Short pastry

9.1 Why does our pork pie pastry go soft during storage and what can we do to make our pastry crisper?

The softening of pork pie pastry (and the pastry of many other composite products) arises because of the migration of water from the moist filling to the dry pastry. The driving force for this migration is the difference in the component water activities. Cauvain and Young (2000) give typical water activities for savoury pie components as pastry 0.24, jelly 0.99 and filling 0.98.

Key factors that influence the rate at which water moves between components in savoury pies and the rate at which the pastry softens include the following:

• The storage temperature (Butcher and Hodge, 1984); the lower the temperature, the slower the rate of moisture migration.

• The absolute difference in water activities between the components; the greater the difference, the faster the moisture migration.

Fat also migrates during the manufacture of pies but most of this occurs in the oven when all of the solid fat has turned to oil and is therefore mobile. At ambient or lower temperatures the solid component of the fat cannot move within the pastry matrix. In the past, part of the softening of pie pastry has been attributed to fat migration but if this occurs it is a minor contributor to pastry softening. In fact the migration of oil into the base pastry under the influence of gravity in the oven probably contributes to keeping the base pastry from softening. The oil fills many of the microscopic voids formed in manufacture in the base paste and probably acts as a waterproofing agent so preventing the ingress of significant quantities of water.

As discussed above the main cause of lack of pastry crispness is associated with the movement of water from the moist filling to the drier pastry. The most common way to reduce this problem is to manipulate component water activities to reduce the ERH differential. However, in the case of savoury pastry reformulation of filling and pastry tends to be a limited option so that other means of maintaining pastry crispness must be sought.

One way of achieving a crisper pastry is to increase the initial crispness of the pastry so that even though it softens at the same rate, the crispness at any given storage time will be greater than normal.

In summary the opportunities for improving pastry crispness are:

• lower the temperature to slow the rate of moisture migration;

• reduce the absolute difference in water activities between the components;

• use the hot paste method which gives an initially crisper pastry;

• increase the protein content of the flour used in the manufacture of the paste;

• cool the pies thoroughly before adding the jelly.

References

BUTCHER, G.J. and HODGE, D.G. (1984) Pastry technology: the softening of pork pastry during storage. FMBRA Report No. 116, CCFRA, Chipping Campden, UK.

CAUVAIN, S.P. and YOUNG, L.S. (2000) Bakery Food Manufacture and Quality: Water control and effects, Blackwell Science, Oxford, UK.

9.2 We are producing unbaked meat pies but find that the short pastry lid cracks on freezing. The cracks become larger when the product thaws and during baking the filling may boil out, leaving an unsightly blemish on the surface. Why is this and what can we do about it?

In the freezer the fat in the unbaked pastry contracts by about 10% in volume whereas the aqueous phase expands. This differential in expansion causes stresses to build up in the paste which may exploit any microscopic weaknesses in the paste, turning them into visible cracks. The movement of air across the unbaked product during the freezing operation removes a small amount of moisture from the surface until ice is formed. This drying out of the paste also exacerbates the problem.

The level of gluten formation in short pastry is relatively modest compared with that developed in puff paste or bread doughs. This means that the gluten lacks any significant degree of extensibility and so during sheeting or blocking there is a tendency for the gluten network in the paste to become ruptured, if not visibly then certainly at the microscopic level. The cracks formed are most obvious on the lid because they are readily visible but almost certainly occur in other parts of the product.

In addition to being extensible the gluten network should not be elastic since this increases the stress on the paste. Increased elasticity is most likely to come from overmixing of the paste. The use of a stronger flour may have some advantage in reducing the problem.

Robb (1985) suggested a number of practical remedies for the problem. They included:

• increasing the paste water content;

• reducing the fat content;

• keeping paste mixing times to a minimum consistent with forming an homogeneous paste;

• blast freezing the pies and trying to minimise moisture losses during storage;

• keeping the proportion of trimmings in the lid pastry to a minimum. Incorporating trimmings into the base paste whenever possible.

With some products where the paste fits tightly around the filling, for example sausage rolls and Cornish pasties, there may be some advantage in lowering the filling moisture content to reduce the degree of any physical expansion.

Reference

ROBB, J. (1985) Pastry technology: cracking of frozen meat pie pastry. FMBRA Report No. 126, CCFRA, Chipping Campden, UK.

9.3 Our baked pastries and quiches are baked in individual foils. Why do they have small indents in the base, which project upwards and are pale in colour?

This problem has a similar cause to that described for fermented products in pans (see 6.2), namely that steam is trapped between the pastry and the foil case during baking and since it cannot escape then pressure builds up in some areas and forces the pastry upwards. Since the pastry has not coloured it is likely that this event has occurred early in the baking process.

In the case of the pastry the blocking process itself helps to create the impermeable seal necessary for the steam to remain trapped. It may be that some of the indent is created as the die withdraws, though even hand-blocked products have been known to show the problem.

The most obvious solution to your problem is to use foils with small perforations in the base. However, you should look closely at the location of the holes which should be at the lowest point of the foil, or if the foil concerned has more than one low point then holes should be present in each of the low areas. Even though the holes are small in size, typically, 1 mm, the pressure generated by the hot gases will still allow the steam to diffuse through them.

If the problem persists you should look at your baking conditions. The problem is always exacerbated by baking at high temperatures for short times and with high bottom heat. If you suspect that this is the case then try reducing the temperature and increasing the baking time.

Allowing the pastry case to rest after blocking and before filling and baking can also reduce the problem.

Continue reading here: How can we make the sweet pastry that we use with our apple pies crisper eating

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