It is more satisfying, however, to allow the fermentation itself to generate the carbon dioxide by 'natural conditioning'. One way of doing this is by racking and bottling the fermentation early, say at a gravity of 1.003, and allowing the cider to finish fermenting and to mature in the bottle. The CO2 produced will dissolve in the cider to produce bubbles when the bottle is opened. A drawback to this technique is that the yeast deposit in the bottle may be rather heavy and coarsely flavoured. An alternative is to rack the cider into bottles after fermentation to dryness, adding a small amount (10 g per litre) of priming sugar to each bottle, and allowing a secondary yeast fermentation of the added sugar to produce the gas. This can be very successful although the bottom of each bottle will inevitably be a little cloudy when poured, because there will always be some yeast deposit which will be roused up when the pressure is released. This problem can be lessened on a domestic scale by storing the conditioned cider in a pressurised keg or barrel similar to those used for home-made beer. In these devices the yeast drops to a below below the draw-off tap and a bulk, sparkling and clear cider is easily achieved. The ultimate way of avoiding the yeast problem is to produce a cider by the 'methode champenoise', in which the yeast is removed by inverting and turning the bottle in stages until it is all collected in the neck. This is then frozen in an ice-salt mixture, the bottle is opened, the frozen yeast plug is forced out by gas pressure, and the bottle is topped up and resealed before the majority of the gas can escape. The quality of such ciders is legendary, although for obvious reasons they are labour-intensive to produce and therefore expensive to purchase!
Any bottles used for carbonated ciders must be designed to withstand the pressure generated by the gas, or there is a serious risk of them bursting and causing injury (not to mention the mess!). Some years ago there used to be quart cider bottles with internal screw threads and special threaded stoppers, but these no longer exist. An alternative is to use glass beer bottles which are sealed with a crown cork - these and the capping tools are widely available from home-brewing suppliers. The industry has now gone over almost entirely to PET (polyethyleneterephthalate) bottles which are lightweight and hold a moderate pressure well. Also, if they do burst, there is no risk of injury from flying glass. If you are making a small amount of cider for home use, you can recover, rinse and re-use these bottles several times if they have previously contained other carbonated drinks. If you cannot scrounge sufficient secondhand bottles or you are working on a larger scale, you may have to buy new PET bottles from a specialist supplier. Non-carbonated ciders can of course be bottled in wine bottles with regular corks if required, but the bottles must be stored on their sides to prevent the corks drying out and the air getting in (which will cause spoilage). Normal plastic (PET) bottles do allow oxygen in through their walls and so the flavour of the cider does alter over time compared to natural conditioning in glass. However, there are PET bottles sold into the home brew trade which do incorporate an oxygen barrier e.g. Coopers Oxbar brand, and it is well worth hunting these out.
If you don't want to pasteurise a sugar-sweetened cider, then your only reliable route is to use a non-fermentable synthetic sweetener instead of sugar. Saccharin has been used to sweeten UK 'farmhouse' ciders since the 1890's - for so long, in fact, that many unsuspecting people believe it to be a traditional and natural ingredient. However, saccharin also has a nasty liquorice taste and a long bitter aftertaste. The most successful artificial sweetener is the more recently introduced sucralose, sold under the brand name "Splenda". The small compressed tablets are each equivalent to one teaspoon of sugar in terms of sweetening power and are ideal for just one glass of cider at a time, although they do not have the 'body' of sugar. Other sweeteners you might wish to consider as an amateur are extracts of the herb Stevia (which is a high intensity natural sweetener) and Xylitol (which is a non-fermentable sugar alcohol with about the same sweetening power as sugar). Both are safe but neither are permitted for sweetening of commercial ciders in the EU at the present time.If you really want to sweeten dry ciders with added sugar (or with frozen or concentrated apple juice) but you do not want to pasteurise or filter them, it is important that they should be racked and stored for several months after fermentation is complete, to allow the yeast to die out completely before the sugar is added. Otherwise the risk of re-fermentation is considerable; almost inevitable! The chances of re-fermentation can be somewhat reduced by the addition of yeast inhibitors such as potassium sorbate and benzoate at levels up to 200 ppm. (Both these materials occur naturally in rowan berries and cranberries respectively). Potassium sorbate may be bought from home winemaking suppliers. It is most effective if combined with say 50 ppm of SO2 added at the same time. In the absence of sulphite, sorbate is not so effective and may also lead to 'geranium-like' off-flavours in the presence of malo-lactic bacteria. But to be honest I do not advise the 'preservative' route for long keeping of sweetened cider - the risk of instability and explosion is just too great. If you are using apple juice concentrate for sweetening, be aware that this is not sterile and contains osmo-tolerant and preservative-resistant yeasts such as Zygosaccharomyces bailii which will grow quite happily in the presence of sorbate and SO2.
It is best to choose days on which the barometric pressure is high for these operations, since this will help to keep suspended yeast to a minimum and will retain the maximum amount of dissolved carbon dioxide in the cider. The success of the whole process depends on reducing both yeast and nutrient levels to a minimum so that re-fermentation of the remaining sugar is unlikely to take place. Sweet ciders of this sort may have a slight 'prickle' to them, particularly in bottle, since a slow fermentation may continue to generate carbon dioxide. The procedure described is ideal for single-variety demonstration ciders or for those which need no further blending - the flavour tends to be 'fruitier' since the sweetness is derived from unfermented juice rather than from added sugar. The alcohol level in the cider is of course less than if it had been fermented to dryness because only a part of the sugar has been converted. Ciders which do need blending (see below) are best fermented all to dryness first, before blending and finally sweetening after a further period of storage.
The trial blends which are now balanced for tannin can be blended for acidity following a similar routine. If the addition of acid is required, malic acid may be used in 0.1% steps. Removal of acid is difficult at this stage, but may be done if necessary by the addition of potassium carbonate - calcium carbonate used here tends to leave a residual chalky flavour in the cider. The trial blends now have the correct tannin and acid balance, and they can finally be corrected for other more subtle flavours and aromas by blending amongst each other. Finally, the main bulk of ciders can be blended according to the proportions determined by the trials but without the addition of the sugar at this stage. For reasons explained above, the ciders must be allowed to stabilise further in bulk store before correcting the sweetness (unless filtration and pasteurisation are used to prevent all possibility of re-fermentation).
A blend of fully ripened sharp and bittersweet fruit is used for these ciders, taken from mature orchards which are naturally low in nutrients but fairly high in tannin. Dessert fruit is much less likely to be successful here, due to its generally low tannin and high nutrient levels. The sugar level should be at least 12% (SG 1.055). The fruit is stored until a cold day late in the year when the temperature is about 5o C and expected to remain so for a week or more. The fruit is washed and milled in the normal way, but the pulp is then packed into barrels (or, better, plastic containers) to stand for up to 24 hours. This is the procedure of 'maceration' or 'cuvage', terms with no particular English equivalent. During this time, oxidation slowly proceeds which develops the juice colour, and pectin leaches out of the apple cells into the juice. The juice is then pressed out, rich in colour and thick in texture, and is run into clean tanks which are allowed to stand without sulphiting or the addition of yeast (author's note: If the pH is around 4, which it is likely to be, I do actually add 100 ppm sulphite at this stage to provide some inhibition of bacterial infection. The 'official' French recommendation is to burn 10 grams of sulphurated string in the barrel!!)
Since the temperature is low, no significant yeast fermentation takes place, but the natural pectic enzymes in apple juice slowly change the pectin to pectic acid. This forms a gel with the natural calcium in the juice and a 'brown head' (the 'chapeau brun') rises slowly to the surface. Some of the pectin also combines with juice protein and tannin and falls as a sediment to the bottom, leaving a clear juice between the two. To make this process more reliable, a mixture of calcium carbonate (3 g per 10 litres) and sodium chloride (4 g per 10 litres) is often added to the fresh-pressed juice - the calcium helps to form the gel, while the chloride helps to inhibit the growth of any yeast (author's note: I add 400 ppm (4 g per 10 litres) of calcium chloride which is a one-shot way of achieving the same thing). A specially prepared pectin methyl esterase enzyme (which is not the same as a regular pectinase) can also be added as described here. This process is known in French as 'debourbage' or 'defecation' (for obvious reasons!) and in English as 'keeving', and generally takes about a week. If things go wrong, and a yeast fermentation starts too early, a 'white head' (the 'chapeau blanc') is formed. This means that the whole vat has become turbulent and the keeving has failed!
If the keeving has been successful, however, the clear juice between the top cap and the bottom sediment is very carefully pumped or syphoned into a fermentation vat. It is now allowed to ferment under an air-lock in the normal way (with its own yeast), but this fermentation will be very slow because most of the nutrients in the juice will have been left behind in the 'brown head' and in the sediment. In fact, scientific study has shown that the pectin and the amino nitrogen nutrients are reduced by at least 50% during keeving. With such a slow fermentation it should be no problem to make a naturally sweet cider, by racking at S.G. 1.030 and proceeding as described earlier. Preferably the ciders should be bottled in crown-cap beer bottles which are stored in a cool place for maturation -they CAN get quite fizzy if allowed to warm up too much during the summer!
The advantage of this process is that it can produce a naturally sweet and well-coloured cider, brilliantly clear due to the removal of pectin during keeving, and full of flavour because of the low nutrient levels during fermentation. The disadvantage is that a lot of it depends on luck - the correct fruit, cold weather, benevolent strains of wild yeast and freedom from bacterial infections! What actually happens is that the fermentation begins with so-called apiculate' yeasts from inside the apples predominanting - these then slowly die out as the alcohol level rises and the Saccharomyces ( wine yeasts') slowly take over to complete the job. If you get the chance to look at the yeasts under the microscope, as I have done, you'll see all shapes and sizes of organisms imagineable. This is quite different from a fermentation with an added yeast, where all the cells are identical.
(Author's note: In my experience, the flavour immediately after even a well-conducted 'natural' fermentation is heavily dominated by ethyl acetate, and can be really quite unbalanced and unpleasant to drink. A few months storage in bottle, however, can work wonders in blending out these flavours to something really magnificent. Not everybody likes it, though - a friend of mine described my best quality cider as 'tasting like smoky bacon' (which is due to the natural tannins breaking down to give 'spicy' flavours)!!)
There is plenty of scope here for anyone who wishes to experiment with different parts of the process. For instance, the final colour and clarity of the cider is critically dependent on the length of 'cuvage', during which the oxidising enzymes produce colour from the tannin, and the pectin slowly migrates out of the fruit into the juice. If the pulp is held too long a time, the rich orange colour of the final juice will actually diminish and the flavour will become insipid due to excessive adsorption of oxidised tannin back onto the pulp. If the pulp is held too short a time, not enough pectin will migrate out into the juice to form a good 'head' during subsequent keeving and so, paradoxically, effective clarification and nutrient removal will not be achieved. If the pulp is tightly packed and too little air is present during 'cuvage', too little colour will be developed - but if the pulp is loosely packed and too much air is present, spoilage organisms (vinegar bacteria) will quickly take hold. If the weather is too cold, none of the desirable enzyme activity will take place - but if conditions are too warm, yeast fermentation will begin too early and the keeving will fail. If the pH of the fruit is too low (less than 3.6) the natural pectinase activity may be too slow to form a successful 'brown head' - but if the pH is too high (greater than 4) undesirable film yeasts will develop to the detriment of the required Saccharomyces species.
Balancing these factors (and many more) relies on judgement and experience and was part of the skill of the traditional cider maker, although he knew nothing of the biochemistry behind it. The new traditionalist should be able to build on this skill the better, if he only bears in mind the scientific principles of what he is trying to do!
So far we have considered cidermaking when everything goes according to plan. In the next part of the series we shall look at some of the more common things that may go wrong, and what we can do about them.
© Andrew Lea 1997. Lightly updated 2009
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