Sediment in Bottles, Causes
There are several potential causes of sediment forming after you have bottled your wine.
The first cause has to do with the wine appearing to have finished fermenting, but in fact not being quite done. If the wine still has a substantial amount of residual sugar left when it is bottled, it will carbonate and throw yeast sediment in the bottles. If you moved to the stabilising stage without checking that the specific gravity readings were stable for 2 consecutive days, the wine could continue to ferment in the bottles. This would not only cause sediment to be shed, but would also cause bubbles, which would force the corks up. The instructions for wine kits are generic, and some may quit fermenting at a specific gravity reading of .993. This is why you take 2 readings, to be sure it has finished.
If the wine has only 0.001¾0.0005 points of sugar left, it may seem finished, and the shock of being fined and stablised may clear it perfectly. Yet even after filtering, there will still be live yeast cells in the wine, and enough sugar for them to re-start. If there is any amount of unfermented sugar, and a live yeast presence, then it can show up in the bottles as sediment.
It’s a common misconception that sulphite and sorbate kill yeast, and that these substances should take care of the problem of extra live yeast still existing in the wine. But neither additive has the ability to decrease yeast populations. As long as there is a source of fermentable sugar and live yeast cells in the wine, no amount of sulphite and sorbate will prevent them from eventually refermenting, unless there is also a sufficiently high alcohol content to help kill the yeast cells. What sulphite and sorbate do instead is help prevent spoilage in wines that are already fermented free of residual sugar, by preventing the reproductive activity of spoilage organisms.
Poor Filtration or Bottling Technique
Another possible explanation for sediment is poor filtration or bottling technique. A small amount of sediment is hardly noticeable in a 23-litre/6-US gallon carboy. But when it settles in a 750 ml bottle, sediment shows very well indeed. So if you carried some sediment over into the bottles when racking, even a small amount will become quite visible.
The same thing applies to careless filtration as well: the majority of the filter pads we sell are not fine enough to exclude a high percentage of yeast cells. If sediment is sucked off the bottom of the carboy, the yeast cells will sail through the filter pads and into the wine. Again you have a case where sediment that’s barely visible in a 23-litre volume will be more than visible in the smaller bottle.
Keeping the siphon rod up off the floor of the vessel is a key factor when you are bottling or filtering. One item that can help prevent you siphoning sediment from the bottom is a siphon rod holder, which attaches the rod to the wall of the carboy. Using this holder, you can place the rod at any level you desire, and control the depth to which it goes as it approaches the bottom of the vessel.
Once there is only a litre or so of wine left at the bottom of the vessel, without stopping the flow you can direct the siphon hose into a couple of single bottles and then push the rod down to get the remaining wine. Depending on how well you redirect the siphon hose, this will transfer some sediment to the last bottle or two, at most. It will still leave you 27 perfectly clear bottles full of wine drawn well above the sediment bed. Leave that last bottle to settle for a day or so, keeping it apart from the perfectly clear bottled wine. You can use it later as sampling wine.
If you don’t have a siphon rod holder, however, your best course is to rack your wine off the sediment and into a clean and sanitized primary fermenter or carboy, just before you bottle it. Slowly lower the siphon rod down the side of the carboy, so you don’t suck up any sediment as you are siphoning the wine into the other carboy.
Sediment could also be a combination of bacterial growth due to low stabiliser levels and live yeast. As mentioned, neither sulphite nor sorbate kill yeast, but they do prevent the reproductive activity of spoilage organisms. So if the levels of these additives are not sufficient, bacteria could form.
Written by Phyl on April 4, 2011.