Cellar sanitation is one of the less glamorous aspects of wine production. It's also one of the most important. The cellar should always be in a ready-to-use state. This allows you to react to production issues without having to factor in cleaning and organizing time. Therefore sanitation is something that should be performed as a maintenance issue, before it becomes something to address in order to process wine.
"Sanitation" has become a catch-all term for routine cleaning operations in the cellar. However, it more properly refers to the removal or inactivation of infectious agents that (in a winery setting) cause spoilage - yeast and bacteria. Most of what we actually do in the cellar as routine maintenance are cleaning operations. This is the removal of the wine, residues, and films that foster the growth of yeast and bacteria. Rinsing surfaces, scrubbing dried grape skins and pulp, and removing the residue of evaporated wine are cleaning operations. If all you've done is make the surface pretty, you've cleaned it well, but you haven't necessarily sanitized it.
Cleaning and sanitizing do follow common sense intuitions. A sanitizing agent won't be very effective if it doesn't come into contact with a surface, so it makes sense to physically clean a surface before attempting to sanitize it. If looks and smells clean, then you've probably cleaned it well enough to prepare it for a sanitizing agent. With simple wine movements cleaning may involve nothing more than rinsing the surface with hot water. During harvest time when we're working with skins and pulp, this will likely involve scrubbing the surface with a brush or scrubbing pad. For large surfaces or difficult to reach areas like the inside of a barrel, pressure washing with water is one method to physically remove surface residues without having to scrub by hand.
Once the surface is clean, it's a judgement call whether to apply a sanitizing agent. Since wine doesn't harbor pathogens (infectious agents that cause disease) wineries don't require as stringent sanitizing protocols as other food processing facilities. If the surface has only come into contact with clean wine sanitizing steps are often omitted altogether. This is common with barrel processing where rinsing with water is all the cleaning a barrel may ever get. A bottling tank that receives sterile filtered wine is a low-risk surface for eliminating the sanitizing agent. High-risk surfaces are barrels that contain wine with elevated VA, red wine fermentation tanks, and wine hoses (especially if you band the fittings on yourself).
So, what are the options for a winery cleaning program? Most small wineries use caustic chemicals. These include soda ash, sodium percarbonate (also a chemical oxidizer), caustic soda (sodium hydroxide), and trisodium phosphate. Their caustic nature is due to their high pH in aqueous solution. The high pH nature of caustics acts as a detergent to physically remove the residue that harbors yeast and bacteria. Caustic chemicals are notoriously difficult to rinse from surfaces, so neutralizing it with a weak acid is required. A common cleaning procedure for not-too-dirty winery equipment is rinsing with water followed by contact (e.g. circulating in place) with a caustic agent, then a water rinse, then neutralizing the residual caustic with a citric acid solution, followed by a final water rinse. I like to include potassium metabisulfite in the citric water solution as a sanitizing agent. I may or may not rinse with water afterward, depending on the circumstances. Hand scrubbing is often involved at the point when using the caustic.
Routine cleaning doesn't normally require a sanitizing step afterward. You may decide with a high risk surface that sanitizing is required either with every cleaning step (e.g. barrel maintenance) or periodically (e.g. wine hoses). Sanitizing agents work differently than cleaning agents. These act as poisons that interfere with some physiological function of an organism. They are used in relatively low (compared to caustics) concentrations and require stringent protocols for preparation, use, and worker protection. Chlorine is by far the world's most popular chemical sanitizing agent in food processing facilities. It's cheap and very effective. Small wineries have largely gotten away from chlorine however due to its role in 2,4,6-trichloroanisole (TCA), one of two chemicals responsible for cork taint. A popular and effective chemical sanitizing agent for small wineries is peracetic acid. It's not poisonous in the way other chemical sanitizers are, though it will damage tissue at the point of contact. Despite its name it's really only a strong oxidizer - it will blister your skin if you touch it, though it probably won't send you to the hospital. Oxidizers physically deform an organism's cell membrane resulting in cell death. Oxidizing agents break down to harmless oxygen and water, unlike poisonous sanitizing agents that remain poisonous after use. In fact, you can actually avoid rinsing peracetic acid altogether after use.
Sulfur dioxide in the form of potassium metabisulfite is a sanitizing agent that is relatively safe to work with, effective, and something you already use in your winery. It's also easy to incorporate in the citric acid rinse in your cleaning program. One of the safest and most effective sanitizing agents in the world is steam. It's byproduct is water and it has the advantage of getting into places liquid sanitizing agents may have difficulty reaching (think of all the connections, twists, and turns in a bottling line). Steam is particularly suited to barrel work as the interior surface is difficult for liquid sanitizing agents to penetrate. Since steam generates heat (condensing water from steam releases a lot of energy) another advantage in barrel use is the vacuum generated by cooling condensation from steam. This extracts wine and sediment from the staves and is pulled into the condensation water where it is simply dumped out after the procedure.
Here are some photos of common sanitation issues in a winery and how I addressed them.