Cross-Contamination and the Winery Cellar

By: Thomas J. Payette, Winemaking Consultant

Cross-contamination is something we have all been made aware because of the food industry.  We have learned that using the same plate to take food to the grill as well as to serve food from the grill, prior to proper cleaning, may result in a salmonella outbreak causing discomfort to many.  Using a cutting board to prepare a meat or fish and then to cut a vegetable for a salad may result in similar reactions due to a bacterial contamination from an uncooked meat source to a product eaten raw.  Once one focuses on these same principals and perhaps has training in microbiology one keenly becomes aware of the principals of cross-contamination.

  An everyday less seen example outside the food industry is easy to illustrate.  After using the rest room we wash our hands diligently only to turn around and place our hand on the door handle to exit the rest room.  At that instant we have contaminated our hand with microorganisms from other individuals that have placed their hands on the same door handle prior to us.  Perhaps we have all seen the individual that continues to use the paper towel to maneuver the door handle and then throwing away the paper towel.  This is a microorganism conscientious individual that understands the above principal.  COVID 19 also has us all more aware these days to microbes in general.

  Looking at our own cellars, we may find many areas that need work to prevent microbiological cross-contamination.  This article will explore some areas that are culprits in the spread of microorganisms.  Every winemaker needs to have great hygiene and sanitation in the cellar to have the control a winemaker needs to make sound wines.  After reading this article, the cellar will become a different place as other sources of contamination become evident to the cellar team.

  SAMPLING: Most wineries, with sound wines, may taste from vessel to vessel while returning the leftover portion back to the vessel sampled with no worries.  This is one of the major areas that may need tightening up if the winery is experiencing problems.  Winemakers sample from one vessel to another perhaps expressing discontent in one form or another.  Often the discontent is directly linked to a spoilage bacteria or yeast that is growing “unchecked”.  The novice winemaker may rapidly move through the cellar’s containers in hopes of quickly reaching a vessel that has not progressed negatively.  What some winemakers don’t catch on to is that they are indeed the culprits to the spread of the very element with which they are not happy.  When sampling a container, look inside the vessel for a potential surface film. This may indicate a spoilage position for that wine.  Know the sulfur dioxide and ph of the wine.  When experiencing spoilage yeast or bacteria, be sure to sanitize/sterilize the sampling instrument and wine glass between samples.  Do not return the leftover portion to the vessel and be careful to discard the leftover in an area to be cleaned.  Do not dump it in the drain or on the floor for reasons to be explained later. (In clean cellars where sound wines are made it is not usually a problem to sample and pour back wines – only in unsound conditions should one avoid this habit.)

  TRANSFERS: If working with wines that are known to have some risk of infection – always move them last in the day of the transfers. Clean the hoses, pumps and other areas of wine contact between movements.  An example: If 40 barrels need to be racked and one barrel may be suspect to have some spoilage, rack the 39 barrels first then rack the last barrel separate to another tank – do not mix it into the blend.  If the wine is to be returned to barrel give serious consideration to returning the suspect wine to the same barrel from which it was removed to “contain” the spoilage and create a quarantine type situation.  Once the movements of any suspect wines have been made, thoroughly clean the pumps and hoses before resuming to the next transfer.  Be sure to clean the racking wand or any other devices that have had contact with the suspect wine.  Mark the exterior of these suspect vessels so others will be aware of the problem and cross-contamination will be minimized during sampling.

  TOPPING: Another area of great concern for cross contamination is topping.  Make sure to top wines with only clean sound wines of the same type or variety.  Often the topping wine of choice may be a recently sterile filtered dry wine that the winemaker has prepared for bottling.  This wine should have a greatly reduced yeast and bacterial load.  Always use clean wines for topping because the risk of spreading organisms is great here.

  BLENDING: If potential spoilage wines have been caught early, quarantined, and arrested they may still be used in a final blend in small quantities.  If the wines have been cared for and kept “in check” they may add to the complexity of the wine.  This should always be determined by a lab blending trial first.  The trick with blending is to wait to the last possible moment to make the blend to achieve protein, color and tartrate stability of the wine prior to bottling.  This should be done in stainless steel because it is easier to clean and sanitize after removing the wine from the vessel.  After blending, the wine should be filtered as soon as possible to eliminate the bacterial load.

  HANDS & CLOTHING: As with many processing and preparation cellars, always wash your hands frequently especially after handling wines that are suspect.  Be certain not to wipe your hands on your clothing, prior to washing them, after handling suspect wines.  This is the main reason that early in this article it is recommended to move suspect wines last in the day.  Always wear clean clothing from day to day.  Think in terms of what to do when.  If starting a yeast culture for sparkling wine production and bottling a sweet wine all in the same day, use common sense to work with the bottling first and then to work with the yeast starter culture.  Otherwise a major cross-contamination could occur resulting in a re-fermentation of the bottled wines.

  INSECTS & CREATURES: Insects and other mobile creatures are a large source of contamination that is more difficult to control.  For this reason a strong sanitation program is always recommended.  Fruit flies and other flying insects are always a difficult battle during crush and throughout the year.  Incorporate the elimination of these creatures, as best as possible, as a major part the sanitation program.  These insects fly from the drains to open vessels and handling tools such as: hoses, fittings, buckets, racking wands, pumps, filler spouts and many other areas.  Every surface they land on will have a cross-contamination residue left on it from their previous landings!  This was the reason under “sampling” it is recommended best not to pour samples known to contain spoilage yeast or bacteria on the floor.  These areas may become a food source for the insect or simply may be an area of contact for an insect or other creature.

  CHEMICALS & DRY GOODS: Chemicals and other dry goods are often an overlooked source of potential problems.  Using scoops for one material and then using them for another before cleansing will result in a cross contamination.  Soiled scoops will always transfer one material to the other as they are used.  Open containers of chemicals such as acids, bentonite and sugar bags must be avoided.  Cross-contamination is not always microbiological!  A classic example of this is one who uses a soiled scoop from citric acid and then places that same scoop into a container of metabi-sulfite.  This will result in a huge and persistent sulfur dioxide aroma cloud near the incident.  Seal all bags / containers after using them because contamination from insects and other potential rodents may result in problems.  If not already a standard procedure, reseal all open cork bags and other dry goods materials immediately after opening and partial use. 

  AIRLOCKS & BUNGS: Airlocks and bungs need to be thoroughly cleaned after each use.  Airlocks are exposed to moisture and liquids.  This moisture will support bacterial and yeast growth, which must be eliminated before placing them on another vessel.  Since containers may pull a vacuum during a cool down in the cellar after fermentation and draw some of the water into the container.  Clean them thoroughly before storage and before use.  When storing airlocks be sure to blow out any water and allow them to air dry.  Bungs are similar.  When working with barrels remove the bungs and clean them with a cleaning solution.  Rinse them in a low ph water solution to rinse and neutralize the cleaning solution and then replace them on the vessel.  If possible it is best to have a large number of extra clean bungs available to use with the current day’s barrel work.  If so – one can collect the bungs off the barrels for that day’s work and soak them in the cleaning solution.  Clean and rinse them at your leisure after the day’s work.  Allow them to dry and they will be ready for the next day of barrel work.

  POMACE: Remove all pomace from the winery as soon as possible.  It is a food source for yeast and spoilage bacteria.  Try to take the pomace as far from the winery as possible and consider treating it with copious amounts of hydrated lime to elevate the ph and to keep odors in check.  This elevation in ph will prevent lower ph bacteria from growing and result in safer pomace as far as cross-contamination is concerned.  Birds, insects and animals may visit this pomace pile before traveling to other areas, perhaps near or in your winery, carrying spoilage microbes with them. 

  FILTER PADS & DE: Removing filter pads from a filter and placing them in an indoor trash receptacle that is emptied only once a week has never made microbiological sense.  Instead remove them as rapidly as possible from the cellar and get them to a trash receptacle outside and off the property to avoid spoilage yeast from growing and being transferred to other areas in or near your winery.  Not only are they growing unwanted microbes – but also left long enough they will become very pungent!  Diatomaceous earth should be treated the same way or disposed of properly for bacteria growth reasons.

  TANKS: Clean the wine tanks just after emptying.  Once emptied the vessel will be open for insects to fly and move about freely inside the vessel so it should be cleaned.  If residuals of wine are left in the tank they will spoil and become cross-contamination sources.

  SUMMARY: The above examples are just some areas to consider.  Each winery cellar is different and each cellar has unique areas that need attention with regards to the above practices.  Take some time to walk around the cellar and out on the crush pad to explore possible areas to tighten up the sanitation regime to minimize and eliminate cross-contamination sources from the cellar.

  It should be the desire of every winemaker to have and keep a spoilage bacteria-free cellar.  Wines are easy to make and to keep in a healthy condition.  If the wines are kept free of spoilage conditions the workload is less.  Once spoilage conditions exist, the winemaker’s efforts are complicated and more time and effort is needed to focus on extreme sanitation measures.  Every winemaker should employ good winemaking practices to avoid such situations, which are easily avoided with proper cellar management.

  Cross contamination is the number one reason for wine spoilage, as the microbe has to come into your winery from one source or another to begin to grow.

  You will find your winery a different place after you review your cellar and identify sources of cross-contamination.  The wines will improve as a result of your diligence to remove cross-contamination sources, once identified.

Bon Chance!

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