 years easily! Consumers attempting to consume wine in that portion were not pleased.

A third incident with another nearby winery has prompted me to put this out for you to consider. Use of ‘Method A’ would avoid theses surprises. Racking close to bottling would also mix the batch well. Please do one or the other.

While it might sound boring for all the bottles in a release to be the same, customers do appreciate it.

Good mixing,

Tom