Keeving is a traditional way to produce a naturally sweet cider by clarifying the apple juice. Enzymes create a floating ‘brown cap’ thats traps yeast and impurities so the clear juice can be syphoned off from underneath. This hobbles the fermentation so that the cider keeps some of its sugar. It produces a soft, round drink, low in tannins and with a slight sparkle.
The French use keeving to make cidre bouché (meaning cider with a cork). Unfortunately, they call the process defecation, but don’t let that put you off. Keeving nearly died off commercially in Britain but the good news is that a few craft cider makers are reviving it.
Start in late November with mature apples
Basically, you scrat or mill late-maturing, apples (mainly bitter-sweets) on a cold day, leave the pulp to macerate, then expose the juice to wild yeast. Traditionally, with the right choice of apple and a bit of luck, gel rises and forms on the top of the must after a few days. This ‘brown cap’ sucks up carbon dioxide and some of the yeast and nitrogenous nutrients that feed it. Today, we rely slightly less on ‘muck and magic’ and help this along by adding in a natural enzyme and some calcium.
Allow the pomace to macerate for a day
At the beginning, the sugar level should be at least 12% (SG 1.055). Store the fruit until the temperature is around 5C and expected to stay there for a week. Wash and scrat the apples, then stand the pomace for 24 hours. Press the pulp. Don’t add yeast; the whole idea is to slow down the fermentation.
Help build your ‘brown cap’ with PME and calcium
Letting the pomace (pulp) stand for a day after scratting allows enzymes in the apple flesh to go to work and a chemical change called demethylation to take place.
But to make the formation of the brown cap or flying lees more likely it can be nudged along by adding PME, an enzyme that occurs naturally in apples, and a small amount of food-grade calcium chloride.
The pectin methyl esterase helps the gel form by de-esterifying the pectin. Calcium combines with the chemically altered pectin in the juice and helps the pectate gel thicken. The two are added separately.
Where to source your enzymes
You can buy a kit containing concentrated PME and calcium chloride from Vigo at £14.50. The 1000 litre Vigo Keeving Kit consists 14ml concentrated PME solution, 500g of hydrated calcium chloride flakes and a 1ml syringe for accurate measurement.
Add PME and calcium separately
You add the PME to the container before the juice so that it is properly mixed. The recommended dose for the enzyme solution is 1.0ml to 1.5ml per 100 litres of juice, but you might need larger doses at temperatures below 10°C.
A day or two after pressing the juice and mixing it with the enzyme, take a sample of the treated juice in a clear container. You’ll need to add 1ml of 40% calcium chloride solution to one litre of juice. If it produces a fine cloud suspended particles after about a minute you can thoroughly mix the calcium chloride into the juice.
If not, cider scientist Andrew Lea advises repeating the test after three, six and possibly 12 hours depending on the temperature of the juice. The maximum dosage of calcium is 400 parts per million (4g in 10 litres).
Don’t confuse PME with pectinase
A few caveats: the PME you use must not contain any trace of a depolymeriser. Don’t confuse PME with pectic enzyme, pectinase, or pectolase, which are used to clarify non-keeved ciders. PME and calcium chloride must never be added together. If you can’t get hold of the enzyme just use the calcium chloride. You should keep PME in the fridge. If its old you may need slightly more. If you can’t get food-grade calcium chloride you can substitute ground chalk and table salt. In the old days they used ash.
Leave room to top up
Fill the vessel to about 85% of its volume to leave room for the brown cap. (Say, 25 litres in a 30 litre bin or demijohn, for example). About a fifth of the volume will be lost to the brown cap so you’ll need to set aside some juice for topping up or when you’ve racked it off. You don’t need a hermetic seal but you will want a lid to protect the must while you’re keeving.
Ferment your cider slowly under airlock
If keeving is successful, though, rack or syphon off the clear juice – the bit between the brown cap and the lees. Ferment it under airlock. Sample it from time to time and rack it again to slow fermentation, with a view to bottling at around SG 1.015 (medium-sweet) or SG 1.010, when the fermentation is imperceptibly slow – this should not be a loss of more than two points SG over three weeks, according to Andrew Lea.
Racking will slow, then stop fermentation
Repeated racking stops the fermentation, beginning at SG 1.030. You will need to rack about three times, topping up each time with fermented juice. The Canadian ciderist and author Claude Jolicoeur recommends racking at two to four points higher than the SG you’re aiming at. So, at 1.018 to achieve and a final SG of 1.015, for example.
Bottle when the air pressure’s high
It can take up to a year before a keeved cider is ready to bottle. Eventually, bottle it on a cool, high-pressure day when the air pressure helps minimise suspended yeast and keeps up the amount of carbon dioxide dissolved in the cider. Use sturdy, champagne-type bottles and store them upright. Then wait while the cider conditions.
Typically, the specific gravity of a bottled, keeved cider will drop by around five points as it conditions. You’ll have a cider with an ABV of around 4.5%.
What do if keeving fails
If the cap is white, keeving has failed but you can ferment your cider in the usual way. Some varietals can’t be keeved; no head forms. Apparently, Kingston Black seldom keeves despite being the ‘almost perfect’ cider apple, although this is disputed.
What to do to if your fermentation has stuck
Keeving is a slow process but if you are certain that your cider has stuck at too high an SG then you can add a small dose of nutrients to move it along. Try a tiny amount (02.ppm or 02.mg per litre) of vitamin B1. There is a risk, though, that the fermentation will start up again in earnest and go right through to dryness. Adding a cultured yeast should only be a last resort.
Other ways to make sweet cider
There are other ways to achieve a sweet cider. Multiple rackings will give you a good off-dry or medium cider, assuming your fermentation is already fairly slow.
If you add sugar or dextrose to a dry cider at bottling time you will get what’s called an unstable sweet cider which you will need to keep chilled and drink within a month. (A week at room temperature). There’s a chance that the fermentation will kick off again in the bottle.
One way to get around this is to pasteurise your cider after bottling but, frankly, if you’re going to do that you might as well buy a commercial cider. Likewise, adding an artificial sweetener such as sucralose or saccharin, which will give a stable cider but will leave a nasty back-taste. One final method is refrigeration close to freezing point but you’d need special and expensive equipment for this of the type used to stabilise ice cider.
In the UK, commercially produced, keeved ciders include Pilton Somerset Keeved cider. Cokagee Keeved Cider from Slane claims to be Ireland’s only keeved cider and has won prizes at The Royal Bath and West and the Hereford Cider Museum International Cider & Perry Competition among other competitions.