Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Cells of Leishmania donovani in co-culture with Trypanosoma brucei, were severely affected in their growth, resulting in swelling and subsequent lysis. Similar effects were also observed when Crithidia luciliae or Phytomonas sp. were co-cultured with T. brucei. Direct contact between the cells under investigation and T. brucei was necessary because T. brucei did not hamper the growth of the other trypanosomatids, when separated by a filter with 0.2 μm pore size. Examination of this phenomenon at the ultrastructural level, in a co-culture of L. donovani and T. brucei, suggests that the plasma membrane permeability is increased in the former, as a result of a close cellular contact between the two cell types.

1. Following the experiences gained from an earlier experiment, cheese were made at varying controlled pitching points and rates of scald, the experiment being done both with sweet milk and comparatively acid milk.

2. One of the two cheese made from each vat was submitted to physical tests at regular intervals during the ripening process and the other cheese, when ripe, were judged by a panel of experts who also, together with non-experts and routine analysts, gave judgements of firmness and ‘spring’.

3. Tables were drawn up in which the rank orders of the cheese for each objective physical test and subjective judgement are compared with one another.

4. With the possible exception of vapour pressure and ‘spring’, the effect of pitching consistency was much more marked than that of the differences in rate of scald although the latter were considerable. Many physical properties were well correlated with pitching consistency.

5. The cheese makers are shown to have a greater self-consistency as individuals in picking out replicates and as a group in their decisions as to the rank order, by comparison with the other categories.

1. Six cheese of Cheddar type were made under conditions as similar as possible, except that the consistency of the curd at pitching, and in two cases the rate of scald, were varied.

2. Chemical and rheological analyses, as well as measurements of moisture content and vapour pressure, were made on the cheese and also judgements of firmness under various conditions were given by cheese-makers, bakers and non-experts.

3. A table is given in which the orders of placing of the cheese are compared as between the objective tests and the subjective judgements. The cheese-makers and the non-expert testers gave, in general, characteristically different orders, the orders given by the bakers tending to fall between the two.

4. It appears that the consistency of the curd at the pitching point (W/h as determined by the Scott Blair-Coppen method) and probably the rate of scald, are prime factors in determining the firmness of the cheese.

5. The whole experiment is preliminary in character and it is intended to repeat it in an extended form in the near future.

1. The pitching consistency of some 470 cheese has been determined at one factory and the data compared with the subjective judgements of a skilled cheesemaker. The smallest difference in consistency which the expert can distinguish with a reasonable degree of accuracy (threshold) is compared with those for purely elastic and viscous bodies, and it is concluded that the consistency at pitching is judged mainly from the elastic properties of the curd. The good agreement between these thresholds substantiates the hypothesis that our test for pitching consistency is closely related to the requirements of the practical cheesemaker.

2. The connexion believed to exist between firmness of curd at pitching and acidity was not substantiated, in the case of Cheddar, by a statistical examination of the available data.

3. The most usual values (medians) for pitching consistency are compared for four different factories, and it is shown that differences in technique may be associated with the same pitching consistency and produce very similar cheese, but that in other cases good cheese may be produced from very different pitching consistencies. The important thing is that the pitching consistency should be known and controlled so as to be as constant as possible under given conditions.

4. A technique is described for measuring the force required to thrust a skewer into cheese. This force (S) is highly correlated with “body” judged subjectively by an experimenter who was aware of the fact that such a correlation was to be tried. Judgements of “body” made by expert cheese graders were not so correlated, but the interpretation of their judgements was inadequate, so that no definite conclusion can be drawn.

1. A method is described for measuring the consistency of cheese curd during the scalding process which has been found satisfactory with Cheddar, Cheshire, Leicester, Double Gloucester, Caerphilly, Kingston and Derby cheese and is probably applicable to some other varieties.

2. The property (W/h), taken as a criterion of consistency, can be measured within less than 1 min. and is highly correlated with moisture content except when abnormal scalding conditions produce an uneven distribution of moisture in the curd. The size of cut does not affect this correlation within wide limits, though both moisture content and W/h are regularly affected by size of cut until the curd is approximately ready to pitch, at which point both properties show unique values independent of size of cut.

3. When the curd is nearing the pitching point, W/h measures the extent to which a standard cylinder of curd loses whey, the liquid being replaced in the solid structure by air. At an earlier stage in the scalding process the capacity of the curd to retain its shape under the force of gravity also affects W/h.

4. Although the cheese-maker judges the consistency of curd suitable for pitching by a complex mixture of properties, it is believed that Wjh will serve as an effective single-value criterion of consistency, suitable for judging pitching time if the acidity is also known.

The reproducibility of Scott Blair's method for measuring curd firmness has been tested and measurements of the “firmness” of cheese curds immediately prior to cutting have been made and related to an expert's opinion. Contrary to her beliefs it was found:

(1) that the mean firmness for normal Cheshire and Double Gloucester curds was the same as that for normal Cheddar curds,

(2) that normal curds, regardless of type, were softer in the summer months than in the winter.

Though confident opinions are often expressed on very small differences in firmness, the smallest difference in modulus which can be correctly appreciated appears to be of the order of 8%.