Must analysis

MSU HRT 434 L: Enology Laboratory September 25, 2003 - W.C. Paetz

Abstract:
Accurate must analysis is critical to making a desirable wine. The need to adjust prior to fermentation is desirable. To discern the status of various elements in our juice several tests were conducted. These included “Clinitest” and hydrometer readings from a sample of Marechal Foch.

The analysis of a recent harvest of Vignoles gave the following readings: pH = 3.05, Brix = 19.6 and TA = 16.43. The decision was made that deacidification was necessary on this must.

Prior to this step it was necessary to conduct the first racking to separate the potential wine from undesirable solid matter that had settled during the initial stage in the primary fermentation vessel.

It was necessary to prepare yeast for starting the fermentation of a Pinot Noir.
Although these various actions do not seem to follow a systematic flow conducted in a series on all wines they are all important and must be understood to know when they are necessary.

Introduction:
The “Clinitest” is used to monitor blood sugar in diabetics, for our purpose it was conducted to discern the residual sugar in must.

The Hydrometer Method is also used to measure Brix or specific gravity and we used it to discern the rate of fermentation of our Marechal Foch.

Racking Vignoles was completed to separate the potential wine from solid matter that had settled during the initial stage in the primary fermenter.

Deacidification of Vignoles juice was completed to reduce the high acid of this juice. The grapes were harvested from our farm in Lansing, Michigan. Many cold climate cultivars experience high acid and low pH as well as low Brix readings in cold climate viticulture.

The last process that was studied was how to prepare a yeast culture for casting into a wine to begin fermentation.

Materials / Methods:
The “Clinitest”required the following equipment and materials.

½ ml of must. (Marechal Foch)
small glass vial
reagent tablets for glucose analysis
Color comparison chart for residual sugar reading.

The reagent tablets were placed in a clean dry vial and the must sample was poured into the vial. There was an exothermic reaction and the sample turned to a green color indicating from the test that there was a .5 g/l of sugar in the sample or .05 Brix.

According to Daniel Pambianchi, “ This test is less accurate for red wines because phenolic compounds, including tannins and color pigments, interfere with the test.” (1.)

The hydrometer reading required the following materials and equipment:
Hydrometer
Testing jar
Sample of Marechal Foch

We made sure the hydrometer was clean and that our must selection was primarily liquid with no stems, seeds or bits of fruit. The testing jar was filled to approximately one inch from the top. The temperature of our hydrometer was calibrated for a correct reading at 20 degrees C. The temperature of our must was at 17 degrees and an adjustment to the reading was necessary. The hydrometer was placed into the jar. It was then grasped by the top and given a gentle spin to remove any air or co2 from the sides of the hydrometer. The reading was taken from the number which was at the bottom of the meniscus. This turned out to be .80 which when calibrated for temperature subtracting .18 our final reading was .62 Brix.

Deacidification of Vignoles.
The following materials were required to prepare for this process.
Calcium Carbonate
Scale to measure with
Plastic tray to measure in.

The formula for reduction of acid is 1 G/L of calcium carbonate = 1 G/L of Acid Reduction. We had a reading in our must of 16.43 TA and desired to reduce it by 3 G/L. To do so we multiplied our total must by the volume of 35 Gallons by 3.785 which converts it to 132.5 liters we require three grams per liter to reduce the acid by the same amount so we multiply this times a factor of three for a result of 397.5 grams for the 35 gallons of wine.

This was our theory but the decision was made to separate the must into two different carbouys. One of four gallons and the balance of 30 gallons in the primary. The four gallon sample was to be completely acid free and then would be poured back into the must. How ever the same formula was followed for each of the volumes of wine. That is the four gallon carbouys were treated with 45 grams of Calcium Carbonate and the remaining 30 gallons of wine was treated with 340 grams of calcium carbonate.

Yeast Starter Preparation required the following materials and processes to inoculate a Pinot Noir must:
Yeast Lavalin D47 6 packets of yeast or 30 Grams
“Go-Ferm” wine yeast nutrient 1.14 x 30 = 34.20 Grams
300 ml of warm water
measuring tray
Warming vat

The “Go-Ferm” and the Yeast were measured and mixed together and placed in the warming vat to allow the yeast to be re-hydrated as well as to begin to reproduce. This was to require an hours time before the yeast would be ready to pour into the Pinot Noir and for the fermentation to begin.

Racking is the removal of the must from solids that have settled in the bottom of the container. The following equipment and process were required.
Impeller Pump
Plastic hoses to transfer the must
CO2 tank
Clean receiving barrel.

The hoses were cleaned and used to transfer the must from one container into another clean container. The self priming pump easily pulled the must from the carbouy and pushed it into the receiving barrel. The must was removed from the donor carbouy, down to the point where there were solids in the bottom of the carbouy. The new carbouy was then topped off with a layer of CO2 from a tank filled by placing the hose in the new carbouy and turning the regulator on.

Results: These processes may be necessary but do not follow a systematic flow so that one might understand how wine is made by following them. We did have objectives and these were completed with each activity.

Clinitest = .05 Brix and .5 G/L sugar

Hydrometer Readings : .62 Brix

Deacidification: 3 G/L

Yeast re-hydration: Fermentation

Racking : Visual and measurable change in volume of must.



Discussion:
All of the processes we followed are relevant to wine making. I am certain that future tests and processes will further help to bring into focus the professional wine making skills we all seek. I am very excited about our gradual approach to the various methodologies it is very easy to get confused and frustrated trying to assimilate so much information.

Other methods for determining residual sugar concentration are available. The Rebelein method is probably one of the most popular and widely used in commercial wine analysis. The more accurate the result the better decisions we can make as wine makers. (2.)

Lowering the acid level. High acid is often a problem with hybrid grapes from northern and eastern parts of the United States. Acidex is the best known commercial product used to reduce acid levels. (3.)

Conclusions: The more I learn the more I understand just how little I actually know.

References:
Wine Maker Magazine April 2002 D. Pambianchi, How Sweet It Is?. Measuring residual sugar content.
1. Wine Making S.F. Anderson Harcourt Brace, 1989
2. Winery Technology and Operations Y. Margalit.

Back to MSU Page for more articles