At this time of the year I’m watching the SGs of the keeved ciders
almost day by day, in order to establish when it will be safe to
bottle. We discussed this here last year and a useful rule of thumb
came to light. If I’ve remembered it incorrectly, please somebody put
me right, but I believe that if a one point drop of SG takes a period
of 10 days or more, it can be taken as an indication that the SG is
bottoming out and that it is safe to bottle.

The implication is that for keeving it is important to be able to read
SG to within a degree and therefore reading errors do need to be
considered. I’ve looked in vain for some figures. David please
enlighten me. Say for example the ambient temp is 10 C, how is the
hydrometer reading affected? Regarding errors due to stratification,
that is something that I never would have even thought about. Thank
you Gary, it is good to be aware of it. I will have a gentle stir
before measuring in future, if notable changes in temperature have
occurred.

Continuing the experimental 50/50 blending of the keeved Porters and
Yarlington, I’ve progressed from the demijohn and now have a 120 litre
tub of it. Like the demijohn, this is also holding at 1012. As the
two ciders were well mixed during their blending, I needn’t worry
about stratification. Since the weather has stayed the same for two
weeks, around 15 C every day, there is no difference between
hydrometer readings due to temperature. Another week of similar
readings and perhaps I will feel confident enough to bottle!

I’m looking forward to bottling because I’m dying to try out Barry’s
corker, that he has kindly lent me.

Rose.

On 19 Mar 2009, at 11:11, Gary Awdey wrote:

> On Tuesday, March 17, 2009, David Llewellyn wrote:

>> Apart from the accuracy problem of actually determining small
>> differences while reading along a scale, if the
>> temperature of the cider was much lower at the time of the first
>> reading (ie the cold weather we had weeks ago), it might have accounted for an
>> apparent small change in SG, unless you corrected the readings to 20 degrees
>> C for example. The lower the temperature of the liquid, the higher the SG
>> reading will be, so you have to correct to a standard temperature. Sorry if
>> you have already taken this into account!!
>
> Another cautionary note (with more apologies if you’ve already taken
> this into account) is the effect of stratification. In the past I’ve
> occasionally noted odd readings that go counter to what would be
> predicted by the temperature density effect David mentions. When it is warmer
> you would expect density (and gravity readings) to be lower. What I’ve
> found is that sometimes the warmer weather makes fermentation of keeved
> ciders more active with the result that it is de-stratified. Measurement after
> racking is also occasionally higher than measurement before (I generally take
> samples from near the top). Heavier cider, richer in sugar, is
> mixed up from the bottom when fermentation is more active. This phenomenon is
> mentioned in several winemaking books so evidently it is not
> particularly unusual. When an accurate gravity reading of the entire batch is
> needed (which is admittedly not very often) I make sure the cider is
> adequately mixed by stirring or sparging with carbon dioxide gas (taking care
> not to introduce oxygen at the same time). However I don’t attempt to
> destratify cider that is still sitting on top of deposits that might be
> disturbed. I usually mix blended ciders thoroughly before measuring gravity.
> Otherwise measurement tends to be skewed toward the low side (and presumably the
> opposite would be true if samples were obtained from the bottom of the
> vessel).
>
> Similarly, if two keeved ciders are mixed and fermentation is very
> slow (as one would hope it would be) then you may start with a well mixed
> blend but see measured gravity drop unexpectedly quickly as stratification
> occurs. This would seem to be more likely as a cause of possible measurement
> error if you see a notable drop in gravity without seeing a corresponding
> amount of gas escaping at the airlock.
>
> Gary Awdey
> Eden, New York