“Pre-Bottling Adjustments - Racking / Microfiltration”

W.C. PAETZ - January 28, 2004 Michigan State University

Abstract:

During our lab exercise we tasted the wines that we had measured last week to discern what additions or amelioration might be required to enhance their organoleptic properties. An examination of our results from last week was used as a basis for understanding the flavor components and wine stability. As we approached the lab our intention was to rack the wines to remove sediment. Decisions were made regarding amenable factors, which required action. Each wine has certain features which foster conclusions regarding whether or not a certain wine style is suitable and possible or not.

INTRODUCTION:

Bottling is the culmination of years of viticulture and enology activity. Several important issues must be considered prior to this final act. The final presentation of the wine may include a program of bottle aging, however the ability to correct or enhance a wine, is for all intense and purposes terminated when the wine is bottled. Clarity, filtration, fining, stabilization, aging and possible blending of the wine all must be considered prior to bottling. These post fermentation decisions are crucial to the success of the wine maker and must never be left up to chance.

In an article by Andrew Wood, from Divine Magazine(1.) The story was told of a vintage of a particular wine, McGuigan Genus 4 Old Vine Hunter Valley Shiraz. This wine had been judged in several blind tastings in Melbourne, Sydney and Canberra as one of the top wines in the competitions. As a result of these evaluations the magazine published a strong recommendation. Many of their readers rushed out to purchase cases of this special wine as soon as it was released commercially. Many consumers and judges complained when the wine did not begin to live up to the reputation the magazine and judges had conferred upon it. When the wine maker was confronted, He offered several explanations including barrel samples are not really the same and that is what had been judged, he went on to say that the earlier wine did not suffer from bottle shock and that given time the wine would live up to all of the accolades it had received. Eager to address the concerns of all, the magazine directed an analysis of the wines. They actually had some of the original bottles that had been submitted for the contest and purchased others for comparison. Ultimately they concluded that there was a difference in the constituents in the wine. The wine maker admitted that due to marketing pressure they had released the wine too early. Because of the differences in color and palate weight the bottles were analyzed. The tests found significant differences between them. The first bottling contained over 2 g/l of residual sugar, while the second bottling had virtually no residual sugar. The first bottling was ½ percent higher in alcohol than the second. In other words the first wine was stronger and slightly sweeter, the wine commercially available carries the gold medal stickers from the wine shows. Eventually the wine maker said the wine had been bottled at different times from two different batches. Although he argued that the wine’s properties were almost identical, except for slight differences in sugar and alcohol, he will be hard pressed to convince the buying public again to try his award wining wines. Industry authorities did not find him culpable, with out sounding cynical, I would suggest that the Michigan Grape and Wine Counsel would not be so likely to protect one of their own from this type of error. The real lesson here is for one to understand the importance of integrity in wine making. Most enologists go to tremendous effort to produce consistent results.

So what are the compelling elements of wine making that dictate how a wine can be perfected. Included are several post fermentation activities that assure that a wine’s character can be guaranteed year after year. Included are elements such as pH.

According to Eutech Instruments, (2.) “pH is a fundamental element of the wine making industry. PH strongly influences wine properties such as color, oxidation, biological and chemical stability.”
Lower pH values are known to improve the stability of wine, so wine makers prefer a pH range of 3.0 to 3.5. There are many advantages to low pH values in wine. Low pH inhibits bacteria, causes sugar fermentation to progress more evenly and makes malolactic fermentation easier to control. Low pH also has a direct influence on the hot stability of wine. Low pH results in better visual qualities for both red wine and white wine color intensity. When wine pH has high values, bacteria grow rapidly and undesirable bacterial fermentation is more problematic.

Clarity is a desirable factor for all wines. A brilliant crystal clear polished wine is sought after by all wine makers. According to Lum Eisenman, (3.) “Practically all white and blush wines require special clarification treatments. These wines need fining and tight filtration before they attain adequate clarity.”
Racking a wine is the process of removing the wine from container and leaving the sediment behind. This simple operation is repeated several times by most wine makers on wines to promote the gradual clarity without the use of harsh fining materials that might strip out color or flavor from the wine.
Stability issues encompass several factors. These can all be measured and must be known to be able to factually comment on the suitability of a wine for bottling. The status of measures such as pH , free SO2, residual sugar, acid level all contribute to a wines stability and predictable longevity.

Materials and Methods

Titratable Acidity Reduction:
Equipment:
1.) Chart from last weeks experiments
2.) Yardstick to measure volume
3.) Wine thief
4.) Tasting glasses
5.) Scale
6.) Calcium Carbonate
7.) Plastic tray to weigh material
8.) Mixing devise on drill bit

Method:
1.) Measure volume of wine in each carboy
2.) Sample extraction wine thief
3.) Tasting to confirm acidity
4.) Calculate amount of Calcium Carbonate to reduce acid.
5.) Measure and scale C.C.
6.) Place in carboy
7.) Mix

Results
(Figure 1)
L Addition of
Cultivar Vol pH TA Cal. Car.

Carbonic Maceration Foch 96 2.95 9.6 128
Carbonic Maceration Foch 51 2.95 9.6 68
Delaware *A 3.02 7.6 *A
N.W. Vignoles 3.36 12.4 na
Sparkling Foch 56 2.91 12.4 na
Late Harvest Vignoles 102 3.12 14.9 137

Discussion
The ability to follow a consistent program and to keep accurate records regarding what has been done and when it was completed with respect to every wine you make will give you a library to follow regarding the steps for wine making.

There are certain prescribed protocol elements that will direct a wine maker. At all times an up to date document should be maintained regarding every wine being made. It must include cultivar, dates, operations, ingredients, temperature, brix readings, alcohol volume, T A, pH, free SO2.
In addition to racking and fining the process of cold stabilization to remove tartrate crystals may be completed prior to bottling especially in whites. The use of pasteurization or high temperature for a very short time will protect a wine and provide microbial-stability.
Compositional adjustment of acidity, sugar level, ethanol level, tannin removal and sulfide/ mercaptan removal are other adjustments which should be considered.
There are an infinite plethora of considerations regarding the Vinification of an exceptional wine.

Conclusion
This study was not only worth while but extremely important. The capacity to evaluate a wine with analytical tools revealing factual data can lead you to make technologically accurate wines. The capacity to taste a wine and be able to discern taste component dimensions requires much more experience. The only valid rational conclusion is that wine making is as much art as science.

Appendix

Refer to figure 1 in text.

References:

1.) A. Wood, Divine Magazine, Numbers 30 and 31. May 2003
2.) Measuring pH in Wine-Making :www.eutechinst.com/techtips/tech-tips42.htm
3.) L.Eisenman, Home Wine Makers Manual, Chapter 17
Http://home.att.net/~lumeisenman/chapt17.html

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