You may not realize that wine is most often stabilized and clarified in order to be prepared for its journey from the winery to your glass. I use “often” because winemaking operations that are required to obtain a stable and clear wine are always a contentious topic among producers. There are passionate arguments between winemakers revolving around the potential for removing something good during those operations (stripping aromatics for example) or around the quality of the additives (such as adding animal protein for fining) or around the appropriateness of a given technology (i.e. use of DMDC for microbiological stability). I do not intend to write an opinion piece about all those techniques (perhaps in a follow up blog post), nor do I want to discuss the spectrum of various “umbrella” certifications such as “Natural,” “Biodynamic” and “Organic” though that too would be an interesting topic to discuss as well. Today I want to simply summarize which stability and clarification processes are used, why they are used and what can happen if they are not implemented and you encounter an unstable wine in your wine explorations.
There are five stabilities that a winemaker should consider and a range of clarification techniques based on wine styles. Each one is discussed in the following paragraphs.
Protein stability: Grapes are rich in proteins and are altered during alcoholic fermentation (yeasts take amino acids from the juice and make proteins that get released in the wine when they die). Those proteins have the potential to polymerize, or combine together, to create large insoluble compounds that will appear like a veil or a blob in wine. This only happens in white wines as tannins in red wines naturally fine proteins (which you can witness as your salivary proteins react with red wine tannins drying out your mouth). Because the polymerization of proteins in white wine can be triggered by heat, protein stability is often called “heat stability.” Wineries that desire to avoid this potential risk can do a test in their lab using a fining agent to remove the protein most often Bentonite (a clay that binds proteins and settles by gravity afterwards). Bentonite clay is harmless and actually can be drunk for health benefit. There are a few other techniques to avoid protein instability that involves the introduction of a protecting colloid that stays in the wine such as gum arabic but since Bentonite is inexpensive and totally natural, it is widely used.
Tartaric stability: Grapes are the richest fruit in tartaric acid providing the majority of the acidity in wines. Unfortunately, tartaric acid can bind with potassium and calcium naturally present in wine and create a crystal that settle at the bottom of the bottle (often referred to as “wine diamonds” and commonly mistaken for glass or sugar by consumers). If the crystal is small, it might stay in suspension creating a shimmery haze. This crystallization occurs at cold temperature which is why winemakers refer to tartaric stability as “cold stability.” Wineries that want to avoid this instability can trigger the crystallization in their tanks by chilling the wine close to freezing temperature often adding cream of tartar to provide a “seeding” crystal that grows from there. Another technique is to use an electrodialysis machine that removes calcium and potassium from of the wine with the help of ion selective membranes and a low voltage electrical current. Protecting colloids can also be added such as CarboxyMethylCellulose that will stay in the wine.
Preservation against oxygen: Wine is sensitive to oxygen as many compounds are transformed in its presence. Oxidized wine can smell of bruised apple or worse: vinegar. This is a very technical part of winemaking that requires the winemaker to understand the capacity of the wine to absorb oxygen (red can absorb more oxygen than whites for example). Careful management of oxygen during winemaking, aging and bottling, the choice of closure and the level of antioxidant added (Sulfites being the most used, sometime ascorbic acid) are the tools the producer uses. A small level of sulfite is sufficient to avoid oxidation in an air tight container (glass bottle with screwcap for example) while larger amounts of sulfites are necessary in a permeable container (a bag in the box for example).
Microbiological stability is of prime importance to avoid spoilage. Fortunately, wine has a decent content of alcohol protecting it against most spoilage organisms – only a few bacteria and yeasts are of concern. Wines with residual sugar and/or residual malic acid are the most at risk of spoilage so to combat the risk, they are systematically sterile filtered and have some level of sulfites (sulfites have antibacterial and fungistatic properties on the top of their antioxidant qualities – the swiss army knife of winemaking). The few other microbes that can grow in wine are acetobacter (transforms wine into vinegar) and Brettanomyces (gives wine a strong barnyard, smoky, band aid smell). Interestingly enough a small level of those aromatics (vinegar and barnyard) can be complex and interesting – too much can be a turn off. Means to manage microbiological spoilage include hygiene levels, sulfites use, oxygen management (most of those microbes need oxygen to grow), filtration (down to sterile filtration at bottling), use of sorbate, use of DMDC or fortification (yes, fortified wines are too alcoholic for spoilage organism to attack them).
Metal stability is not something we worry about too much anymore but this used to be a large issue when wineries had equipment that enriched wines in copper, lead or iron and when vineyard managers use to spray metal based chemicals on clusters close to harvest (copper sprays for example). Wines enriched with metal are not very healthy (heavy metal – no thank you) and secondly those metals can combine and precipitate creating hazes and deposits. Those defect are known as “casse.” Removing sources of metal enrichment has made this stability issue all but disappear.
Clarification is different from stabilization in the way that stabilization addresses the potential for a future deposit or haze in the wine while clarification makes the wine itself clear but does not address future problems. Clarification and stabilization work together and are often combined during the winemaking process. For example, a classic sequence of events for our Sweet Riesling would be: centrifugation post primary fermentation (clarification) followed by the addition of sulfites (oxidation and microbiological stability), followed by Bentonite (protein stability), followed by racking of bentonite lees (clarification) following by Electrodialysis (tartaric stability), followed by sterile filtration (clarification). Clarification operations can be separated by “forced clarification” (centrifuge, all types of filtrations) versus racking after settling by gravity.
One last note about particles that get into the bottle at bottling such as bugs, hair, pieces of glass, cardboard fiber and once in a while a piece of the bottling line (We have a bottle at the winery with a bolt in it!). Despite the best efforts of the bottler, sometimes one of those non wine particles gets into the bottle. Causes include the sterility of the bottling room, the rinsing or blowing of each bottle prior filling and the use of proper food packing uniforms (hair nets for example).
So remember the difference between clarification and the five stabilities of which heat, cold and microbiological stabilities are the most important. Next time you see a deposit in a bottle you can think about why it has happened and relate it to a specific winemaking decision.