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THE SCIENCE OF CIDERMAKING

Part 5 - When things go wrong

So far we have looked at cidermaking when everything goes according to plan. Inevitably, however, there will be occasions when things don't work out as expected, so in this section we shall look at various problems and some possibilities for their solution.

Slimy Pulp

If you are lucky enough to have genuine cider apples to use, and they're not stored for too long, you are unlikely to have problems with slimy pulp. True cider fruit has been selected over many generations to press cleanly and to leave a dry and handleable pomace (which is another good reason for using it if you possibly can). Remember, though, that the pulp should not be milled up too small, even with genuine cider apples - we are not aiming for apple-sauce! The ideal size for pressing is little nuggets of apple each about the size of a pea, which gives the best compromise between juice yield and ease of pressing.

With dessert apples, however, no matter how carefully you mill the fruit, there is always a tendency for pectin to leach out of the cells and to be partially broken down by the natural fruit enzymes while pressing. This is particularly true if the fruit has been stored for any length of time. The result of this is a 'cheese' of slimy pulp, which clogs up the press-cloths and makes it impossible to get a decent yield of juice. 'Golden Delicious' is especially bad in this respect. Under these circumstances you may find that light continued pressure over many hours gives you a better result than a hard quick squeeze. Even so you may have to resort to other measures. In the USA, 'press-aids' such as wood pulp or rice hulls are sometimes used, mixed with the apple pulp to provide better drainage pathways. An alternative is to press mixed loads of fruit if you can, the better with the poorer. If you can press a mixture of desserts and bittersweet, the tannin and the superior structure of the bittersweets will help to offset the poor characteristics of the dessert fruit.

The best solution is to apply a pectic enzyme to the pulp. In this case, you are aiming to complete the total breakdown of the pectin, to overcome its partial breakdown in the apple which is causing all the problem. You can use the same type of pectolytic enzyme which we described earlier for juice preparation, although the dosage rate will need to be about twice as high. The enzyme should be well-mixed with the pulp and allowed to stand, at 55 C for 2 hours or at room temperature for up to 24 hours. For most people, an overnight incubation in the cold will be the most practical solution. Next day, the pulp should press cleanly and easily, and you won't then need to add any more enzyme to the juice before you start to ferment. This technique is suitable for mainstream cidermaking - it cannot of course be used if you are trying traditional 'keeving', because the pectin will be broken down too far and you will upset the natural balance of the juice. (In France, however, it is possible to buy special pectolytic enzymes which are suitable for keeving procedures).

Fermentation and storage problems

We have previously mentioned the effects of temperature, nutrients and so forth on fermentation, the possible use of sulphur dioxide, and the need to keep air out of the system. In a good and active fermentation, few problems should arise if these precautions are observed. In slower fermentations or in early storage, there are three classical microbiological problems which may crop up.

Film yeasts (generally of the genera Candida, Pichia or Hansenula) will readily contaminate a slow and unsulphited fermentation, or a stored cider where the air has been allowed to get in. The organisms are present on the fruit and thrive in aerobic conditions, so they sometimes appear on the top of the liquid where they will start to break down the alcohol. Their presence is often detected by a strong smell of ethyl and amyl acetates, reminiscent of the solvents used in nail-varnish remover. In small amounts these compounds are important contributors to the overall flavour of cider but as soon as they become obvious then you have a problem. Sometimes more unpleasant musty or oxidised flavours are formed instead. The yeasts themselves form a greasy/powdery film on the surface of the cider, breaking up into small white sheets and dropping to the bottom of the vessel when disturbed. Prevention is better than cure but, if film yeasts take a hold, keep the vessel well topped-up to exclude air and add 100 ppm SO2 to keep the organisms in check. The cider may still be usable if infection has not gone too far but extra care must be taken during handling to make the conditions for their growth as unfavourable as possible. Vessels where infection has occurred should of course be properly sterilised before re-use.

The picture to the left shows a film yeast on stored cider. It has been deliberately pushed aside gently with a finger to show how the film 'rucks up' in a characteristic manner.

Acetic acid bacteria of the Acetobacter family are often confused with film yeast because they too tend to grow on the surface of poorly stored ciders. They oxidise the alcohol to acetic acid directly and so the cider smells and tastes of vinegar rather than of solvent. Acetobacter tend to form jelly-like sheets on the top of the cider - these do not break up when shaken but fall to the bottom all in one piece. They are aerobic organisms just like the film yeasts, however, so the same preventative and remedial measures should be effective. If the cider is too acetified for your taste, it can be neutralised by the careful addition of potassium carbonate. Alternatively the cider can be stored in a tightly sealed container until next season, when it can be blended back in with fresh pomace at the rate of 50 litres per 50 kg and re-fermented with a fresh yeast inoculum which may consume some of the acetic acid. The same technique may be worth trying for ciders affected by film yeast.

It has to be said that many so-called 'farmhouse' ciders are quite badly acetified, particularly the poorly-made 'scrumpies' which are sold to unsuspecting tourists in the West Country. There is probably some truth in the assertion that older generations of cider-drinkers became conditioned to these flavours since they were an integral part of the rough ciders which were then on offer. The same was probably true of wines until the widespread adoption of glass bottles and cork closures in the eighteenth century. Nowadays, however, most of us would regard acetified flavours as undesirable, and it is certainly quite possible to make a fine and well-flavoured 'traditional' cider without them.

Cider 'sickness' is a disorder caused by bacteria of the genus Zymomonas (other types of which are utilised in the tropics for the production of palm wine). These organisms ferment sugars in the same way as yeasts, but they also produce large amounts of acetaldehyde which is said to give an odour of lemon or banana skins. In France, this disorder is known as 'framboise' since the odour is regarded as raspberry-like! The acetaldehyde also combines with the cider tannin to give a milky haze and the cider quickly becomes insipid and 'thin' in body. This problem only affects sweet ciders or those with residual sugar which are also low in acid (pH higher than 3.8), which is one good reason for fermenting and storing all ciders dry. Ciders which are naturally sweet and low in acid (e.g. French traditional) are obviously under greatest threat from this organism. Unfortunately it is totally resistant to SO2 so there is no easy control. The normal recommendation if ciders begin to become sick is to raise the acidity to 0.5% and to add an active fermenting yeast complete with nutrient. You will lose your sweet 'sick' cider but with a bit of luck you may end up with a much healthier dry one which will be some recompense! If the sick cider is already in active bacterial fermentation you will just have to let it take its course and then fine it and blend it off when all the sugar has gone. Once again, all equipment which has been in contact with cider 'sickness' should be well sterilised before re-use.

Other storage problems

Ropiness or oiliness is a curious condition which occurs sometimes in low acid ciders in bottle or in store. When the cider is poured, it assumes the consistency of a light oil or of a slimy ropy texture like raw egg-white, although the flavour is not much affected. This is due to the slow growth of certain forms of lactic-acid bacteria which produce polysaccharide gels (similar to those formed by related bacteria during yoghurt-making and which provide its texture). Ropiness does not generally occur where SO2 has been used. It can be ameliorated if the cider is transferred to an open vessel, well stirred to break the gel and treated with 100 ppm of SO2. Fining with bentonite and gelatin (see later) may also help to bring down the bacteria and the gel.

Mousiness is unmistakeable to those who have tasted it, although individual sensitivity varies widely from person to person. The flavour is best likened to that of a mouse-cage, although some people think it is closer to bread or freshly-baked biscuits. Strangely enough, the chemical compounds responsible for all these flavours are identical! This defect arises from a slow microbial action in storage, and although its chemistry is generally understood nobody knows why it happens in some ciders but not in others. Unfortunately there seems to be no reliable way of preventing its formation or of removing it once formed, although it is generally less common in ciders which have been sulphited, and access to oxygen appears to encourage it.

Discolouration of ciders (apart from the normal golden-orange colour of partly oxidised tannin) is nearly always caused by metals. Iron gives rise to blackening and copper gives greener hues, due to reactions between the metal, the tannin in the cider and the oxygen in the air. Often the colour does not develop until a bottle is opened and the air can get in - the colour then develops in minutes or hours. To confirm this, a pinch of citric acid may be added to a freshly-opened control sample. If this darkens at a significantly slower rate than the problem bottle, then iron is the probable cause. There is not much that can be done to cure the problem although re-bottling in the presence of citric acid may be considered. A technique known as 'blue fining' can be used on a commercial scale to remove the metal but only in the hands of a trained chemist. Such problems will never arise if the proper sort of processing equipment is used so that free iron and copper cannot get into the cider.

Hazes and Deposits

Many people making a traditional product will be quite happy with a certain amount of haze in their cider. There are, however, degrees of acceptable cloudiness and if you have gone to a lot of trouble to make a sparklingly bright cider it is very annoying to have it develop a haze or a sediment later. There are a number of possible reasons for this.

Microbial hazes are caused by various spoilage yeasts or by heavy infestations of bacteria. Most of these have been covered above although there is one slow-growing yeast (Saccharomycodes ludwigii) which forms clumps at the bottom of the bottle in sweetened ciders without affecting flavour very much. Generally, microbial problems should be avoided by proper attention to cleanliness and hygiene. The only reliable way to tell whether a haze is microbial in origin is to look at it under a high-powered professional microscope (500x magnification). This is hardly practicable for the domestic cidermaker unless you have a friend or colleague with access to a laboratory. If you do, ask them to look for yeasts (about 10 microns in size) or for bacteria (about 0.5 microns in size but often in pairs or in chains).

Pectin problems were mentioned in an earlier section. Apart from the 'slimy pulp' issue, pectin can also cause hazes in finished product, since the pectin is insoluble in alcohol and can slowly come out of solution during and after fermentation. Sometimes this takes the form of an overall cloudiness which is impossible to clear. At other times it forms wisps or strands in the bottle which tend to break up when shaken or disturbed.  If you want to be sure of preventing them, you must use a pectolytic enzyme which is added at the beginning of fermentation. If you think you have a pectin haze in the finished cider, add one part of cider to two or three parts of methylated spirit in a small glass and shake well. The pectin will form a gel or a clot, or possibly strings if there isn't much of it there. If pectin is confirmed, you can try adding some pectolytic enzyme to break it down although it won't be so effective in the presence of alcohol. Otherwise you must just live with it and remember to do better next time!

Tannin hazes are sometimes the most frustrating, because they may develop in store in ciders which may have been bottled completely clear. They occur particularly in ciders made with bittersweet fruit where the tannin levels are relatively high. Over time, these tannins polymerise together to generate large molecules which eventually become so big that they drop out of solution. Sometimes they form a haze, while sometimes they coalesce to a compact sediment. Often they cause a 'chill-haze', where the product becomes cloudy when put in a refrigerator for summer drinking but was quite stable at room temperature, or they may appear during winter storage if the cider was bottled before a snap of cold weather (a warming and cooling cycle is a good test to indicate potential tannin haze). The tannins are also responsible for much of the 'bite' of traditional bittersweet ciders so it seems a pity to remove them. Sometimes, however, bittersweet ciders may be so bitter or astringent that it is worth lowering the tannin levels for reasons of taste, as well as for haze stability. The 'fining' procedure below can be used for either. It can also be used for gross clarification before sheet filtration or racking, or perhaps to remove 'ropiness' or 'sickness' bacteria. Do remember, though, that fining a low tannin cider will make it even more insipid.

Fining

All alternative way of clarifying ciders is by the use of ‘fining’. There are many different ways of fining although the principles are the same for all. The tiny particles of beverage haze are electrically charged which is why they do not coalesce, because 'like charges' repel each other and keep them in suspension. If we add a material with an opposite charge we can neutralise the charges so the particles will then clump together and settle out. In ciders the tannin or other particles of debris tend to be negatively charged, and so we add a positively charged material which is usually a protein. Traditionally, egg white or fresh slaughterhouse blood was used - one egg will treat about 10 gallons of cider! Nowadays special gelatins are used to provide the protein. If too much gelatin is added, the cider becomes 'overfined' and we get a gelatin haze instead, so it is wise to add some bentonite at the same time. Bentonite is a negatively charged clay which mops up any spare gelatin. Appropriate grades of gelatin and bentonite are available from specialist winemaking suppliers. Do not use domestic ‘cooking’ gelatin which has quite the wrong physical properties. Do not use isinglass as a fining in cider – it works well for beer but has the wrong properties for cider due to the difference in pH. Bentonite on its own is often used as fining to remove protein hazes from grape wines, but ciders contain much less protein and protein hazes do not  form, so bentonite alone is of little value to the cidermaker. 

Ideally it is best to run tests to find out how much gelatin and bentonite are required in a particular situation. Also, because fining with gelatin will tend to remove some tannin from a cider (and is sometimes done deliberately for this purpose), small scale trials are essential before treating a large bulk of cider. For instance, a 1% stock solution of gelatin should be made up in warm (not boiling) water, and a 10% stock slurry of bentonite should be creamed up separately in warm water too. Then set up a series of six flasks each containing 200 ml of cider and an appropriate amount of bentonite as shown in the left hand columns of the Table. The appropriate volumes of gelatin solution are then added from a pipette or a small syringe as shown and the flasks are well shaken. After leaving for several hours, the flask which gives the greatest amount of clarification with the least amount of ingredients should be chosen for scale-up according to the right hand columns of the Table. For full scale fining, the bentonite should be creamed up in a small quantity of cider and then well distributed in the bulk. The appropriate amount of gelatin should be made up as a 5% solution in warm water and added to the bentonite-treated cider in a thin stream with constant stirring before being allowed to settle for several days. If the main purpose of the exercise is to reduce tannin levels, rather than to clarify the cider, the gelatin solution should be added first, allowed to stand for two hours after stirring and then followed by the bentonite.

After fining, a deposit will be thrown and a clear cider should remain above it. This can then be racked off, filtered and bottled accordingly. The handling involved during fining will obviously cause some aeration which should be kept to a minimum for all the reasons previously discussed. The addition of 50 ppm SO2 at this stage will also be helpful to prevent oxidation.

Cider Fining with Bentonite and Gelatin

TEST (per 200 ml cider)

FULL SCALE (per 100 l of cider)

Bentonite
(ml of 10% suspension )

Gelatin
(ml of 1% solution)

Bentonite
(grams)

Gelatin
(grams)

1

1

50

5

1

2

50

10

2

2

100

10

2

4

100

20

4

4

200

20

4

8

200

40

A more efficient substitute for bentonite, which has been around for over 50 years but until recently not widely available, is a colloidal silica known as ‘kieselsol’. This now seems to be readily available from the special winemaking suppliers, and forms much more compact bottoms and much more quickly than bentonite.  If the kieselsol is supplied as a 30% solution, it should be diluted to a stock solution 1:10 with water and used in place of the bentonite in the test fining above. For full-scale fining, the kieselol should be used undiluted at the same rate given as for bentonite.

 
Another modern fining agent, which may be used on its own or in combination fining as a gelatin substitute since it is positively charged, is called chitosan, and is prepared from crab shell and other crustacean waste in the
USA and the Far East. The chitin (a polymer of N-acetyl glucosamine) which forms the animals’ exo-skeletons is treated to de-acetylate it and this yields chitosan. It has several specialist medical applications especially in the field of wound dressings. As a fining agent, chitosan is becoming more widely available from the specialist beverage suppliers, and works well in ciders. Dosage rates for individual preparations should be obtained from the suppliers.

 
Fining for clarification of commercial ciders is not longer so common as it was since the advent of cross-flow ultrafiltration. However, this is a costly technique and likely to be of value only in a factory situation, not for smaller scale craft use.


 Andrew Lea 1997. Lightly updated 2009

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