Goodness, you’ve got a persistent sediment source in your wines that’s for sure. You’ve removed the gross particles by racking and filtration.You’ve cleared out proteins by using bentonite. You’ve taken out excess tannins with proteins like egg whites and isinglass. Also you’ve provided plenty of time for settling before bottling and have sterile-filtered right before bottling, excluding any spoilage microbes which might start some kind of post-bottling fermentation and sedimentation. What this tells me is that the source of your sediment(s) is/are smaller than the 0.45-micron size of a bacteria cell, and that it’s something happening on the molecular level in your wine.
Let me run through some things that might help, depending on what is causing your post-bottling instability:
-Don’t make any last-minute blends: I’m guessing your sediment is coming from unstable color compounds, potassium bitartrate crystals, or a mix of the two. Both are small enough to pass through a sterile filter and affect your wine down the road. Are you making blends right before bottling? Even if you have two different batches of racked, fined, and filtered wine, if you mix them together right before bottling their components could create an unstable wine which could throw a sediment in the bottle later. By getting the blend together as early as is practical, you allow time for those reactions to occur and you’ve got plenty of time to correct for, and rack the wine off, any instabilities. Last-minute blends risks unforeseen consequences, one of which can certainly be unstable pigments and potassium tartrate instabilities.
-Don’t make any last-minute macro-chemistry changes: Like last-minute blending, making any big swings like acid-adjustment or blending a low-alcohol with a high-alcohol wine are both a recipe for instabilities. Be sure you’re doing most of your big adjustments and changes months before bottling.
-Chill to force tartrate stabilization: While red wines aren’t normally cold stabilized (chilled to 35 °F/2 °C for a few weeks and seeded with potassium bitartrate crystals, then racked off the sediment), excess potassium bitartrate in your wine can still cause a big mess in the bottle. By putting your wine through a cold-storage regimen, it’s possible that the formation of crystals would be forced, resulting in fewer crystals and less sediment down the road. Do you have a wine or beer fridge? Can you store your carboys outside during the winter for few weeks? I’ll bet in Michigan you probably have a garden shed, garage overhang, or space under your porch where you could store your carboys for a few weeks, if there were a period in the fall, winter, or spring where the temperatures fluctuated between 35–45 °F (2–7 °C). You don’t want it so cold that your wine will freeze and burst the carboys, and you don’t want it to be warm, so your wine is cooking out of doors. A fridge at a constant temperature is best, but a couple of weeks at 30–50 °F (-1–10 °C) outside would help to force the formation of bitartrate sediment now, rather than after you filter and bottle. Of course, shield the wine from sunlight to avoid a light-struck flaw if you move it outdoors.
-Try a gum arabic product to retard crystal formation and color precipitation: Funny that you should write with your sediment problems in the same issue that our friend, G. Weiler (question on page 16) mentions that they’d like to try a gum arabic product to help with excess tannins. Even though you’re not dealing with a sensory issue (tannic wine), gum arabic and related arabinol products were also developed to help with cold stability. Their high molecular weight and highly branched carbohydrate polysaccharide structure hamper the precipitation of both colored material and bitartrate crystals in bottle-ready wine.
It’s important to do bench trials to see the effect on the wine with any addition. Because you’d be adding gum arabic for stability reasons and not to enhance mouthfeel or mask tannins, I’d recommend the medium to higher dose rate, or 0.5–1 mL/L. As I describe earlier, measure out some 50 mL aliquots of your wine, dose in the 0.5–1 mL/L range, and see what the effects are. If the 1 mL/L rate doesn’t deliver any negative sensory effects, I’d be tempted to go with the higher rate. Read each manufacturer’s directions but in general, gum arabic adds are made after final filtration and before bottling. I like to wait at least 72 hours between addition and bottling. Good luck!