By: Thomas J. Payette, Winemaking Consultant
Fining trials on white, blushes and some rose wines can be critical to determine the least amount of bentonite needed to achieve heat stability or protein stability. Other fruit wines may need fining also.
The most difficult part of fining trials is to have an understanding of working with such small volumes of wines in the lab and how to apply the trial calculations to the larger tanks. Once one has a clear understanding and methodology the tasks become easier. It may take several fining trials under ones belt before it becomes second nature and the task becomes “a piece of cake.” It is recommended an outside lab be used to mirror your winery lab until such point the internal winery lab technician feels comfortable doing the test on his or her own.
It is important to do bentonite fining trials on even perfectly clear wine. These perhaps perfectly clear wines may contain proteins that, when becoming warm or hot, may denature and form a haze, cloudiness or even sediment in your bottled wine. Although your winery is generally very cool you must anticipate “outside abuse” of your product and protect it because anything wrong in a bottle with your label on it – reflects poorly on your winery.
Below is a list of equipment and instructions to perform your own trials in your winery lab.
Most winery labs have the basics and one should be able to acquire these additional items with little financial outlay. Here is a list of basics.
1. Bentonite from your cellar bulk fining agents.
2. 375 milliliter screw cap wine bottles (splits) – may reuse these.
3. 500 ml beakers
4. 500 ml Erlenmeyer flasks
5. Millipore filter apparatus plus ample 0.45 micron filters.
6. 545 DE as a filter aid, if needed
7. Vacuum source for filter
8. 20 x 150 mm test tubes with screw caps
9. Test tube rack holder or coffee cup
10. Stir plate with magnetic stir bars
11. Good scales to weight fining agent / bentonite
12. Good eyesight or a Nephelometer (optional)
13. Distilled water or tap water (non-chlorinated) for mixing bentonite.
14. Graduated cylinder ( 100 milliliter )
15. Pipettes 1ml, 2ml, 3 ml, 4ml, 5ml. Or serological (preferred).
16. Crock pot cooker or similar
17. Wine glasses – don’t forget the wine glass!
Agents should be made fresh each time a fining trial is to be performed or kept less than a month at room temperature. Always remix the bentonite slurry before using in a trial. Use bentonite directly from the cellar to make sure the trial will match/reflect the desired reaction in the wine tank. If different batches of bentonite are used in the lab and cellar – the results may vary.
1. Select and prepare a 5% bentonite slurry solution by carefully dissolving 5 grams of bentonite in about 80 milliliters of 80 degree F water. After properly mixed bring to volume with water to exactly 100 mils to make the 5% solution. This step may be done in the 100 milliliter graduated cylinder listed above.
2. Collect the proper volume of wine from the wine tank desired to perform the fining trial on. Make sure the sample is representative of the complete wine tank otherwise results will not be reflected properly after the fining has been completed in the wine tank. If planning to do 5 different levels of additions in a trial you may need 3 liters or more of wine. Break down the volume of wine into 6 – 500 ml Erlenmeyer Flasks and have them remain as close to the cellar tank fining temperature as possible.
3. Label the Erlenmeyer flasks at the rates desired to be tested in the lab trial. Typically each wine will have two controls, a one pound per thousand, two pound per thousand gallons and so on up to 5 pounds per 1000 gallons trials. Some varietals may require more bentonite but those will start to identify themselves in your winery and each year you will “know or anticipate” they may require more.
4. Now we know the above mixed solution is a strength that 0.24 mils of a 5.0% solution per hundred milliliters of wine sample will equal a one pound per 1000 gallons addition rate.
Extrapolating that out for example: If one prefers to make a 400 milliliter trial and to settle in a 375 milliliter screw cap bottle one would add 0.96 milliliters of a 5% solution to a 400 milliliter sample to represent 1 pound per thousand gallons; mix and transfer into the 375 milliliter bottle. Further – add 1.92 milliliters of a 5% solution to 400 milliliters of sample to equal 2 pounds per thousands and so on.
Metric: For those that prefer metric the addition can be viewed this way. One pound per thousand gallons equals 454 grams per 3785 liters or 0.048 grams in 400 milliliters. This is the same as the above calculation using 0.96 milliliters of a 5% solution in 400 milliliters.
5. When adding the bentonite slurry to the wine – make sure to be mixing the sample well yet do not use shearing force mixers such as a blender. Use the amount of agitation one can expect to have in the wine tank while adding the fining agents while mixing in the cellar. Always try and mimic the actual cellar experience as closely as possible in the lab. If your lab has a magnetic stir bar assembly these work very well.
6. Continue to mix the samples thoroughly after the addition of the agent or agents. Perhaps a minute or so on a magnetic stir bar mixer.
7. Discontinue mixing and transfer the wine into a labeled 375-ml wine bottle and place the screw cap on top. The label should reflect the addition rate of that sample such a 0, 1,2,3,4,5.
8. Place, in a dark area, in the cellar or lab at or near the exact wine tank temperature if possible.
9. Allow to settle overnight or several days.
10. Decant into a labeled beaker at least 250 mils of the 400-ml samples from each fining trial. One portion, approximately 50 milliliters per person, may be transferred into pre-determined labeled clean wine glass for visual, sensory and palate evaluation. The other portion should move forward for further lab testing for the protein stability examination.
11. The above analysis will allow one to taste different fining agent levels to help understand the rate of bentonite added and the expected sensory changes, if any, found at different levels. Remember to incorporate an unfined sample in your tastings and lab work as a reference point to determine if a fining should be performed, at all, on a certain wine.
12. If the wines are not settled enough for visual examination one can employ the 0.45 micron filter listed above to filter out suspended particles. If sensory is to be done after filtrations make sure to treat the filter pads prior to use with a light citric acid solution. This will remove any filter pad flavor. This same filtered wine can then be moved forward to the protein testing below. Use a new filter pad for each sample to eliminate sloughing of the proteins from one sample to the next.
Simple Protein Test
Using the clean, dry 20×150 mm screw cap test tubes above fill each one about half full with the varying filtered fining trial levels created above. Label each test tube respective to its “pounds per thousands” contents. For each wine have a control sample that will go through the heat treatment described and one that will remain with no heating.
Collect each sample after filtering in the lab in its respective test tube labeled 0,1,2…5.
Heat the test tubes in a crock pot with water to roughly 70 degrees C ( near 160 degrees F) for 8 hours. (See photo bellow) This is a great place to use the test tube holder or coffee cup.
Remove the test tubes from the heat source and allow to cool to room temperature. Visually inspect, under a bright light source, for any sediment or haze that may have formed in the test tubes of wine. Compare to the control sample as well. Re-examine the following day to see if other changes have taken place with a flocculate formation or haze. Most winemakers may use eyesight while others trust the Nephelometer listed above. (I have always just used eyesight)
Determine what fining level gives the wine the desired protein/heat stability.
Once you have determined what amount of bentonite is necessary to make the wine protein/heat stable then perform the fining in the tank at that same rate. For example if you find two pounds per 1000 gallons remained clear in the testing after heating then you have determined that rate should be used in the cellar after proper rehydration of the bentonite. Once the wine is racked off the fining agent and collected in a clean tank you should perform another heat test, without the trials as a pass / fail test only, to determine if the wine performed in the tank as the trial predicted. Always double check the results after performing the fining in the tank.
Other Helpful Tips:
Make sure the wines or juices are low in Carbon Dioxide gas since the bubbles may attach to the bentonite preventing it from settling in the tank or lab beaker.
PH affects the rate of settling – lower pH wines generally settle faster in almost all cases.
The bentonite protein reaction is a positive negative charge reaction – and then settling allows separation from the reacted bentonite.
Most winemakers leave the bentonite in the wine tank to settle roughly 20 days. Anything past 30 days may result in the proteins sloughing off the bentonite since the positive /negative charge may weaken.
The ultimate goal of a fining trial is to use the least amount of fining agent possible to achieve the stability desired for the wine.
Use pipettes to accurately measure the fining agents. Serological pipettes offer nice results with incremental additions. Think of how you can perform fining trials in your lab and set aside future time to work with your plan. You will be amazed at how much refining can be done to wine and how easy it really is. Make this a part of your work improvement schedule for the year to come!
Summary: Recall this is only one task to perform on white / rose wines wines generally prior to bottling. Often three months from bottling is a time to look at the blends to perform finings and other stabilities before bottling. Bentonite finings in the cellar should settle 20 days, roughly, to avoid heavy racking losses. Don’t forget aroma trials also before adding bentonite. Copper additions before adding bentonite may help remove any excess copper after reaction. Cold/tartrate stability actions are typically taken after achieving protein stability. Those wineries still going “unfined and unfiltered” may look at their products with the above tests just to make sure they are comfortable with the possible results.